# Non invasive Method to measure if there is any current in a line

We have a project where we have to measure if there is any current through the a cable, but having not common ground and knowing that the current could come direct or reverse direction. We thought about the chance of set a differential opamp, but if the current came reverse that would be a problem . We also thought about optocupler but we cannot limit the current so much.

Any idea is welcome,

Carlos

• If you're able to put a sense resistor in the line like you drew, just check any of the analog chip vendors for their current-sense amplifier offerings. Most are not bidirectional, but a few are. Mar 24, 2017 at 16:28
• How much current? AC/DC? What is the line voltage? Mar 24, 2017 at 16:34
• You can consider using the ACS711 or similar. These are based on Hall effect rather than voltage drop in a sense resistor. Check it out and see if it meets your needs. Mar 24, 2017 at 16:37
• If you need to measure the current vs. just detect if there is any you can buy off-the-shelf non-contact AC and DC current sensors where you run the conductor through an aperture. I have used modules from LEM, they're very high quality and they have a wide range of products: lem.com They may be overkill for a current/no current sensor. Mar 24, 2017 at 16:43

A hall effect sensor can be used for what you appear to want. It produces a signal in the presense of a magnetic field and any current passing through a conductor produces a magnetic field: -

A saturable reactor is also something that can be used to detect the presense of current in a wire providing the wire carrying the current is wound close to the core of the saturable reactor.

• Is this the same principle that they use in contactless multimeter? (which has a hook-like probe) Mar 24, 2017 at 16:34
• @ammar.cma some might use this method but generally I guess a CT is used for AC current measurements. Mar 24, 2017 at 16:35
• seems like my only way is hall effect...but i got another problem, the current i measuring is in the milliamps order, so maybe...not suitable ? :( Mar 29, 2017 at 18:54
• Form a ten turn loop if you can and this multiplies the field and makes it easier to detect or measure. Mar 29, 2017 at 19:58

Quite a few ways.

1. Hall effect sensors.

2. Current transformers if it is a.c.. It can be as simple as a few windings over the wire.

3. Thermal effect, like those used in airflow meter.

4. Compass or magnetometer.

5. Run the wire through a magnetic field and attach a needle to it. Essentsilly making a galvanic ammeter out of it.

..... I'm sure you can think of more.