You test it almost like a switch: power it with the right voltage, then watch the output change on your multimeter when something comes close. The exact wiring depends on the type of proximity sensor you have.
I’ll walk through the common cases.
1. Before anything: identify what kind of sensor you have
Look at the body/label:
- Markings like “10–30 V DC” → DC sensor
- Markings like “NPN / PNP, NO / NC” → 3-wire DC sensor
- Only two wires labeled “L / N” or “+ / –” → 2-wire sensor (acts like a switch)
- Markings like “0–10 V” or “4–20 mA” → analog output sensor
Also note wire colors on typical DC industrial sensors:
- Brown = +V
- Blue = 0 V (GND)
- Black = output (sometimes white is another output)
2. Testing a 3-wire DC proximity sensor (most common)
Goal: power it, then see the output voltage change when metal/target is near.
2.1 Wiring
You’ll need a DC supply in the allowed range (e.g. 12 V or 24 V).
- Connect power
- Brown → +V of supply
- Blue → 0 V (GND) of supply
Set multimeter to DC Volts (V⎓)
Connect the meter
- Black meter lead → sensor blue (GND)
- Red meter lead → sensor output wire (usually black)
- Power on the supply.
2.2 Read the output (NPN vs PNP)
Check your label:
Case A: PNP, normally open (PNP NO)
- Target far: output ≈ 0 V
- Target near: output ≈ supply (e.g. ~12 V / ~24 V)
Case B: NPN, normally open (NPN NO)
- Target far: output ≈ supply (pulled up internally) or floating around that value
- Target near: output drops close to 0 V (sensor sinks current to ground)
So while watching the meter:
- Hold a metal object (inductive sensor) or target (capacitive/optical) near the sensing face.
- You should see a clear jump in the output voltage between “far” and “near” states.
If the sensor has an LED, it should toggle at the same time as your meter reading.
If you don’t see any change:
- Double-check you didn’t swap brown/blue.
- Make sure the supply voltage is within the rated range.
- Try flipping the target closer/ farther a few times and give it a second.
3. Testing a 2-wire proximity sensor (acts like a switch)
Many 2-wire prox sensors behave like an electronic switch in series with the load.
Simple continuity-style test (low-voltage DC type only)
⚠ Don’t do this if the sensor is rated for 230 V AC mains unless you know exactly what you’re doing. Use a low-voltage bench supply instead.
- Set your meter to resistance or continuity (beep).
- Connect meter leads to the two sensor wires.
- Move your target near the sensor:
- NO (normally open) type: resistance goes from “open/very high” → “low” when triggered.
- NC (normally closed) type: resistance goes from “low” → “open/high” when triggered.
For higher-power or AC types, better:
- Put the sensor in series with a small load (lamp or resistor) and a suitable supply.
- Measure voltage across the sensor or load with the multimeter as you bring the target near/far.
- You’re looking for a clear ON/OFF behavior.
4. Testing analog proximity sensors (0–10 V or 4–20 mA)
4.1 0–10 V type
- Wire brown → +V, blue → GND.
- Set multimeter to DC volts.
- Measure between output and GND.
- Move target closer/farther → voltage should sweep somewhere between 0 and 10 V (or the specified span).
4.2 4–20 mA type
- Set multimeter to mA range.
- Break the loop and connect the meter in series:
- Supply + → sensor +
- Sensor – → meter +
- Meter – → supply –
- Move target → current should change between ~4 mA (far) and ~20 mA (near).
5. Common mistakes to avoid
Wrong supply voltage
Don’t feed a 10–30 V DC sensor with 5 V and expect it to work; also don’t put 24 V on a 5 V part.Measuring current in the voltage jack
When measuring current (mA) you must move the red lead to the mA jack and set mode accordingly.Forgetting the ground reference
Always measure output relative to the sensor’s GND (blue wire), not relative to some random ground.Trying to test an AC mains sensor directly on 230 V without experience
Use isolation and proper safety gear, or test it instead with a designed test circuit or lower-voltage bench setup if the spec allows.
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