First hours with a meter

Reading a meter is not a hand skill in the way flaring is. But safe meter use is a habit with a hazard attached, and habits are built by repetition, not by reading.

You need a multimeter, a low-voltage supply — a battery is ideal — some resistors, wire, a switch and a lamp. None of it is aviation-specific and all of it is cheap.

Do not practice on an aircraft.

Session 1 — Predict, then measure

This session is the whole unit in twenty minutes.

1. Build a series circuit: battery, switch, lamp.
2. Before connecting the meter, write down what you expect the supply voltage to be and what you expect across the lamp.
3. Measure. Compare.
4. Now put a resistor in series with the lamp. Predict the two voltages before measuring.
5. Measure.

What you are learning: the prediction is the skill. A meter reading on its own is a number; a reading you expected — or did not — is information (GEN-A Concepts §2).

Expect your first predictions to be wrong. That is the useful part: a prediction that fails tells you which part of your model is wrong, and there is nowhere else to get that.

Session 2 — Series and parallel, until the arithmetic is intuition

1. Three resistors in series. Predict total resistance, current, and each voltage drop. Measure all of them.
2. Check that your drops sum to the supply. They will, and confirming it builds the habit that finds faults in Session 4.
3. Two resistors in parallel. Predict total resistance. Measure.
4. Confirm the parallel total is smaller than the smaller resistor. If your prediction was larger, the arithmetic is inverted.

What will be wrong on your first attempts:

Session 3 — The two ways to destroy a meter

Do these deliberately, on a battery and a resistor, where nothing matters.

1. Set the meter to current and connect it across the battery. (Use a low-voltage cell and expect to blow the meter's fuse — that is the lesson, and the fuse is the cheapest part of it.)
2. Set the meter to resistance and connect it to a live circuit. Note the meaningless reading.
3. Replace the fuse. Note how long it took and what it cost.

What you are learning: both mistakes come from the same root — the meter was set for one thing and connected as if for another. The habit that prevents both is setting the function and returning the leads to the voltage sockets before you move to the next measurement.

This is the session people skip and then repeat on an aircraft with a meter that is not theirs.

Session 4 — Build a fault, then find it

The session that turns measurement into troubleshooting.

1. Build a circuit with four connections in series with a lamp — screw terminals, chocolate block, anything.
2. Deliberately make one connection bad: leave a strand of insulation under the screw, or barely nip it up.
3. Turn it on. The lamp will probably still light, perhaps dimly.
4. Test continuity with the circuit off. It will pass. Note that.
5. Now do a voltage drop test with the circuit on and loaded, across each connection in turn.

What you will see: three connections reading near zero, and one reading volts. You have just found a fault that continuity said was not there — which is the point of GEN-A Concepts §3 and the single most useful thing in this unit.

6. Repeat with the bad connection somewhere else, without looking, and find it again.

Session 5 — Resistance in isolation

1. Measure a resistor out of circuit. Note the value against its color code.
2. Solder or connect it in parallel with another and measure again without disconnecting.
3. Note that the reading is neither resistor.

What you are learning: in-circuit resistance measurements read the whole network. Disconnect one end, always.

Session 6 — Static discipline, which has no feedback

You cannot practice this and see a result, which is exactly the problem (GEN-A Concepts §1).

1. Read the handling requirements for electrostatic-sensitive devices.
2. Practice the sequence with an ordinary component: ground yourself first, keep the device in its protective packaging until the moment of installation, avoid touching pins, work on a grounded surface.
3. Do it every time you handle anything electronic, whether or not it is marked sensitive.

What you are learning: the habit has to be unconditional, because you will never receive feedback telling you it mattered. A unit you damaged will fail weeks later, somewhere else, and nobody will connect it to you.

What you should be able to do at the end

• Predict a reading before taking it, and be roughly right.
• Find a high-resistance connection by voltage drop, under load, in a circuit you did not build.
• Set up a meter without thinking about it, and return the leads to the voltage sockets by reflex.
• Say what is on the other end of the probes before they touch anything.

License

CC BY-SA 4.0 (Licensing).