Test Equipment
A technician is only as good as their ability to measure. The Associate CET exam expects you to know what each instrument measures, how to connect it correctly, and its limits. This guide covers the core bench instruments — the multimeter, oscilloscope, signal sources, spectrum analyzer, and logic probe.
The DMM is the everyday workhorse. It measures DC and AC voltage, DC and AC current, resistance, and continuity, and most add diode test, capacitance, and frequency. The display is typically an LCD.iThe exam notes a DMM's display is usually an LCD — low power, good for battery-operated meters, though it can be hard to read in cold temperatures. A digital meter is generally preferred over an analog VOM for convenience and accuracy — no needle to interpret, no parallax error.
| Connect it… | Rule |
|---|---|
| Voltage | In parallel with the component — across it. A voltmeter has very high input impedance so it draws almost no current. |
| Current | In series — the circuit must be broken and the meter inserted so all current flows through it. A low-resistance shunt. |
| Resistance | On a de-energized circuit only — the meter supplies its own test current. Measuring a live circuit gives wrong readings and can damage the meter. |
| Continuity | De-energized; the meter beeps when resistance is near zero (a complete path). |
The oscilloscope draws a graph of voltage versus time — it's how you actually see a waveform's shape, amplitude, frequency, and timing. The two axes are the whole story:
Read amplitude by counting vertical divisions × the volts/div setting, and period by counting horizontal divisions × the time/div setting — then frequency is f = 1/T. A dual-trace scope shows two signals at once (two vertical inputs); it displays them by alternating sweepsiAlt / chop: a dual-trace analog scope shows two channels by alternating complete sweeps (alt mode, for fast signals) or rapidly switching mid-sweep (chop, for slow ones). between channels. A Digital Storage Oscilloscope (DSO) samples the signal and uses a microprocessor and memory to capture and hold it for analysis — letting you freeze, zoom, and measure single events.
Function / signal generator
Produces test waveforms — sine, square, triangle — at a set frequency and amplitude. Used to inject a known signal for tracing through a circuit. For audio work, ~1 kHz is the standard test tone.
RF signal generator
A calibrated source of RF at a precise frequency and level, often with modulation, for aligning and testing receivers and RF stages.
Where a scope shows voltage vs. time, a spectrum analyzer shows amplitude vs. frequency — it displays a signal's magnitude and frequency, revealing the carrier, harmonics, and spurious signals you can't pick out on a scope. Essential for RF and EMI work.
| Tool | What it does |
|---|---|
| Logic probe | Indicates digital high / low (and pulse) logic conditions at a point — a quick go/no-go for logic levels without a scope. |
| Analog VOM | Volt-Ohm-Milliammeter with a moving needle. Lower input impedance than a DMM; still useful for watching trends a digit display hides. |
| LCR meter | Measures inductance, capacitance, and resistance precisely — for characterizing reactive parts. |
| Frequency counter | Displays an exact frequency by counting cycles over a precise time gate. |
| Bench power supply | Provides adjustable, current-limited DC for powering circuits under test. |
Measurements are only trustworthy if the instrument is. Equipment is periodically calibrated against a known standard; an out-of-cal meter gives confident, wrong answers. Respect input limits (voltage and current ratings), use the correct probe and range, and account for the instrument's own effect on the circuit. A reading only means something compared to the expected value from the schematic.