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Old August 2nd, 2005, 06:54 PM   #1
Terry Woods
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Terry Woods is offline
 
Join Date: Apr 2002
Posts: 3,170
OPTO22 Question

Fastjim sent the following PM to me...

Quote:
Originally Posted by fastjim
Hello Terry,

I am working on an OPTO22 equipment and will be very pleased if you should help me.

I need to do a built-in-test (or autotest) on the equipment.

The goal is to connect a maintenance laptop and execute a program which give me the "hardware statement" of the OPTO22, detect any power supply problem, network problem, ...

I don't know if there is any software solution or if I have to develop a specific solution (Visual Basic or Visual C++)

Thank you very much

Best regards,

Jim.

Hi Jim,

You said...
"The goal is to connect a maintenance laptop and execute a program which give me the "hardware statement" of the OPTO22, detect any power supply problem, network problem, ..."

What exactly is the primary controller on the system?

PLC? Or what? Please provide as many details as you can.

The following is a full-blown "Shadow Watcher/Controller". Use it to the extent that you consider reasonable.

I should think that you would want to know the status of the outputs from the controller AND the status of the OPTO Output Modules.

The controller might be "telling" the OPTO Output to turn ON, but the OPTO Output might actually be OFF. This simple observation is a good "positive test" indicating that the OPTO Output has failed into the Open (Always OFF) status.

The controller might be "telling" the OPTO Output to turn OFF, but the OPTO Output might actually be ON. This is another simple observation, a good "positive test", indicating that the OPTO Output has failed into the Closed (Always ON) status.

Now, even though the controller might be "telling" the OPTO Output to turn OFF, and the OPTO Output is OFF, that is NOT sufficient verification that the Output Module is operating properly. And, even if the controller might be "telling" the OPTO Output to turn ON, and the OPTO Output is ON, that also is NOT sufficient verification that the Output Module is operating properly.

You need to exercise the output (ON/OFF) to verify that it follows commands from the controller. Only then can you "KNOW" that the OPTO Output is working properly.

To do this, you need to be able to "see" the control signal going to the module, AND the signal from the output module. You need to verify that the module follows the command signal. You also need to take into consideration the possibility of a Normally Closed Output from the module.

You will need to be able to control the actual output signal from the controller to the OPTO Output Module. You need to be able to do so from your laptop. In most cases, as long as the process is stopped, you should be able to exercise a particular output signal without causing any subsequent actions in the process.

Now, having done all of that, you have only verified that the OPTO Output Modules operate as commanded. This does very little to verify the code... except in the result. That is, even though results might be occurring as expected... they might or might not be occurring for the correct reasons. This determination depends on your understanding of the controlling code.

The same applies to Inputs.

You need to "KNOW" what signals are being applied to the OPTO Input Modules AND what signals the controller is "seeing" from those modules.

All of the above requires a means of "Shadow Watching"... that is, "Watching from the Shadows". Typically, this means extra wiring. It also means, having a place to read the information that the "Shadow Watcher" collects. This can be most easily accomplished by means of a set of Opto-Isolators.

Your "Reader" (laptop) would need to "read" the states of the Opto-Isolators. One set of Opto-Isolators would read the states of the Output Modules (Control Signal & Controlled Signal). Another set would read the states of the Input Modules (Field Signal and the OPTO Input Module output signal).

Your "Reader" must be capable of providing, simulating Field Input signals to the input side of the Input Modules.
Your "Reader" must be capable of providing, simulating Controller Output signals to the input side of the Output Modules.

Now, as far as how to actually accomplish all of this... including power supply and network issues, it depends on your answers to the questions I posed.

PS...
Another thing you need to be aware of is that OPTO Modules provide built-in indicators on each module indicating the status of the field Input Signal or the Controller Output Signal. If you are willing to perform actual troubleshooting at the device level (at input/output module level) then all of the above is for naught.
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