Need Help for A/B SLC 500 - troubleshooting tips 1

[LEEtheV]

I have an SLC500 with a 1746 analog controller..I'm using it to control a safety circiut by measuring 4-20 DC Ma from both a RTD and a pressure transducer with points from an enthapy curve plotted (Rockwell software) to reflect the safe zone for vaporization of C3H8 (propane)....This programming was done by others and now I have to verify the integrity og the programming..((i.e. How can I force inputs (by plugging in numbers? where ?) to test the ladder software ?)...Exactly: The inputs are N7:4 and N7:10 with the card in the #2 slot....This will also help me to bench test systems without transmitters installed.....Any help would be much appreciated...Lee

 

[wde3477]

The quick-n-dirty way would be to put a MOV block immediately before the rung to be tested, moving a value into N7:4 or N7:10. By using a spare integer (N7:??) for the source data, you can then go into the data block and dynamically change the value that will be written into N7:4 or N7:10.
Another way would be to put an AFI in the rung (a BTR block?) that reads the card and puts the value into N7:4 or N7:10, then you can change N7:4 or N7:10 directly, however, no other inputs on that card will be valid while the AFI is in place.
I would caution you to thoroughly check the program for multiple uses of those variables, or to have the propane system properly secured so that no unexpected actions take place while testing.

 

[LEEtheV]

I want to thank you VERY much for replying....Over the last 2 days, I've crash coursed my way to remembering the A/B course I took over 3 years ago (and very rarely used it)and also applying that to the 4.0 version...Anyway, I was really stumped that I had 24V going to both transmitters and nothing was coming back...I knew the transmitters were ok....Further wire tracing revealed that the installer of this new SLC (last week because the old one was zapped by a power spike) reversed the DC power to the transmitters...(i.e. he put the wires he took off the old SLC on backwards to the new one...The Analog transmitters will ony give a DC Ma signal back unless the polarity is correct...I simply switched the wires, cleared the processor and re-booted the system with an EEPROM that had the correct software...The output channel latched and the solenoid opened at correct set points ....Thought you might be curious...Thanx, again...LEE