PLC5 in "Test Mode"

I have a question about PLC5's. I went online with one processor and it was in "Remote Test Mode". I don't know who put it in test mode or how it got placed in test mode, but it was. The question I have is what does test mode do to the processor and does it still allow the program to run? The program doesn't have any direct I/O, all it does is read/write through serial and ethernet.

Could someone give me a good desciption of what test mode actully does and what one would use it for?

Thanks,

Scott

basic idea: the processor scans the ladder logic but it does NOT "fire" the real-world outputs ... many people consider this to be the "dry-fire" mode - sort of like snapping a pistol with no ammunition in it ... the "supposed" advantage is that you can test the operation of your program without actually energizing anything in the field ... sounds like a good idea when you're commissioning a new system ... but in practice, the possibility exists that you could have some outputs "miswired" ...

example: during the "test" the screen tells you that the ALARM_LAMP is being turned on ... looks good - that's the operation that you want ... unfortunately the electrician got a couple of the wires reversed ... so ... when you finally get around to the actual RUN mode, you don't energize the ALARM_LAMP ... maybe you energize the HYDRAULIC_RAM instead ... OOPS! ...

personally I think that the TEST mode is overrated ... it's OK as long as you fully understand its limitations ... just don't trust everything that it tells you ... you STILL need to take other steps to confirm that each PLC output (and input) properly matches the wiring in the field ...

The program doesn't have any direct I/O, all it does is read/write through serial and ethernet.

Click to expand...

since your system doesn't have any I/O to control, the TEST mode is PROBABLY giving you exactly the same operation as the RUN mode would give you ... but (everything else being equal) most people would just go ahead and put the thing in the RUN mode and get on with their lives ...

Thanks for the clarification Ron.