Ab plc 5/15 analog problem hooking up hart 475

WE have a ab 5/15 on a compressor when one of the techs hooked a hart475 to a discharge pressure tramsmitter , the compressor shut down on surge , it will only shut down if the surge limit is hit 3 times in a hour . So I log on to PLC and put a trend on the surge alarm as soon as he with on line with the transmitter the analog start spikeing up and down hitting the surge alarm, I check 3 more transmitter on this compressor and they all would screw with the analog every transmitter , each transmitter i tested was on diffent cards. And I two 475 same with both.
Has anyone ran in to this problem with AB 5/15 and hart 475

thanks
Billy

The 475 can optionally talk Foundation fieldbus (FF), as well as HART.

Is your 475 equipped with FF? I could imagine that a device attempting to talk FF on a HART line could well introduce a lot of noise.

I heard something similar not long ago they used a 250 ohm resistor in series this helps when some times when the communicator don't recognize the device.

Had the same problem on 2 of our compressor . Both on 5/15 plc . When the tech hookup to a pressure transmitter with 475. What happen to us ,He was checking transmitter for problem and it was running on the border line of tripping on high pressure when the hook to the transmitter and with online the pressure with up and trip the compressor and shut down the unit. I was call to check on what happen been the unit was down I when on line with the plc and watch the pressure loop on the transmitter and every time he when on line with the 475 the pressure would go up a couple PSI. So we try this on 3 other AB 5/15 and same thing, Try it on AB 5/40 did not have that problem . I think it is a Problem just with the AB Classic PLC 5.
we put in other transmitter so both would have to go high before trip ,so tech could connect to 1 and be ok.

LOL I answer my our question LOL