Problems with UIA-0800N analog input modules

[Fluidpowerman]

Working on a project with several UIA-0800A analog input modules.    We are using all 4-20 ma transducer input.  Pressure, Flow, Weight(load cell), pH.  the only difference is

for some of the transducers we power the loop thru and external power supply (24VDC) for the pressure transducers.  results are solid.  Others the loop power is provided by the 

transducer.  For example for the Load cells the scale provides an 4-20 ma output signal with loop power to the UIA-0800A.  What is very strange is the input signal floats around 

at a slow steady pace.  including going below 4 ma.   at first the number will appear solid then it will slowly drift down below 4ma down to zero and then will slowly climb back to a fairly 

accurate reading.   It continually oscillates over a 1-3 min cycle.  Very strange .  My question is has anyone experienced  this problem, and is there a minimum voltage required into the card.

some of the loop power from the sensors are less than 24VDC more like 15

 

Any input is greatly appreciated

 

FPM

[Joe Tauser]

It sounds like your 0V reference is floating between the scale and the input module.  Is the ground from the scale head tied to the ground of the panel?  What type of scale head are you using?

Joe T.

[Ausman]

On 17/08/2017 at 9:32 PM, Fluidpowerman said:

external power supply

Have you tried running everything from the one supply?

cheers, Aus

[Milinda]

I have faced similar problem in  2 projects.can you explain how overcome this issue?

[Ausman]

Milinda, as Fluid did not respond we are all in the dark.

However, Joe's answer is a good place to start.  With a good meter, check all the 0 V terminations amongst themselves over the period of time.

Some other things to do as well.....

Ensure that all control supplies are running from the same phase.

If you run the sensor as standalone and monitor it's output without it being connected to the plc, what happens?

If this doesn't show anything up then please advise type of sensor and circuit layout done.

cheers, Aus