Would anyone know the specification for the 4-20ma transmitters (Mark V loop powered)used in the controls of a GE 7EA turbine (yr 1998 vintage).

We tried connecting a Foxboro 24vdc 4-20ma Model IDP10-D20A01C-L1B2C1K1 pressure transmitter to the Mark V analog card and the input point resistor failed. Everything looks correct around the card termination terminals and field wiring. Wondering if there are special spec's for these transmitters.

 

Is the transmitter two-wire, three-wire or four-wire?

Specifically, which input terminals and terminal board are you trying to connect the transmitter to?

If the transmitter is "smart", it probably won't work with the Mark V.

The "24 VDC" output of the Mark V is more like "21 VDC", and while most transmitters work fine with that, some don't on the Mark V (I believe it's because the Mark V input dropping resistors aren't always 250 ohms).

If you can provide more details about the transmitter, what you're using it to measure, and where, specifically, you're connecting it to the Mark V (terminal board, core (processor the terminal board is mounted on), and terminals) we might be able to help you.

The Signal Flow Diagrams in Appendix D of the Mark V Application Manual, GEH-6195, have the details of the terminals, dropping resistors, and any ground reference resistors. Some--not all--of the analog inputs to the Mark V have ground reference resistors which can be used to reference the input circuit to ground, <i>if the loop isn't grounded at the transmitter or somewhere else.</i>

 

Thanks for the information CSA

The transmitter is 2 wire configurable for digital or 4-20 ma.
We connected it to R core card, analog input 4-20 ma card #DS200TBQCG1AAA point MAI05 terminals 047 and 049 BJC5 jumper is in

R5 resistor overheated with in a few minutes.

We did/do not ground the + or - wires, only the shield and at the Mark V end only.

I will try to find the info you refer to.

 

Hi CSA,

We found that the Foxboro IDP10-D transmitter was connected reverse polarity. According to the supplier of the Foxboro transmitter, it does not protect the external circuit from reverse polarity (can draw up to 1 amp or more), it only protects itself. Does the 4-20ma input card DS200TBQCG1 not have any current limiting on the analog input loops?

As the GT was originally supplied with Gulton Statham transmitters, would you know if they protect the external circuit against reverse polarity. I would think that a simple diode in the front end of the transmitter circuit would protect both the transmitter and the external circuit against reverse polarity, would that be correct?

Thank you
LGT

 

Interesting, I read the original post and for the life of me I couldn't think of how one would burn up an A/I input resistor because I mentally assumed correct polarity. But a power supply's voltage across a diode and a 1/4 watt input resistor? I can smell the smoke. I should know better by now.

I don't think an instrument manufacturer has any obligation to protect external circuits against installation with the wrong polarity. Maybe it makes a case for a low wattage input resistor for fusing.

I was amazed when I discovered about 3 years ago that a flowmeter's 4-20mA output was NOT reverse polarity protected and was instantly destroyed by the power supply's reverse polarity connection. I had thought that all 21st century instruments from major manufacturers would have been protected against reverse polarity hook-up.

On the polarity topic, interestingly enough, the Honeywell sales guy came around recently, stating that their newest pressure transmitter could be hooked up in either polarity and it would work.

When I connected a HART modem across the resistor that they'd installed in the loop circuit on the demo he brought along, I couldn't get a connection in Pactware (as it turns out, it was a licensing issue, nothing to do with the loop circuit).

To make sure that the xmtr was truly pumping current, I put a milliameter across the test terminals and got a negative current reading, even though the meter's polarity matched the polarity of the meter's lead hook-up. I'm scratching my head, even checking to make sure the red lead was in the meter's positive jack and the black lead in the negative jack. I was stumped how a milliameter could possibly read backwards. Huh ? ?

The meter wasn't reading backwards, it was reading exactly what it saw - the polarity was flipped with respect to the (+) and (-) test terminals ! ! ! The demo's power supply, a 24Vdc wall wart, was wired reverse polarity, but sure enough, the transmitter was functional, display was fully functional, with the loop current amplitude being what it should be.

Had the current signal been wired across an analog input, the AI would have been driven off scale down scale, but hey, the transmitter works wired backwards . . .