Hardware damping filter for current signal

[mikas_m]

Hello to all,

I need some kind of hardware filter with possibility to adjust damping from let say 1 to 5 sec. I need this to try to smooth mA signal that is noisy. I'm not able to implement this filter in software of PLC (software locked). What would be good is to have some kind of galvanic isolation circuit with this possibility.
Can you suggest something?

Thank you

 

[Peter Nachtwey]

I would trying to reduce the noise first. A RC filter with a 0.2 to 1 second time constant would filter your input as suggested. A one microfarad capacitor and a 1 megohm resistor would have a time constant of 1 second. A 200k Ohm resistor would have reduce the time constant to 0.2 seconds. It takes 5 time constants for the signal to reach with 1% of the final value.

You should be able to make a low pass filter in the PLC easily if the desired time constant is that long.

 

[mikas_m]

Thank you for the reply.

is there some kind of standard robust industrial solution?
I wouldn't want to build it myself.
I have no way to make filter in PLC.

Thanks again

 

[Peter Nachtwey]

Oops, I forgot you are using 4-20ma

My idea with the RC circuit would only work with a high impedance voltage input. 4-20ma inputs usually have a 250 input resistance so putting a high impedance in series won't work. You would need a very big capacitor across the input to filter a 4-20 ma circuit.

I would concentrate on making in the digital filter in the PLC. It isn't hard.
Do a search for low pass filter on this forum.

 

[Mickey]

See links below

http://www.kemo.com/kemohtml/basic_p_420filters.htm

http://www.google.com/#hl=en&sclien....,cf.osb&fp=af73696fe4de10c7&biw=1585&bih=807

 

[Banker]

Hi

It is very hard to make a filter in the PLC if the software is locked.;-)
Try to google PR electronic this company make what you want.

Banker