Ode to a Volt Meter: Of Linear Equations and OSHA Compliance

Part I: The Ohm

The most natural unit is the ohm:

Resistance found in rock, metal, wood, and foam.

It’s the strength which clings to valence electrons,

Allowing current to pass through or reflect on.

 

Conductors are things that have low resistance.

That’s a real handy feature for wires with long distance.

Low resistance allows a more free flow of current.

When we need higher power, more Ohms would deter it.

Conduction is crucial for circuit board traces,

Multiple layers for those hard-to-reach places.

Push buttons and switches also conduct,

At least when you press them; ‘til then they obstruct.

 

When resistance is high, we call this an insulator.

In between is a semiconductor but we’ll get to that later.

In most common circuits, Volts and Ohms are alike,

If the resistance goes up, you can bet voltage will spike.

Insulators are plastic and wrapped around wires.

If that protective layer fails, it’s going to cause fires.

Measuring Ohms is extremely important.

It’s the only one you can read without live circuit current.

 

Semiconductors can be pretty tricky:

The electronics might move … or might not; they’re really quite picky.

With the right mix of charge, both plusses and minuses,

The process of doping allows silicon biases.

With just the right application of volts to the gate,

A semiconductor flows current at a very precise rate.

Solid-state relays and inverter drives:

These both leverage MOSFETS to keep control system alive.

 

Part II: The Volt

The Volt is a circuit’s most important unit:

It provides the force driving electrons all through it.

But don’t be fooled by the state of a button or switch;

Even if it’s open, the voltage could still make you twitch.

Voltage is only the potential for action;

It can come from chemicals, motion, or friction.

 

Water and wind are ways by which a volt generates:

The waveform oscillates or we might say alternates.

That back-and-forth motion that this electricity produces

Gives us the title AC; it has a lot of great uses.

AC voltage drives huge industrial motors,

Using inductive magnetic fields spinning the rotors.

The most common waves come in one or three phases:

Single-phase for your houses but it’s three for big places.

 

If a battery is your main power source,

Then it means you are running on DC of course.

Direct current sources have minus and plus sides,

And a nice constant voltage is this method’s upside.

24 volt supplies always provide DC,

And troubleshooting failures is often quite easy.

Use a meter to measure across every device,

To find the spot where it’s open or perhaps short caused by a slice.

 

When testing for voltage, check a live circuit first,

Just in case your voltmeter was dead, or a fuse somehow burst.

Then move on to the actual live test point with leads.

You should read a voltage between zero and the amount the load needs.

And finally, when you are finished reading that value,

Test a known circuit, so you know the meter didn’t fail you.

This process is known as "live-dead-live" reading,

And it’s a great trick to know so you keep on breathing.

 

Part III: The Amp

Contrary to what you might have been told,

Current is not the unit all the devices controlled.

You never push amperage through a switch in your home.

Current’s just the result of Volts divided by Ohms.

 

It’s still really important, because without electrical flow,

There’d be no more power; motors wouldn’t spin, fans wouldn’t blow.

But if we want to determine the power,

We must read volts and the ohms, taken right at that hour.

If the load is the point where we sense a temp rise,

That means resistance is low and breaker’s wrong size.

But if the heat is rising at a wire or junction,

The resistance is too high; that should not be their function.

 

In pretty much all circuits, home or industrial,

The load should be the only resistance not negligible.

Unless it’s our goal to control current flow.

In those cases, control boards may see Ohms high or low.

But at the end of the day, Volts times Amps equal heat,

So if Ohms are small but non-zero, stuff glows; it’s not neat.

To locate a problem where current’s too much or too little,

Again think of Ohms to help track down the riddle.

 

I hope that you’ve learned something of circuits and wiring.

I’ll admit that the topic can get pretty tiring.

But next time you’re faced with some problem electronics,

Just remember these tips and I’m sure you jump on it.

 

Featured image used courtesy of Canva