100 mA(AC) Current Sensing devices

[josedavidch]

Hi

I have been exploring many many sites looking for a low current sensing device capable to send 50mA to 500mA AC currents.

I have tried some from

http://www.crmagnetics.com

but those are very suceptible to noise, and my circuit, having 20 lines carrying 100mA produces such level of noise that sensor where lines are OFF, sense current due to induced noise to the sensor.

Does anyone have a tip on devices for this job?
- Sensor should sense current by induction
- Sensor should have relay or NPN output

Please someone advice.

 

[ScottyUK]

Current monitoring relays are available from most of the major manufacturers. Here's one for a free start - after that hit the catalogues!

http://ecatalog.squared.com/catalog/173/html/sections/21/17321028.html#1014305

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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

You aren't getting a lot of help because your question has not been clearly stated. I don't know what you're asking...

NO CLUE.

I think you may have spelled some words wrong and haven't noticed.

Restate or correct your question and we'll be happy to help.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Tell us a little more about your application. The problem may be in your circuit rather than with the relays. CT based relays such as you are using typically have good immunity to currents external to the sensing loop.
respectfully

 

[logbook]

> ... looking for a low current sensing device capable to send 50mA to 500mA AC currents.

We assume you actually mean :
> ... looking for a low current sensing device capable OF SENSING 50mA to 500mA AC currents.

... since you mention 100mA currents to be sensed.

 

[josedavidch]

Yes.... the word is sense.

Thanks for the clarification.

 

[danw2]

It sounds like you're using a sensing relay, a CT with circuitry to trip a relay. My experience with CR magnetics AC current sensing relays has been favorable. They use a toroid type CT to sense the current that I've found to be relatively immune to external industrial EMF.

What about the various sources for noise? power supply, common connections on the input device (PLC?), or the current sense CT itself? Can you isolate the current sense CT and see what happens?

 

[josedavidch]

We use CR devices for other industrial applications on motors and other heavy duty.

This particular application is called "conditioning" in where you apply 1500VAC to the a spark gap (gas filled) and once ingnited, allow 100mA flow for more than 10 secons. The application do this to 20 spark gap (SG) at time.

We have made the following test:

1- Load the conditioning nest with only 1 SG. Under this scenerio, the line in which the current is flowing, affects some sensors on the vicinity.

2- Same test as #1 but unplugging any connections to PLC. The same happens

3- Load only 19 positions with SG. Under this scenario, the empty position will trip the sensing relay as if a SG were there.

4- Same test as #2 but unplugging any connections to PLC. The same happens

5- Using faraday gage to all devices. It reduces the noise acceptance but not to the level we need.

6- Under scenario #5, we eliminate all the cables thru 19 of the sensors and only allow one of them to sense current. Under this scenerio, some of the sensors (near by the one where current is flowing) just trips the relay.


We have some other machines like this where the current is 1A or 5A. Using other kind of current sensors we don't see this kind of problem, cause there is a good difference between 100mA and 1-or-5A.