Dear All,

I could like to have the advice from all members of control.com on our plant issue of Rosemount 2051.

The problem is: transmitter still showing the PV value on LCD, but mA output measure from TEST, NEGATIVE terminal showing only 2.5mA. Hart communicator showing "Can not found device." When power 24VDC supply take OFF (purpose to reset transmitter) and checking the power supply is 24.3VDC, then connect power again transmitter not showing PV value, completely black. The electronic board (behind the LCD board) was dead. We change other electronic board, transmitter is normal showing PV on LCD and also mA correspondent.

We found two transmitter same above problem.

Do you have any advice of what is the cause could be highly appreciate.

thanks

 

The 2051 manual says the 4-20mA fail-safe alarm level is equal to or less than 3.75mA

The 2.5mA you report is less than 3.75mA indicating catastrophic failure of the electronics, which is what you found.

Reason?

Could be the absence of the surge or transient protection (option T1) combined with over voltage due to

a) nearby, close lightning strike

b) application of supply voltage > 42.5Vdc or AC voltage at some point or another.

A colleague who worked in the Central America where AC power was always dirty insisted on surge protection on all loop transmitters. He also filtered the DC power output. Some action reduced loop transmitter failures dramatically.

 

David,

Thanks for your reply.

Transmitter electronic board have catastrophic failure I agree. We have setting failure alarm level and Stature level is 3.75/3.85mA i guess.

But this case mA output drop to 2.5mA and Hart communicator can not communicated with transmitter. So I can not found the failure message.
Our transmitter have option T1. But it might not functioning due to no case grounding for transmitter.

Reason a) you give, if it is actually lightning strike, transmitter might damage and can not display the PV value on LCD. But our case, it is still display corrected PV value on LCD, only mA output is not correct so value showing on DCS also not correct.

Reason b) you give, voltage supply > 42.5VDC, is this possible when we output directly from DCS AI module?

AC dirty, might be when welding going on near by. I am not sure.

Is there anybody has same this problem before? Your advice is highly appreciate.

thanks

 

>Our transmitter have option T1. But it might not functioning due to no case grounding for transmitter.

That's right.

Quote from the manual

"The transient protection terminal block does not provide transient protection unless the transmitter case is properly grounded. Use the guidelines to ground the transmitter case. Refer to page 2-29.
Do not run the transient protection ground wire with signal wiring as the ground wire may carry excessive current if a lightning strike occurs."