Current transducer

[Priyadarshan]

Dear Friends
I have a problem with a current transducer which measures the current to a grasso screw compressor.
The transducer make is schneider, input 0-5A(supplied from a CT), output 4-20mA, power source 230V AC 50/60Hz.
The problem is that when the compressor is in standby, due to some fluctuations in the supply the current signal drops below 4mA and this cause alarm in the PLC (GSC system which comes along with compressor). How can I filter the supply? or is there any other remedy for this?
Please help me..

[NoNickName]

Why don't you install a cheap computer UPS between the mains and the current transducer?

[EDDC]

actual operation of the transducer is low voltage dc. adapt the transformer / switching rectifier setup to charge a small gel cell in parallel feeding the electronics. of course a 230v ups would be much easier if you can find it.

eddc

[Electrocoolman]

Can you post the model of the schneider transducer. They are normally good with their literature.

When compressor is in standby, that should result in zero amps flowing, which should be equal to 4mA.

It sounds as if the system needs calibration, or have you noise on the system?

[Peter_1]

Electrocoolman, I think the same, you can buy cheap RC's to filter out some noise.
What's the pressure range of your transducer, if its 0-.... then it only can give lower than 4 mA if lines break.
You could also re-program the PLC (I think it's a Siemens S5 or S7 for Grasso) so that there must be a certain time lapse below 4 mA before this is a real alarm. You then filter out the nosie with the PLC. Just an idea;
You're sure it's not the transducer itself giving you troubles?

[Priyadarshan]

The PLC is siemens C7.But I dont have the source of the program used in the PLC, and I dont think I will get it from grasso.

Anyway on further testing I found out that these fluctuations are coming from a siemens micromaster VFD which is running on the same panel.

After that I put a 10microFarad capacitor parallel to the current signal to the PLC. Now it is filtering the signal. And the system is working fine.

But I am not sure whether this will cause any other issues later.

[Electrocoolman]

Good news that you've cured it.