1771 IFE fluctuating read.

plchacker · Sep 18, 2012

Hi all, it has been a while.

OK, I am setting up a process trainer with a 5/40E in an 8 slot chassis set up to single slot addressing. All is good so far. Group 4 in Rack 0 houses a 1771-IFE series A.

This is not my First run in with the old IFE modules. I have successfully set up many of these in the past.

It is set up for differential inputs. (Personal preference)
It is set up for 4-20mA. 0-4095. (Temporary until I get it working correctly)
It is set up for 2's complement.

LAD 2 has a single rung, JSR to LAD 3 which contains the BTR and BTW instructions for the three analog cards in the chassis.

The very first thing I did in this project was to set up the I/O config, and from there set up the cards/Logic for the cards. So there should be no corrupt data. Nothing in the program to interfere with the inputs/block transfers etc.

So the card works, I get a signal that fluctuates slightly when connected to a loop calibrator. Not as steady as I would like but not bad.

Next step, connect a Rosemount 3144P Temp Transmitter, (J-Type thermocouple) and 24VDC power supply. As soon as I powered up, and set up the transmitter the input started jumping wildly from 0 to a little over the signal value.

I do not have the empty channels shorted to common, as I have not yet connected all of the inputs I plan to use. Still, I have never seen a signal jump around like this.

The actual 4-20 signal is as steady as a rock.

I suspect noise, but at this point the PLC/Cabinet is pretty bare. The only I/O connected is the single transmitter to the IFE card. Any suggestions?

OkiePC · Sep 18, 2012

plchacker said:
Hi all, it has been a while.

OK, I am setting up a process trainer with a 5/40E in an 8 slot chassis set up to single slot addressing. All is good so far. Group 4 in Rack 0 houses a 1771-IFE series A.

This is not my First run in with the old IFE modules. I have successfully set up many of these in the past.

It is set up for differential inputs. (Personal preference)
It is set up for 4-20mA. 0-4095. (Temporary until I get it working correctly)
It is set up for 2's complement.

LAD 2 has a single rung, JSR to LAD 3 which contains the BTR and BTW instructions for the three analog cards in the chassis.

The very first thing I did in this project was to set up the I/O config, and from there set up the cards/Logic for the cards. So there should be no corrupt data. Nothing in the program to interfere with the inputs/block transfers etc.

So the card works, I get a signal that fluctuates slightly when connected to a loop calibrator. Not as steady as I would like but not bad.

Next step, connect a Rosemount 3144P Temp Transmitter, (J-Type thermocouple) and 24VDC power supply. As soon as I powered up, and set up the transmitter the input started jumping wildly from 0 to a little over the signal value.

I do not have the empty channels shorted to common, as I have not yet connected all of the inputs I plan to use. Still, I have never seen a signal jump around like this.

The actual 4-20 signal is as steady as a rock.

I suspect noise, but at this point the PLC/Cabinet is pretty bare. The only I/O connected is the single transmitter to the IFE card. Any suggestions?

Follow the grounding and shielding requirements for this one and go ahead and put jumpers on the unused channels. I have seen this help with noise.

The noise I had was on a 0-10vdc signal. I have not had issues with 4-20mA noise, but an intermittent open circuit can be the root cause. The filter time and overall conversion speed of the channel may come into play, but you measure it as steady, so methinks you gotta bad channel.

To divide and conquer, you need to connect that same set up to another channel to eliminate a potentially flaky analog input channel in the card.

Also, if you zip and post the code, someone can look at the logic to make sure nothing funky is going on with the configuration. I have seen battling BTWs cause problems...you don't need to reconfigure the card every scan or every other scan, but if you do, make sure you control the data being sent rigorously. I always trusted the card to request config bit, and the PLC 1st scan bit to send the BTW config and have a manual method in parallel in case someone needs to play musical cards...

EDIT:

Mickey said:
Do that and report back.

Edit: OkiePC types faster then I do.

OkiePC Edits faster and more frequently...

Mickey · Sep 18, 2012

I do not have the empty channels shorted to common

Do that and report back.

Edit: OkiePC types faster then I do.

Ron Beaufort · Sep 18, 2012

just as a suggestion, see if this helps ...

try connecting a "bleeder" resistor from the low side (negative) terminal of the input channel to ground ... something like 100K ohms should be OK ...

so - if you're connecting to Channel 1 (the first channel) on the module, then connect the bleeder to terminal number 2 - and then to ground ...

plchacker · Sep 18, 2012

OkiePC said:
Follow the grounding and shielding requirements for this one and go ahead and put jumpers on the unused channels. I have seen this help with noise.

The noise I had was on a 0-10vdc signal. I have not had issues with 4-20mA noise, but an intermittent open circuit can be the root cause. The filter time and overall conversion speed of the channel may come into play, but you measure it as steady, so methinks you gotta bad channel.

To divide and conquer, you need to connect that same set up to another channel to eliminate a potentially flaky analog input channel in the card.

Also, if you zip and post the code, someone can look at the logic to make sure nothing funky is going on with the configuration. I have seen battling BTWs cause problems...you don't need to reconfigure the card every scan or every other scan, but if you do, make sure you control the data being sent rigorously. I always trusted the card to request config bit, and the PLC 1st scan bit to send the BTW config and have a manual method in parallel in case someone needs to play musical cards...

I tried the next channel down, same results. I'll have to wait till the morning to short the empties. I'll likely connect the other transmitters before doing that. (Even if the card is bad, the swing arm will be ready.)

I quit using 0-10 quite a while back for several reasons. This is going to be a pretty simple trainer. RSView32 will be doing most of the work, along with the dreaded PID instruction.

I don't have an extra card on hand, or I would have swapped it out by now.

Bifocals are no fun with the jumpers.// I had students check behind me to make sure they were right.

More in the morning.

plchacker · Sep 18, 2012

Ron Beaufort said:
just as a suggestion, see if this helps ...

try connecting a "bleeder" resistor from the low side (negative) terminal of the input channel to ground ... something like 100K ohms should be OK ...

so - if you're connecting to Channel 1 (the first channel) on the module, then connect the bleeder to terminal number 2 - and then to ground ...

Got it, will try that too. I was wondering if that would make a difference.

This a a clean, new cabinet. No noise in the area other than a CLX chassis/PanelView about ten feet away. It is late.

Hope all is well Ron.. It's been a while.

OkiePC · Sep 18, 2012

plchacker said:
I tried the next channel down, same results. I'll have to wait till the morning to short the empties. I'll likely connect the other transmitters before doing that. (Even if the card is bad, the swing arm will be ready.)

I quit using 0-10 quite a while back for several reasons. This is going to be a pretty simple trainer. RSView32 will be doing most of the work, along with the dreaded PID instruction. I don't have an extra card on hand, or I would have swapped it out by now.

Bifocals are no fun with the jumpers.// I had students check behind me to make sure they were right.

More in the morning.

Don't omit the big green wire to the swingarm rod (I may be thinking of the OFE, rtfm...).

And since it's a trainer, you could lie to it (filter in PLC code) especially if its stable most of the time...this could impact any PID logic relying on that signal though...

plchacker · Sep 19, 2012

OkiePC said:
Don't omit the big green wire to the swingarm rod (I may be thinking of the OFE, rtfm...).

And since it's a trainer, you could lie to it (filter in PLC code) especially if its stable most of the time...this could impact any PID logic relying on that signal though...

The temp is just a show and tell, however, I will be controlling Level, with two diaphragm valves. (In and Out)

Next week we will be showing it and the Tic Tac Toe robot to about 5-7K eighth graders.

The Robot is pretty cool, by far the best fast turn around project here at the school. But I wanted to step it up a notch this year.

plchacker · Sep 19, 2012

OK Got it. It must have been noise. I'm back to channel 1 and everything is working great. We wired with good quality shielded twisted signal cable. Grounded the shields at the PLC end, and all is well. It is 74F in the room right now. The trainer is looking great. 42" TV mounted, and RSView doing its deed.

Thanks guys.

The PLC5 was sitting in a cabinet all lonely and pretty much dead. Now she is purring along. It is good to see old friends back in the game. CLX is cool enough, but the PLC5 is still functional and worth the effort, if not the price.

1771 IFE fluctuating read.

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