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⌚Timestamps:
00:00 - Intro
00:37 - Step 5) Test the PLC analog inputs
01:22 - Signal simulator
01:49 - PLC card manual
04:22 - Step 6) Test the PLC analog outputs
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In the previous video, you learned how you can test your PLC digital input and output.
In this final video, you’ll learn how you can easily test your PLC analog inputs and outputs.
Step 5) Test the PLC analog inputs
As for the next step you need to test the analog inputs. To do this, you simply need to know the type of input signal that will be connected to your PLC analog input.
Typical input analog devices are transmitters, RTDs, and thermocouples, each providing different signals to the PLC. Transmitters typically send a 4-20mA signal, RTDs produce a variable resistance, and Thermocouples produce a very small millivolt signal.
To test the analog input card and wiring in your control panel, you need two things:
1. A signal simulator
2. The wiring diagram of the control panel
Simulators are capable of giving you signals that are produced by transmitters, RTDs, and Thermocouples.
For example, let’s say that our analog input card will receive 4-20 mA input signals from transmitters installed in the field.
To test this input we first need to know how the transmitters are connected to the card. This is what you should already have on your wiring diagram.
The other way to check the wiring diagram for your card is the manual. For example, this is the wiring diagram for the analog input card that I have installed in my control panel.
All you need to know here is that if you want to wire a 2-wire transmitter to this card you simply need to connect the positive to terminal number 1 and the negative to the next terminal. The wiring is the same for the rest of the 2-wire transmitters.
Assuming that other ends of these terminals here are connected to terminals number 1 and 2, to test this input I can put the signal simulator on the 4-20mA current mode and then connect it to the other end of these terminals.
By doing this, I am simulating a 2-wire transmitter connected to my analog input card. Now I can play with the simulator, change the input values and observe the changes on the output based on the PLC logic.
For example, let’s say that this is a pressure transmitter that is used to measure the oil pressure in the system. Based on the PLC logic, if the oil pressure goes under a certain level the oil pump needs to turn on.
To test this I can change the current and look at the HMI installed on the panel to see if the indicator for the oil pump turns on. If the pump turns on it means that everything works fine for this input and the logic. If the oil pump does not turn on, I need to look into the wiring or my PLC logic.
Now you may ask, what If I don’t have an HMI installed with my panel? How can I see the change in the output?
To check if the pump turns on in the output, you just need to know to which digital output the pump will be connected to and then you can see if the relay or the contactor will be energized as you change the input current.
Step 6) Test the PLC analog outputs
Ok, the last step is to test the analog output card. The testing process here is pretty similar to what we did for the digital output card. For each analog output we can simulate a signal in the input and then check if the analog output changes based on what we expect in the PLC logic.
An analog output signal could be either voltage or current. We can measure this using a simple digital multimeter as well. Most of the signal simulators can also be used to perform measurement functions similar to a digital multimeter.
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To learn more, you might want to review these videos:
How to Wire Sensors to a PLC - Part 1 • How to Wire Sensors to...
How to Wire Sensors to a PLC - Part 2 • How to Wire Sensors to...
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