flex IE8 raw issue

merlin00724

Member
Join Date
Oct 2007
Location
cincy, OH
Posts
45
I am having some issues with a 1794-IE8 flex module on a controllogix plc. this is measuring the weight of a tank on load cells. the scaling seems to be right with the module set for 4-20mA and the raw min/max is 0-30840, but with a measured 3.8mA from the transmitter I am getting a raw value of 40. which is showing the tank as not empty when it really is. we have about 12 tanks set up like this and they all behave the same, and have since being commissioned new. so I am not really going down the road of thinking I have an isolated hardware issue. if I simulate 3.7mA to the module then I finally get a 0 raw value.

any advice on how to tighten this up so that at 4 or 3.9mA I can get a 0 raw?
 
That is 0.1 of 1 %, pretty small error. What is the engineering units (span)?

Can the 4-20ma transmitter be adjusted(calibrated)? If not you could do this in the PLC.

If it is just a high zero issue you could program a zero cut-off. Any thing below value xxx will show zero. Common method as most transmitters drift a little.
 

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