Fieldpoint Noise

[ssk]

I am witnessing a strange situation on my Fieldpoint system.

I have one FP1000 and two RTD-122 modules (both fully populated). The RTDs monitor the temperature in 4 mixing tanks.


The Fieldpoint modules are housed in a separate metal, (earthed) enclosure along with a DC power supply. All of the RTD cables are shielded and connected to earth at one end.

The main control panel houses three inverter drives (all with manufacturers input filters fitted), and some other control gear. Motor cables are all screened and screen are terminated correctly.

The system has been running perfectly for several months, until last week. I had a call to go to site because the temperature reading were 'all over the place'.

Whenever any of the three mixer motors are now run, the temperature readings float from -50 to +200. Stopping the motor returns the temperatures to their normal level.

The only event that has occured recently is that some sub-contractors dropped something on the armoured supply cable (which is outside), and fractured the insulation on the case of the cable and some of the conductor insulation. Due to heavy rain, water has leaked into the cable and it has eventually tripped out the supply. Is it possible that this may have damaged the filters?

Anybody experienced similar problems with Fieldpoint?

Thanks in advance

ssk

[Wayne.C]

ssk,

Company I work for sells drives and most of the problems I've seen like this are caused by bad grounding.  In your case it worked and then quit after damage to cable.  I suspect that the ground wire in the armored cable may have been damaged.  Has the damaged cable been replaced? Input filters on power supply will not work without a proper ground connection.  Suggest you install a new supply cable.

If the cable has been replaced, double check that the input supply ground to the power supply has been properly installed.  Make sure that no changes were made in how wires were routed and how they were connected.  If all supply connections have been double checked and found to be correct, then I would replace supply.

[ssk]

Thanks for the comments. The cable has been repaired with a junction box (the damaged section has been chopped out).

Maybe it is damaged elsewhere, I will investigate.

ssk

[B._Beeman]

I agree that it sounds as if your shield has been compromised. A good place to look would be at how the repair was done at the damaged section. Often folks will "connect" a shield via a drain wire through a pin in the connector. This is not sufficient in high noise enivironments as the drain wire/pin is a high Z at high frequency. Another thing to watch for is the new connectors causing your shield to now be tied to earth (or some other undesired path) at the connectors not at the single point you originally had. The repair is trying to replicate the original shielding of the cable at that point, which means fully enclosed in metal which is insulated from any thing else - not always easy to achieve at connectors.....

[feild point]

I am also facing similar kind of noise issue which is suddenly started. My RTD cable also sheilded and earthed to a signal earth which is totally isolated from power earth. The problem starts whenever the drive(VFD) switch on and is normal when drive powered off. The power earth to VFD is also OK.  Now I reduced number of RTD channels  connected and noise came down. If I add any additional channel I can observe the noise . Can any body help to rectify the issue

[ssk]

My problem was  a result of the vfd's input filter being damaged. A quick way to prove if the vfd is the source of the porblem is to reduce the carrier frequency, if the noise gets less then it is probably due to some problme with the vfd/earthing.