Fault Analysis of Simple Circuits

Suppose a voltmeter registers 0 volts between test points C and F, but measures 24 volts between those same test points when the connection between B and C is broken:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline Q_1~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline Q_1~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose this electric-driven air compressor cycles between 60 PSI and 105 PSI when the switch is in the “Auto” position, and cycles between 102 PSI and 105 PSI when in the “Hand” position:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline PSHH~Failed~open & & \\ \hline PSH~Failed~open & & \\ \hline PSL~Failed~open & & \\ \hline Aux~“M”~contact~failed~open & & \\ \hline PSHH~Failed~shorted & & \\ \hline PSH~Failed~shorted & & \\ \hline PSL~Failed~shorted & & \\ \hline Aux~“M”~contact~failed~shorted & & \\ \hline \end{array}$$

Suppose this electric-driven air compressor refuses to start when the switch is in the “Auto” position, but starts up immediately when the switch is placed in the “Hand” position. The first test performed by a technician is to measure AC voltage between test points A and F with the switch in the “Auto” position. There, the meter registers 117 volts AC. You are then called in to help:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline PSHH~Failed~open & & \\ \hline PSH~Failed~open & & \\ \hline PSL~Failed~open & & \\ \hline “Hand”~switch~position~failed~open & & \\ \hline “Auto”~switch~position~failed~open & & \\ \hline OL~contact~failed~open & & \\ \hline Aux~“M”~contact~failed & & \\ \hline Contactor~“M”~coil~failed~open & & \\ \hline \end{array}$$

An Automation Direct model C0-08TD2 “sourcing” DC output PLC module uses the following internal circuitry to switch DC power to a load:

Suppose the microprocessor is sending a “high” (1) signal to the switching circuitry, but the DC load refuses to energize. Using your DC voltmeter, you measure 24.7 volts DC between the “+V” and “Com” terminals, and 0 volts DC between the “Out” and “Com” terminals.

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Diode~D_1~Failed~shorted & & \\ \hline Diode~D_2~Failed~open & & \\ \hline Diode~D_3~Failed~open & & \\ \hline Diode~D_4~Failed~open & & \\ \hline Transistor~Q_1~Failed~open & & \\ \hline Transistor~Q_2~Failed~open & & \\ \hline Transistor~Q_3~Failed~shorted & & \\ \hline Capacitor~C_1~Failed~open & & \\ \hline Resistor~R_1~Failed~shorted & & \\ \hline Resistor~R_2~Failed~shorted & & \\ \hline Resistor~R_3~Failed~open & & \\ \hline Resistor~R_4~Failed~open & & \\ \hline Resistor~R_5~Failed~shorted & & \\ \hline Resistor~R_6~Failed~open & & \\ \hline \end{array}$$

An Automation Direct model C0-08TD1 “sinking” DC output PLC module uses the following internal circuitry to switch DC power to a load:

Suppose the microprocessor is sending a “high” (1) signal to the switching circuitry, but the DC load refuses to energize. Using your DC voltmeter, you measure 24.7 volts DC between the “+V” and “Com” terminals, and 23.2 volts DC between the “Out” and “Com” terminals.

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Diode~D_1~Failed~open & & \\ \hline Diode~D_2~Failed~open & & \\ \hline Diode~D_3~Failed~open & & \\ \hline Diode~D_4~Failed~open & & \\ \hline Transisto~Q_1~Failed~open & & \\ \hline Transistor~Q_2~Failed~open & & \\ \hline Transistor~Q_3~Failed~open & & \\ \hline Resistor~R_1~Failed~open & & \\ \hline Resistor~R_2~Failed~open & & \\ \hline Resistor~R_3~Failed~open & & \\ \hline Resistor~R_4~Failed~open & & \\ \hline Resistor~R_5~Failed~open & & \\ \hline Resistor~R_6~Failed~open & & \\ \hline \end{array}$$

Suppose the voltmeter in this circuit registers a strong negative voltage (note the test lead polarity +/- and consider that the voltage is negative, this means ‘-’ is at a higher voltage than ‘+’).

A test using a digital multimeter (DMM) shows the voltage between test points A and B to be 0.8 volts:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \surd \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_5~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline R_5~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose the voltmeter in this bridge circuit registers a strong negative voltage (note the test lead polarity +/- and consider that the voltage is negative, this means ‘-’ is at a higher voltage than ‘+’).

A test using a digital multimeter (DMM) shows the voltage between test points A and C to be 4 volts:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_5~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline R_5~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose the voltmeter in this bridge circuit registers a strong {\it positive} voltage. A test using a digital multimeter (DMM) shows the voltage between test points {\bf A} and {\bf B} to be 12 volts:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose the voltmeter in this bridge circuit registers a strong {\it negative} voltage:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 22 volts between test points {\bf A} and {\bf D}:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline Q_1~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline Q_1~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

This pictorial diagram shows the wiring connections for a simple pressure control loop, where a loop-powered 4-20 mA pressure transmitter sends a signal to a Honeywell controller, which in turn sends another 4-20 mA signal to a control valve:

If an operator informs you that the pressure indicated by the Honeywell controller is below range (“pegged” full downscale, reading -10

Suppose a voltmeter registers 6 volts between test points {\bf C} and {\bf D} while the pushbutton is released (not pressed), and also 6 volts between the same test points while the pushbutton is pressed:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Switch~Failed~open & & \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline Switch~Failed~shorted & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 24 volts between test points {\bf E} and {\bf C} while the pushbutton is released (not pressed), and 0 volts between test points {\bf A} and {\bf B} while the pushbutton is pressed:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Switch~Failed~open & & \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline Switch~Failed~shorted & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf E} and {\bf F}, and 9 volts between test points {\bf F} and {\bf H} when the connection between {\bf F} and {\bf H} has been broken:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf B} and {\bf C}, and measures 24 volts between those same two test points after the connection has been broken between points {\bf A} and {\bf B}:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 9 volts between test points {\bf B} and {\bf C}, but measures 18 volts between those same two test points after the connection has been broken between points {\bf E} and {\bf G}:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf A} and {\bf C}, and also measures 0 volts between those same two test points after the connection has been broken between points {\bf A} and {\bf B}:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf C} and the nearest lead of resistor R_2 registers 0 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf F} and the nearest lead of resistor R_4 registers 0 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf A} and {\bf D} in this series-parallel circuit:

Determine the diagnostic value of each of the following tests. Assume only one fault in the system, including any single component or any single wire/cable/tube connecting components together. If a proposed test could provide new information to help you identify the location and/or nature of the one fault, mark “yes.” Otherwise, if a proposed test would not reveal anything relevant to identifying the fault (already discernible from the measurements and symptoms given so far), mark “no.’‘

$$\begin{array} {|l|l|} \hline Diagnostic~test & Yes & No \\ \hline Measure~V_{CD}~with~power~applied & & \\ \hline Measure~V_{DF}~with~power~applied & & \\ \hline Measure~V_{DE}~with~power~applied & & \\ \hline Measure~I_{R1}~with~power~applied & & \\ \hline Measure~I_{R2}~with~power~applied & & \\ \hline Measure~R_{AB}~with~source~disconnected~from~C & & \\ \hline Measure~R_{DF}~with~source~disconnected~from~E & & \\ \hline Measure~R_{CF}~with~source~disconnected~from~C & & \\ \hline Measure~R_{CD}~with~wire~disconnected~between~{\bf A} and C & & \\ \hline Measure~R_{CD}$ with R_3 disconnected from D & & \\ \hline \end{array}$$

Suppose an operator discovers that the natural gas make-up valve in this fuel gas pressure control system is shut when the controller output is 78

{\bullet} Test 1: Measured 18.6 volts DC between PT-528 transmitter terminals.

{\bullet} Test 2: Measured supply air pressure at PV-528a to be 22 PSIG.

{\bullet} Test 3: Measured 0 volts DC between terminals 25 and 26.

{\bullet} Test 4: Measured 27 volts DC between terminals 5 and 6.

{\bullet} Test 5: Measured 27 volts DC between terminals 19 and 20.

{\bullet} Test 6: Measured 27 volts DC between terminals 15 and 16.

Identify any useful information about the nature or location of the fault derived from the results of each test, in order of the tests performed. If the test is not useful (i.e. provides no new information), mark it as such. Assuming there is only one fault in the circuit, identify the location and nature of the fault as precisely as you can from the test results shown above.

This reversing motor control circuit has a problem: it runs just fine in reverse, but not at all in the forward direction. A technician begins diagnosing the circuit, following the steps shown (in order):

{\bullet} Test 1: Jumpered points {\bf F} and {\bf G} while pressing the “Forward” pushbutton. Motor did not turn.

{\bullet} Test 2: Measured 117 VAC between points {\bf G} and {\bf H} while pressing “Forward” pushbutton.

{\bullet} Test 3: Measured 478 VAC between points {\bf M} and {\bf N} while pressing “Forward” pushbutton.

{\bullet} Test 4: Measured 239 VAC between points {\bf M} and {\bf P} while pressing “Forward” pushbutton.

{\bullet} Test 5: Measured 239 VAC between points {\bf N} and {\bf P} while pressing “Forward” pushbutton.

Identify any useful information about the nature or location of the fault derived from the results of each test, in order of the tests performed. If the test is not useful (i.e. provides no new information), mark it as such. Assuming there is only one fault in the circuit, identify the location and nature of the fault as precisely as you can from the test results shown above.

This conveyor belt control circuit has a problem. The siren energizes when the “Start” pushbutton is pressed, but the conveyor belt never moves. The siren remains energized until the “Stop” button is pressed. A technician begins diagnosing the circuit, following the steps shown (in order). His first action is to press the “Start” switch so that the siren is continuously activated, before he begins any diagnostic tests:

{\bullet} Test 1: Measured 120 VAC between points {\bf A} and {\bf E}.

{\bullet} Test 2: Measured 120 VAC between points {\bf N} and {\bf L}.

{\bullet} Test 3: Measured 0 VAC between points {\bf J} and {\bf K}.

{\bullet} Test 4: Measured 0 VAC between points {\bf D} and {\bf M}.

{\bullet} Test 5: Measured 120 VAC between points {\bf A} and {\bf D}.

Identify any useful information about the nature or location of the fault derived from the results of each test, in order of the tests performed. If the test is not useful (i.e. provides no new information), mark it as such. Assuming there is only one fault in the circuit, identify the location and nature of the fault as precisely as you can from the test results shown above.

This air compressor control circuit has a problem. The air compressor refuses to start even when the air pressure is zero PSI. A technician begins diagnosing the circuit, following the steps shown (in order):

{\bullet} {\bf Test 1:} Measured 120 VAC between points {\bf A} and {\bf C}, with “Hand/Off/Auto” switch in the “Auto” position.

{\bullet} {\bf Test 2:} Measured 120 VAC between points {\bf A} and {\bf D}, with “Hand/Off/Auto” switch in “Auto” position.

{\bullet} {\bf Test 3:} Measured 0 VAC between points {\bf E} and {\bf C}, with “Hand/Off/Auto” switch in “Auto” position.

{\bullet} {\bf Test 4:} Jumpered points {\bf A} and {\bf B}, with “Hand/Off/Auto” switch in “Auto” position. The motor did not start.

Identify any useful information about the nature or location of the fault derived from the results of each test, in order of the tests performed. If the test is not useful (i.e. provides no new information), mark it as such. Assuming there is only one fault in the circuit, identify the location and nature of the fault as precisely as you can from the test results shown above.

Suppose the electric motor refuses to run when the “Run” pushbutton switch is pressed, whether the speed switch is set to “Fast” or to “Slow.” A technician begins diagnosing the circuit, following the steps shown (in order):

{\bullet} {\bf Test 1:} Measured 12 volts DC between points {\bf A} and {\bf B}, with “Run” switch pressed and speed switch in “Fast” position.

{\bullet} {\bf Test 2:} Measured 0 volts DC between points {\bf A} and {\bf C}, with “Run” switch unpressed and speed switch in “Fast” position.

{\bullet} {\bf Test 3:} Measured 12 volts DC between points {\bf G} and {\bf D}, with “Run” switch pressed and speed switch in “Fast” position.

{\bullet} {\bf Test 4:} Measured 25 ohms between points {\bf G} and {\bf E}, with “Run” switch unpressed and speed switch in “Fast” position.

{\bullet} {\bf Test 5:} Measured 12 volts DC between points {\bf A} and {\bf F}, with “Run” switch pressed and speed switch in “Fast” position.

Identify any useful information about the nature or location of the fault derived from the results of each test, in order of the tests performed. If the test is not useful (i.e. provides no new information), mark it as such. Assuming there is only one fault in the circuit, identify the location and nature of the fault as precisely as you can from the test results shown above.

Suppose the electric motor refuses to run when the “Run” pushbutton switch is pressed. A technician begins diagnosing the circuit, following the steps shown (in order):

{\bullet} {\bf Test 1:} Measured 0 volts DC between points {\bf C} and {\bf D}, with “Run” switch pressed.

{\bullet} {\bf Test 2:} Measured 0 volts DC between points {\bf A} and {\bf C}, with “Run” switch unpressed.

{\bullet} {\bf Test 3:} Measured 12 volts DC between points {\bf A} and {\bf B}, with “Run” switch pressed.

{\bullet} {\bf Test 4:} Measured 12 volts DC between points {\bf C} and {\bf B}, with “Run” switch unpressed.

{\bullet} {\bf Test 5:} Measured 3.5 ohms between points {\bf E} and {\bf F}, with “Run” switch unpressed.

Identify any useful information about the nature or location of the fault derived from the results of each test, in order of the tests performed. If the test is not useful (i.e. provides no new information), mark it as such. Assuming there is only one fault in the circuit, identify the location and nature of the fault as precisely as you can from the test results shown above.

Suppose the electric motor refuses to run when the “Run” pushbutton switch is pressed. A technician begins diagnosing the circuit, following the steps shown (in order):

{\bullet} {\bf Test 1:} Measured 2.8 ohms between points {\bf E} and {\bf F}, with “Run” switch unpressed.

{\bullet} {\bf Test 2:} Measured 12 volts between points {\bf A} and {\bf F}, with “Run” switch unpressed.

{\bullet} {\bf Test 3:} Measured 12 volts between points {\bf A} and {\bf B}, with “Run” switch unpressed.

{\bullet} {\bf Test 4:} Measured 12 volts between points {\bf A} and {\bf C}, with “Run” switch pressed.

Identify any useful information about the nature or location of the fault derived from the results of each test, in order of the tests performed. If the test is not useful (i.e. provides no new information), mark it as such. Assuming there is only one fault in the circuit, identify the location and nature of the fault as precisely as you can from the test results shown above.

This pictorial diagram shows the wiring connections for a simple pressure control loop, where a loop-powered 4-20 mA pressure transmitter sends a signal to a Honeywell controller, which in turn sends another 4-20 mA signal to a control valve:

Suppose the operator informs you that the control valve refuses to open, no matter what value she sets the output of the controller in manual mode. Your job now is to diagnose the problem in this control loop using only basic test equipment (e.g. digital multimeter, hand tools).

Determine the diagnostic value of each of the following tests. Assume only one fault in the system, including any single component or any single wire/cable/tube connecting components together. If a proposed test could provide new information to help you identify the location and/or nature of the one fault, mark “yes.” Otherwise, if a proposed test would not reveal anything relevant to identifying the fault (already discernible from the measurements and symptoms given so far), mark “no.’‘

$$\begin{array} {|l|l|} \hline Diagnostic~test & Yes & No \\ \hline Place~controller~in~auto~mode & & \\ \hline Measure~V_{AB}~with~output~set~to~100 & & \\ \hline Measure~V_{5-4}~with~output~set~to~100 & & \\ \hline Measure~V_{8-7}~with~output~set~to~50 & & \\ \hline Crack~open~fitting~at~‘S’~port~on~I/P~transducer & & \\ \hline Crack~open~fitting~at~‘O’~port~on~I/P~transducer & & \\ \hline Press~I/P~transducer’s~flapper~closer~to~nozzle & & \\ \hline Pull~I/P~transducer’s~flapper~away~from~nozzle & & \\ \hline Tighten~nuts~compressing~the~valve~stem~packing & & \\ \hline Loosen~nuts~compressing~the~valve~stem~packing & & \\ \hline Measure~output~voltage~of~DC~power~supply & & \\ \hline Measure~voltage~across~pressure~transmitter~terminals & & \\ \hline Measure~voltage~across~I/P~transducer~terminals & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf E} and {\bf F} in this circuit:

Determine the diagnostic value of each of the following tests. Assume only one fault in the system, including any single component or any single wire/cable/tube connecting components together. If a proposed test could provide new information to help you identify the location and/or nature of the one fault, mark “yes.” Otherwise, if a proposed test would not reveal anything relevant to identifying the fault (already discernible from the measurements and symptoms given so far), mark “no.’‘

$$\begin{array} {|l|l|} \hline Diagnostic~test & Yes & No \\ \hline Measure~V_{AC}~with~power~applied & & \\ \hline Measure~V_{JK}~with~power~applied & & \\ \hline Measure~V_{CK}~with~power~applied & & \\ \hline Measure~I_{R1}~with~power~applied & & \\ \hline Measure~I_{R2}~with~power~applied & & \\ \hline Measure~I_{R3}~with~power~applied & & \\ \hline Measure~R_{AC}~with~source~disconnected~from~R_1 & & \\ \hline Measure~R_{DF}~with~source~disconnected~from~R_1 & & \\ \hline Measure~R_{EG}~with~source~disconnected~from~R_1 & & \\ \hline Measure~R_{HK}~with~source~disconnected~from~R_1 & & \\ \hline \end{array}$$

Suppose a voltmeter registers 24 volts between test points {\bf A} and {\bf B} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 16 volts between test points {\bf C} and {\bf E} in this series-parallel circuit:

Determine the diagnostic value of each of the following tests. Assume only one fault in the system, including any single component or any single wire/cable/tube connecting components together. If a proposed test could provide new information to help you identify the location and/or nature of the one fault, mark “yes.” Otherwise, if a proposed test would not reveal anything relevant to identifying the fault (already discernible from the measurements and symptoms given so far), mark “no.’‘

$$\begin{array} {|l|l|} \hline Diagnostic~test & Yes & No \\ \hline Measure~V_{CD}~with~power~applied & & \\ \hline Measure~V_{DF}~with~power~applied & & \\ \hline Measure~I_{R1}~with~power~applied & & \\ \hline Measure~I_{R2}~with~power~applied & & \\ \hline Measure~R_{AB}~with~power~applied & & \\ \hline Measure~R_{DF}~with~power~applied & & \\ \hline Measure~R_{CF}~with~power~applied & & \\ \hline Measure~R_{AB}~with~source~disconnected~from~A & & \\ \hline Measure~R_{DF}~with~source~disconnected~from~A & & \\ \hline Measure~R_{CF}~with~source~disconnected~from~B & & \\ \hline Measure~R_{CF}~with~wire~disconnected~between~A and {\bf C} & & \\ \hline \end{array}$$

Suppose the lamp refuses to light up when the pushbutton switch is pressed. A voltmeter registers 0 volts between test points {\bf A} and {\bf D} in the circuit while the pushbutton is pressed:

Determine the diagnostic value of each of the following tests. Assume only one fault in the system, including any single component or any single wire/cable/tube connecting components together. If a proposed test could provide new information to help you identify the location and/or nature of the one fault, mark “yes.” Otherwise, if a proposed test would not reveal anything relevant to identifying the fault (already discernible from the measurements and symptoms given so far), mark “no.’‘

$$\begin{array} {|l|l|} \hline Diagnostic~test & Yes & No \\ \hline Measure~V_{EF}~with~switch~pressed & & \\ \hline Measure~V_{CD}~with~switch~pressed & & \\ \hline Measure~V_{CB}~with~switch~pressed & & \\ \hline Measure~V_{CE}~with~switch~pressed & & \\ \hline Measure~R_{AB}~with~switch~pressed & & \\ \hline Measure~V_{EF}~with~switch~unpressed & & \\ \hline Measure~V_{CD}~with~switch~unpressed & & \\ \hline Measure~V_{CB}~with~switch~unpressed & & \\ \hline Measure~V_{CE}~with~switch~unpressed & & \\ \hline Measure~R_{AB}~with~switch~unpressed & & \\ \hline \end{array}$$

Suppose the lamp refuses to light up. A voltmeter registers 24 volts between test points {\bf C} and {\bf D}:

First, list all the possible (single) faults that could account for all measurements and symptoms in this circuit, including failed wires as well as failed components:

Now, determine the diagnostic value of each of the following tests, based on the faults you listed above. If a proposed test could provide new information to help you identify the location and/or nature of the one fault, mark “yes.” Otherwise, if a proposed test would not reveal anything relevant to identifying the fault (already discernible from the measurements and symptoms given so far), mark “no.’‘

$$\begin{array} {|l|l|} \hline Diagnostic~test & Yes & No \\ \hline Measure~V_{CF}$ & & \\ \hline Measure~V_{ED}$ & & \\ \hline Measure~V_{AB}$ & & \\ \hline Measure~V_{AD}$ & & \\ \hline Measure~V_{CB}$ & & \\ \hline Measure~V_{EF}$ & & \\ \hline Measure current through wire connecting A and C & & \\ \hline Jumper A and C together & & \\ \hline Jumper B and D together & & \\ \hline Jumper A and B together & & \\ \hline \end{array}$$

This pressure-measurement system seems to have a problem. The pressure gauge (PG) indicates 30 PSI, but the pressure indicator (PI) reads less than 0 PSI (“pegged” fully down-scale). A voltmeter connected between terminals 7 and 8 registers 24 VDC:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline 250 ohm resistor~Failed~open & & \\ \hline 100~mA~fuse~blown & & \\ \hline 1.5~A~fuse~blown & & \\ \hline Cable 1~Failed~open & & \\ \hline Cable 3~Failed~open & & \\ \hline Cable 1~Failed~shorted & & \\ \hline Cable 4~Failed~shorted & & \\ \hline \end{array}$$

This pressure-measurement system seems to have a problem. The pressure gauge (PG) indicates 30 PSI, but the pressure indicator (PI) reads over 50 PSI (“pegged” fully up-scale). A voltmeter connected between terminals 4 and 2 registers 24 VDC:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline 250 ohm resistor~Failed~open & & \\ \hline 100 mA~fuse~blown & & \\ \hline 1.5~A~fuse~blown & & \\ \hline Cable 1~Failed~open & & \\ \hline Cable 4~Failed~open & & \\ \hline Cable 1~Failed~shorted & & \\ \hline Cable 4~Failed~shorted & & \\ \hline \end{array}$$

This pressure-measurement system seems to have a problem. The pressure gauge (PG) indicates 30 PSI, but the pressure indicator (PI) reads less than 0 PSI (“pegged” fully down-scale). A voltmeter connected between terminals 7 and 8 registers 0 VDC:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline 250 ohm resistor~Failed~open & & \\ \hline 100 mA~fuse~blown & & \\ \hline 1.5~A~fuse~blown & & \\ \hline Cable 1~Failed~open & & \\ \hline Cable 4~Failed~open & & \\ \hline Cable 1~Failed~shorted & & \\ \hline Cable 4~Failed~shorted & & \\ \hline \end{array}$$

This pictorial diagram shows the wiring connections for a simple pressure control loop, where a loop-powered 4-20 mA pressure transmitter sends a signal to a Honeywell controller, which in turn sends another 4-20 mA signal to a control valve:

If an operator informs you that the control valve refuses to open even in manual mode, what types and locations of electrical faults might you suspect? Are there any non-electrical faults which might also cause this to happen?

This pictorial diagram shows the wiring connections for a simple pressure control loop, where a loop-powered 4-20 mA pressure transmitter sends a signal to a Honeywell controller, which in turn sends another 4-20 mA signal to a control valve:

If an operator informs you that the pressure indicated by the Honeywell controller is above range (“pegged” full upscale, reading +110

Suppose a voltmeter registers 0 volts between test points {\bf C} and {\bf F} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test points {\bf E} and {\bf F} registers 4 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test points {\bf B} and {\bf D} registers 0 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf C} and {\bf D} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test points {\bf E} and {\bf C} registers 6 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 8 volts between test points {\bf A} and {\bf F} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf D} and the nearest lead of resistor R_2 registers 0 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf C} and the nearest lead of resistor R_3 registers 4 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf C} and the nearest lead of resistor R_1 registers 0 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 6 volts between test points {\bf E} and {\bf C} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test points {\bf D} and {\bf B} registers 16 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 12 volts between test points {\bf C} and {\bf D} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 6 volts between test points {\bf C} and {\bf B} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 18 volts between test points {\bf E} and {\bf C} while the pushbutton is released (not pressed), and 0 volts between test points {\bf A} and {\bf B} while the pushbutton is pressed:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Switch~Failed~open & & \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline Switch~Failed~shorted & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf E} and {\bf C} while the pushbutton is released (not pressed), and 0 volts between test points {\bf B} and {\bf D} while the pushbutton is pressed:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Switch~Failed~open & & \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline Switch~Failed~shorted & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose the lamp refuses to light up when the pushbutton switch is pressed. A voltmeter registers 12 volts between test points {\bf C} and {\bf E} in the circuit while the pushbutton is released (not pressed):

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Open~wire~between~A~and~C & & \\ \hline Open~wire~between~B~and~D & & \\ \hline Open~wire~between~D~and~F & & \\ \hline Lamp~Failed~open & & \\ \hline Switch~Failed~open & & \\ \hline Lamp~Failed~shorted & & \\ \hline Switch~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose the lamp refuses to light up when the pushbutton switch is pressed. A voltmeter registers 0 volts between test points {\bf E} and {\bf D} in the circuit while the pushbutton is pressed:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Open~wire~between~A~and~C & & \\ \hline Open~wire~between~B~and~D & & \\ \hline Open~wire~between~D~and~F & & \\ \hline Lamp~Failed~open & & \\ \hline Switch~Failed~open & & \\ \hline Lamp~Failed~shorted & & \\ \hline Switch~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose the lamp refuses to light up when the pushbutton switch is pressed. A voltmeter registers 0 volts between test points {\bf A} and {\bf D} in the circuit while the pushbutton is pressed:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline Open~wire~between~A~and~C & & \\ \hline Open~wire~between~B~and~D & & \\ \hline Open~wire~between~D~and~F & & \\ \hline Lamp~Failed~open & & \\ \hline Switch~Failed~open & & \\ \hline Lamp~Failed~shorted & & \\ \hline Switch~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Identify which of these are true statements:

{1.} Between two points that are electrically common to each other, there is guaranteed to be zero (or nearly zero) voltage.

{2.} If zero voltage is measured between two points, those points must be electrically common to each other.

{3.} Between two points that are not electrically common to each other, there is guaranteed to be voltage.

{4.} If voltage is measured between two points, those points cannot be electrically common to each other.

Suppose a voltmeter registers 4 volts between test points {\bf E} and {\bf C} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 12 volts between test points {\bf D} and {\bf A} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 13.33 volts between test points {\bf D} and {\bf E} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 12 volts between test points {\bf A} and {\bf D} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 6 volts between test points {\bf D} and {\bf E} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf F} and {\bf E} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 20 volts between test points {\bf D} and {\bf E} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf A} and {\bf D} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_4~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline R_4~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf F} and the nearest lead of resistor R_3 registers 0 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Everything I know about troubleshooting, I learned from Tyler Durden (with respects to the movie {\it Fight Club}):

{The Rules of \underline{ Fault Club}}

(1) Don’t try to find the fault by looking for it—perform diagnostic tests instead

(2) {\it Don't try to find the fault by looking for it -- perform diagnostic tests instead!}

(3) The troubleshooting is over when you have correctly identified the nature and location of the fault

(4) It’s just you and the fault—don’t ask for help until you have exhausted your resources

(5) Assume one fault at a time in a proven system, unless the data proves otherwise

(6) No new components allowed—replacing suspected bad components with new is a waste of time and money

(7) We will practice as many times as we have to until you master this

(8) Troubleshooting is not a spectator sport:

For each of these rules, explain their rationale.

Suppose a voltmeter registers 0 volts between test points {\bf C} and {\bf E} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 4 volts between test points {\bf A} and {\bf C} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 24 volts between test points {\bf C} and {\bf A} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Current~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 0 volts between test points {\bf D} and {\bf B} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 18 volts between test points {\bf C} and {\bf E} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf D} and the nearest lead of voltage source registers 9 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose an ammeter inserted between test point {\bf C} and the nearest lead of resistor R_2 registers 9 mA in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$

Suppose a voltmeter registers 16 volts between test points {\bf F} and {\bf D} in this series-parallel circuit:

Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no coincidental faults), determining whether or not each fault could independently account for all measurements and symptoms in this circuit.

$$\begin{array} {|l|l|} \hline Fault & Possible & Impossible \\ \hline R_1~Failed~open & & \\ \hline R_2~Failed~open & & \\ \hline R_3~Failed~open & & \\ \hline R_1~Failed~shorted & & \\ \hline R_2~Failed~shorted & & \\ \hline R_3~Failed~shorted & & \\ \hline Voltage~source~dead & & \\ \hline \end{array}$$