Factory Acceptance Test Explained - Part 2 | PLC Digital I/O Test

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⌚Timestamps:

00:00 - Intro
01:29 - Simulated signals
01:59 - Step 3) Test the PLC digital inputs
03:31 - Passive and active devices
04:25 - Step 4) Test the PLC digital outputs

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When performing a FAT for a control cabinet that includes a PLC, one of the most important things to test is the PLC inputs and outputs.

Depending on your application, you may have different input and output cards for your PLC.

To do a FAT you need to test each of the PLC inputs and outputs one by one and make sure everything works properly based on the PLC logic.

But you may ask “how can I do this while the control cabinet is still not installed on the site and there are no actual sensors or actuators connected to it?”

The answer to this question is simulated signals. You need to use simulated signals to perform your Factory Acceptance Test.

Step 3) Let’s start with the digital inputs first. The PLC digital inputs are connected to the upside of DI terminals. The other side of the terminals will be connected to the switches and sensors once we take the cabinet to the site.

But since we have some switches on the control cabinet door such as a mute buzzer, ESD Reset, and Emergency Stop, we have already wired these input devices to the other side of the terminals and we already have them connected to the relevant PLC digital inputs. Let’s start our test with these switches first.

We’ll start with the mute buzzer input. Let’s say that this push button is connected to the first digital input of the PLC. To test this input, all you need to do is to press the push button and see if the LED light for the first digital input on the card turns on.

If the LED does not turn on when you press the push button, it means that there is something wrong with the wiring.

In this case, you need to take the panel wiring diagram and follow the wiring on the panel and fix the issue.

Moving on to test the rest of the PLC digital inputs, if the device that will be connected to the digital input is passive, like a simple switch, you can simulate the signal by connecting a piece of wire to the terminal blocks.

However, if the device is active, you need to look at the wiring diagram and find the best way to simulate the signal coming from that active device.

In most cases, you can make use of a simulator. A simulator is a device that can accurately reproduce a sensor output.

Step 4) After you’re done with testing the digital inputs, you can move on to testing the digital outputs. The digital output card that we have sends a 24-volt signal to various devices connected to individual output terminals.

A digital output could be connected directly to an output device like a buzzer or a relay that could operate an actuator like a motor.

To test each output we just need to give the PLC an input signal and see if the digital outputs change as expected based on the PLC program.

The first digital output that we have here is connected to a motor via a contactor. The PLC program logic, says when the level switch 1 and level switch 2 are both active, we need to have the motor connected to this output turned on.

To test the output, all you need to do is to activate the inputs using simulated signals and see if the contactor on the output will be energized.

If the contactor is energized, it means all the wiring and the PLC logic works perfectly fine for this output. If not, you need to review your wiring using the wiring diagram.

You can do the same to test the rest of the PLC digital outputs.

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To learn more, you might want to review our other articles:

What is an Instrument Calibrator? https://realpars.com/instrument-calib...

How to Follow an Electrical Panel Wiring Diagram https://realpars.com/panel-wiring-dia...

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