PLC Panel Contintuity Tester

Question

I'm trying to build a simple Unistream PLC panel continuity tester, I'm simply struggling to understand how PLC works and create a simple continuity tester for it.

The test jig simply provides 24V to the Unit Under Test(PLC Panel) and the PLC panel output (sampling level sensor) would be tested if all connections leading to the connector have continuity.

Continuity Test A: Simple continuity test to see if 24V is being supplied to the PLC. It checks the 3 wires of the level sensor connector. LT11-24V LT11-GND LT11-OUT All three wires need to be tested so as you can see in the photo. The SPDT switches from LT11-OUT to LT11-GND. will PLC let the LED light up or would it be too low of a current to light up a 24V LED?

Continuity Test B: Here I've done a little research of how PLC works and to my understanding the common terminal(CM0) of the I0 to an 24V to be in a Source Mode as seen in the PLC data sheet image.

Basically, I'm just asking how should do a continuity of test I/O of the PLC?

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Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Test circuit schematic.

How it works

• J0 to J3 are your test connectors.
• X0 to X3 are your test indicators. These will test supply on pins 1 and 2. Add a diode to each if you want it to light only when the correct polarity is applied.
• SW0 to SW3 will ground each of the source-configured inputs. If there are input indicator lamps on the PLC the corresponding indicator will illuminate as each button is pressed.

Notes:

• Schematic is right way up.
• Schematic reads from left to right.
• Where possible, higher voltages are on the top and current flows from top to bottom.
• Schematic symbols are used, not cartoons.
• The layout is organised so that the schema (circuit intent) is very clear.