CLX Analog Inputs Wildly Fluctuating

[Secpcb]

I don't have a lot of experience with Studio5000, years with SLC's and PLC5's and started on PLC2's.

My present new project is a 1756-L73 using Studio500 v33. The 10 slot rack has 2 fast analog in/out cards - 4 in 2 out each. 1756-IF4XOF2F, Ser A Rev 1.001

Still on the bench programming and testing, but I have a big problem with the analog inputs, I have not tested the outputs yet.

With a signal from signal conditioners and the mA monitored with a calibrator the mA to the inputs is consistent and may only fluctuate 0.02 mA at the most, however online with the CPU running the it runs wild. The inputs are set to range from 0 to 20000, I have a scaling AOI and added a dampening AOI.

With the mA input staying the same, if the scaling changes it to temperature from 32 to 212°F the temperature should stay at 75°. However, even with dampening, the 75 drops to as low as 36, up to 60, down to 40, up to 75, down to 42, etc. It never goes over 75, and never drops to 32 or below.
EDIT: the raw inputs from the analog cards fluctuate, not caused by the Scaling AOI.

I have double checked the wiring per the manual and moved the input to the other card and other inputs.

On the module configs I have: (for all 8 inputs)
RTS: 2.00 ms
Synchronize Module Inputs NOT checked
Input Type: Current (mA)
Input Range: 0mA to 20mA
High Signal: 20.0000
Low Signal: 0.0000
High Engineering: 20000.000
Low Engineering: 0.0000
Digital Filter: 0.00 ms

Is it possible I have some setting wrong? Is there a default setting I haven't changed?

 

[rupej]

This may not be the most helpful, but every time I have experienced something like this, it was a wiring problem. Sometimes the DC com points are confusingly labeled in the manual. Can you draw a quick diagram of how you have the card wired?

 

[JTCat]

Hi,

More information is required.

I am having some difficulty understanding what the conditions of operation are.
What are the field devices? The sensors being used? The loop method being used? Closed? Open?

You are able to test it on a bench using a signal generator without any problems?

When you are using your field devices you are encountering problems?

It is your raw input data that is fluctuating wildly?

Does it fluctuate when using the signal generator? Or only when connected to the field devices?

Can you hook up a signal generator to one input channel and have the field devices hooked up to the others and see if the signal from the signal generator is steadier than the field devices?

Have you hooked up a multimeter in line with one of the field devices and verified the signal?

These are some troubleshooting steps you can follow to start ruling things out.

You may have a wiring issue. You may have a noisy field device. You could have an issue with a PSU as well.

Start isolating things one by one. Analog issues can be tricky to find

 

[Secpcb]

Right now it is on the bench. No sensors connected. I am using PR 4114 signal conditioners as the signal generators.

I have tried the scaling as temperature and pressure.

The raw inputs <Local:8:I.In[0].Data> are fluctuating when the signal conditioner output (I have a digital programming unit on it with a display) and a mA calibrator show a steady current.

Shielded cable grounded at one end and it is only a few feet long on the bench, no where near any power cables, even 120V.

2 setups going to an input on each card doing the same, and moving to another input the fluctuating continues - all 8 inputs act the same.

I have gone through the 1756 ControlLogix Specifications 1765-TD002K-EN-E for wiring and config but don't see what I am missing. I am wiring the + to +IN-1/V and IN-1/1 as shown and have tried disconnecting the lead to the Voltage. Page 39 of the manual.

 

[Secpcb]

Wired exactly as shown in the manual:

 

[Secpcb]

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[JTCat]

Hi,
do you have this wired for voltage mode?

Remember, for 2 wire field device 4-20 ma devices, you wire the negative of the field device to the positive of the input card, then the negative of the PSU thats powering the field device to the negative of the negative on the input card.

Hook up a 2 wire device and see if the problem goes away.

 

[Secpcb]

No, these are wired for the mA signal as shown on the left of the photo.

It is a 2 wire output from the self powered signal conditioners, and per the manual the + needs to be connected to both input terminals. I have tried disconnecting the voltage input. The 24VDC switching power supply powering the signal conditions has been checked with an oscilloscope, while disconnected and while running. to make sure it is not providing some interference or dirty input.

 

[JTCat]

Hi,
Please try wiring a temperature sensor or another such 2 wire device into the analog input card and see if you still have the issue.

 

[Secpcb]

Hi,
Please try wiring a temperature sensor or another such 2 wire device into the analog input card and see if you still have the issue.

I will try that, but the mA calibrator shows a steady current into the inputs now, just the reading fluctuates.

I still think I don't have something set correct that I don't see or know about.

 

[Mickey]

Have you tried putting a jumper across unused channels?

 

[Secpcb]

Have you tried putting a jumper across unused channels?

That I have not tried, that suggestion is not in the manual. Also the disconnected inputs all read 21000 value consistently, but they might interfere so I will try that.

 

[thingstodo]

I don't have a lot of experience with Studio5000, years with SLC's and PLC5's and started on PLC2's.

My present new project is a 1756-L73 using Studio500 v33. The 10 slot rack has 2 fast analog in/out cards - 4 in 2 out each. 1756-IF4XOF2F, Ser A Rev 1.001

Still on the bench programming and testing, but I have a big problem with the analog inputs, I have not tested the outputs yet.

With a signal from signal conditioners and the mA monitored with a calibrator the mA to the inputs is consistent and may only fluctuate 0.02 mA at the most, however online with the CPU running the it runs wild. The inputs are set to range from 0 to 20000, I have a scaling AOI and added a dampening AOI.

With the mA input staying the same, if the scaling changes it to temperature from 32 to 212°F the temperature should stay at 75°. However, even with dampening, the 75 drops to as low as 36, up to 60, down to 40, up to 75, down to 42, etc. It never goes over 75, and never drops to 32 or below.
EDIT: the raw inputs from the analog cards fluctuate, not caused by the Scaling AOI.

I have double checked the wiring per the manual and moved the input to the other card and other inputs.

On the module configs I have: (for all 8 inputs)
RTS: 2.00 ms
Synchronize Module Inputs NOT checked
Input Type: Current (mA)
Input Range: 0mA to 20mA
High Signal: 20.0000
Low Signal: 0.0000
High Engineering: 20000.000
Low Engineering: 0.0000
Digital Filter: 0.00 ms

Is it possible I have some setting wrong? Is there a default setting I haven't changed?

I noticed the Digital filter is 0.00 ms. Running from memory for other (and slower) cards ... the digital filter is either 8.33 ms or 16.66 ms to filter out your AC power.


That said, you are running at 2 ms, so I'm not sure that the filter will work for you. And you are running 4 - 20 ma not voltage ... and you have shielded cables .. so it should not be a problem.


But if you want to try something else, it can't hurt to try it.

 

[Ron Brown]

If you are using the current setup do not wire up the IN V, I have had odd things happen when I connected to both voltage and current input terminals. Just use the current input if you are using a current signal.