I like to detect current passing through a wire. I have only a very small opening (15-20mm diameter) that access to wire so using a current transformer is not feasible. I can touch the bare wire. (I can touch with a tip of a scope probe) The wire carries 1 - 10A and 220V. I am looking for a non-contact or contact way of understanding the current passing through. 10% accuracy is good enough.

Any pointers?

  • \$\begingroup\$ If you can reach the wire you can use a clamp, but seems that the hole is very narrow \$\endgroup\$ – clabacchio Feb 17 '12 at 9:30
  • \$\begingroup\$ Indeed. The hole is narrow. I can measure the voltage nicely but don't know how to find out current. \$\endgroup\$ – Ktc Feb 17 '12 at 10:23

A Hall cell insulated and pressed against the current carrying conductor will allow current to be monitored.

You will get a few zillion ideas from these images - each is hot linked to a page.

There are MANY hall sensors available which would do this job.
The items below are far from the cheapest but are better optimized for this task than many due to integrated "magnetic concentrators".

Digikey will happily sell you the devices below

enter image description here

Good article here

These novel, contactless current sensors consist of an integrated CMOS Hall effect sensor covered by an additional thin, ferromagnetic layer on its surface. This IMC layer acts as a magnetic flux concentrator, providing a high magnetic gain that increases the sensor's signal-to-noise ratio. The sensor is particularly appropriate for DC and AC current measurement. Such measurements are characterized by the need for ohmic isolation, very low insertion loss, fast response, small package size, and low assembly costs. Typically, current sensors are found in applications such as battery current monitoring, solar power inverters, and power inverters that drive traction motors in EVs (electric vehicles), and HEVs (hybrid electric vehicles). There is no upper limit to the level of measurable current of IMC sensors, since their output level depends only on the conductor's size and its distance from the sensor.

Available here

Datasheet here for one version - SOIC8.

  • \$\begingroup\$ I have a question regarding this approach. According to the this tiny.cc/upana I better use a magnetic element around the cable to amplify the signal. Based on experience, is this really necessary? \$\endgroup\$ – Ktc Feb 22 '12 at 1:40
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    \$\begingroup\$ @Ktc - its an option. Adds sensitivity if you can achieve it in the space available. Note that the IC that I gave as an example has flux concentrators built in on a flat surface. \$\endgroup\$ – Russell McMahon Feb 22 '12 at 10:34

Many current transformers have smaller openings than 20mm. That's actually quite large. A Hall sensor will work anyway as Russell has described, but don't dismiss a current transformer due to a misconception of what they can do.

One important difference between a Hall sensor and a transformer is that the Hall sensor works down to DC. If you are measuring AC current only, then that doesn't matter.

  • \$\begingroup\$ Don't I need to wrap the CT around the cable? I am not so sure this is possible or feasible? \$\endgroup\$ – Ktc Feb 22 '12 at 1:41
  • \$\begingroup\$ @Ktc: Current transformers are usually rigid devices, so you can't wrap them around anything. Some current sense transformers come with a hole that you feed the wire thru you want to sense the current in. As I said, 20mm is actually quite large for such a hole. You can also loop the wire thru the hole several times for increased sensitivity. The output is proportional to the total current flowing thru the hole, whether that comes from multiple segments of wire or not. \$\endgroup\$ – Olin Lathrop Feb 22 '12 at 14:03
  • \$\begingroup\$ I see. In this case, wire is accessed through this 20mm hole but I cannot disconnect the wire and put it through the cable. This needs to work out without me doing any disconnect of the wire. \$\endgroup\$ – Ktc Feb 22 '12 at 16:01

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