BigSteve

0-10V output drops when connected to Micrologix 1400

10 posts in this topic

I am a PLC newbie, so forgive me if there is a simple solution; I have a new Omega 0-10V differential pressure transmitter that I am trying to use for level detection on my Micrologix 1400 (replacing a conductivity level probe that is not accurate enough).  When I have the output wire disconnected from the PLC (ie: transmitter is receiving the 0 and 10V input, voltmeter is connected to the 0V and output line out of the transmitter), I see the voltage output I expect, and when I drive 10V to the PLC through the output wire at the instrument and the 0V wire, I get the raw value I expect in micrologix, but when I connect the output from the transmitter to the PLC, the voltage drops to 0.98V (I see the corresponding raw value in micrologix) and I get no response from the transmitter - it stays at 0.98V no matter what the level is.  The I/O is configured for -10/+10V, not 4-20mA.  Does anyone have an idea of what is going on?

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Can you share how you're wiring the loop?

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well that is a bit convoluted description. it would be easier to follow with actual models of both devices, used circuit, and marked terminal numbers for easy reference.it could be defective transmitter, wrong wiring, wrong configuration etc.

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Okay - when I disconnect the instrument, and drive 10V across -Excitation and +Output, I see full range in Micrologix.

When I connect the +Excitation and -Excitation to the PLC cabinet supply voltage (+Output is disconnected from the PLC), and connect my voltmeter to the +Output of the instrument and -Excitation, I read variable voltage based on the tank level (it is transmitting the signal correctly).

When I connect the instrument to the PLC as drawn, I get a raw value in Micrologix of 2867, and 0.98V (per my voltmeter) between the +Output and -Excitation wires, and the output does not change with the tank level.

instrument wiring.jpg

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Can you provide the complete catalog number of your Omega transmitter. And the Analog card.

10volts to power a transmitter is very unusual.

 

And where is the 10 volts coming from on the PLC side?

Edited by Mickey

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1 hour ago, Mickey said:

Double check input selection dip switch, default is current. See PDF

dipswitch.pdf

That did it.  Thank you!

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3 hours ago, BigSteve said:

That did it.  Thank you!

You're welcome

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Once Again RTFM is the solution of choice! LOL.

Welcome to the forum Big Steve and thanks for hleping him Mickey.

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