Testing A/B Outputs

[Guest dunbarbe]

Does anyone have a way to test A/B Outputs to see if they are operating correctly? In the past I have found that an output LED shows that the output is operating but there is no current flow (aside from the obvious where the output doesn't operate.) I would like to have a way to test the outputs so that I can avoid system down time. Thanks.

[Guest Guest]

I'm not quite sure about the scenario you describe, but one method I'd try is connecting a 240 ohm, 2 watt resistor from the output to ground (or 0vDC, if an isolated system), assuming 24vDC supplies. If the output LED is on, then the output should supply a MINIMUM of 100mA, which would generate about 23-24v DC across the resistor (to ground or 0vDC). Some of the A-B PLCs can turn on the output LED but not the output, like under forced conditions or if the output group on the card is not wired.

[panic mode 246]

Output LEDs and not good indicator if the output device is really working or not. It only indicated that PLC is trying to drive that output. Maybe there is nothing wired to that output... Testing output alone is not complete test. Even if output is used but something else is wrong, you should see if turning output on/off results in proper action. For example you could have swapped airlines on the cylinder or manifold, sensors swapped around, mechanincal jam on the machine etc. I always use manual mode of my program to test I/O (inputs AND outputs). It is much more convenient to use touchscreen buttons than to mess with datatables. In fact that is part of service routine for our customers (it is documented in our manuals). There is always fault handling routine that checks for motion timeouts, failed sensor toggles, etc. Hope this helps...

[Guest dunbarbe]

I'm relatively new to this so I hope this isn't too stupid of a question....heh. How do you test in Manual Mode? And once selected, are changes made the same way that, say forces are made? Thanks.

[panic mode 246]

Create your own auto/manual/step mode and once the program is downloaded to controller, start machine, switch to manual mode and try each output. Following is very simple example of how solenoid outputs could be controlled. Note that this is very basic and generic form.