Voltage on 1771 OAD in PLC-5

okiebob

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Join Date
May 2002
Location
McAlester, OK
Posts
98
I am currently setting up a Nasty Labs Field Point as a test set to the 1771-IAD OAD and IXE mV cards in my PLC-5 chassis. My problem is that the OAD channels are reading 65 VAC to 73 VAC. I am wired 115 120 VAC to terms A_B_C_D and common to C at bottom, out channels to FP DI (discrete input) to common. The 65-73 is being read as an out by the FP DI thus lighting the psuedo (software lite), what I want to do is reduce the "strays" to below 14 V, I have already tried a shunt in parallel with the LOAD (FP DI) to no avail. I have also tried removing the OAD common and no joy again. Any tips on this Thanks guys Little Bob
 
Say it ain't so

That would work if I could manage it, But the "lights" are actually just part of a GUI in the software, Thats why I need to reduce leakage to <14 VAC, the circuit actually does function for operation, ie testing the ladder, but the testing simulation just doesn't look right with the extra lights lit when they are not supposed to be. Maybe a little uptight but in the end this will help with other projects and plus make the simulation (with an audience) go over very well. The audience being the actual system operators and maintenance people as we want as much VALID input from them as poss and to keep things as SIMPLE as poss at the same time (no brother in law circuits) commented code and full documentation.
 
The SIMULATOR

The simulation HMI is a Laptop, the lights are software driven, on the pc (graphics) drop and drag setup very nice, just a little sensitive to strays leakage, I was hoping to pull down V enough, I already tried the 39K 1W recommended by AB, so JOHN P it looks like I may have to use the GP Relay to DEMO with. I'll keep pluging away in the meantime maybe the answer will reveal itself. Thanks Ron B, Have a good weekend.
 
I had a somewhat similiar problem the other day. The input to the card was triggering on with "Stray" voltage. We tried using a small DIN rail mounted isolation relay that had an LED to indicate that it was energized. It was lighting the LED even if the relay was not energized. The relay worked correctly except for that. The "stray" voltage was around 50 - 60 VAC. The stray voltage, I think, was being induced because the wire for the coil was in a multi-conductor (40) cable about 200' long. The only solution was to use a standard (ice-cube) type relay. I also put a device called "Quench-Arc" suppressor in parallel with the relay coil.
 
Leakage

If the leakage is not acceptable change to the 1771-OW type of module.

In trying to work with the leakage change your pilot lights to full voltage incadecent type.
If you want zero leakage then use the proper module.
Roger

jrwb4gbm;
That 50-60 stray volts don't sound like induced voltage, sounds more like voltage bleeding over.
Do a current test on it by placing an incandescent bulb between that wire and ground. Induced voltage should not keep the bulb burning.
If it is induced voltage you should be able to stick it directly to ground and the voltage will dissipate, no harm no foul.(I'm not suggesting that you do that.)
Roger
 
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