Choose and connect a voltmeter, ammeter or ohmmeter correctly, and tell good solder and joints from bad.
Syllabus: Using basic test instruments: voltmeter, ammeter, and ohmmeter; Soldering
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 11 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
| Meter | Measures | Connect |
|---|---|---|
| Voltmeter | voltage (electric potential) | in parallel, across the part |
| Ammeter | current | in series, in the path |
| Ohmmeter | resistance | across the part, power off |
A multimeter is all three in one box, set by its dial: it measures voltage and resistance (and current).
Memory hookVoltage is between two points, so touch both. Current flows through, so be in the way.
An ohmmeter applies a small current and measures the resulting voltage. That's why the circuit must be unpowered when you measure resistance in a circuit.
Putting a meter set to resistance across a live voltage can damage it.
Across a large, discharged capacitor, the meter's current charges it, so the reading keeps increasing.
RememberOhms: power off. Never measure voltage with the dial on resistance.
| Solder | Electronics? |
|---|---|
| Rosin-core, lead-tin | Yes |
| Acid-core | No: the acid flux corrodes electronics (it's for plumbing) |
RememberRough or lumpy = cold joint. Redo it.