Sensing really low currents

Thread Starter

HighVoltage!

Joined Apr 28, 2014
142
Hi all!
I want to "sense" really low currents in a 3 Phase system (Currents as low as 2-10mA). I want to be able to also monitor using a data logger. Not sure how to go about this?:confused:
 

Hymie

Joined Mar 30, 2018
860
Not something that is easy to do, depending on how much you want to spend you could considered buying three of these, dismantling them to find an internal voltage proportional to the measured current and feed that to your logger (x3).

https://www.ebay.co.uk/itm/ACM91-1mA-AC-DC-Current-Digital-Clamp-Meter-True-RMS-Meter-Low-Impedance-Tester/273798225461?_trkparms=aid=111001&algo=REC.SEED&ao=1&asc=20131017132637&meid=5ee0558041584cb094830ac8085cd663&pid=100033&rk=3&rkt=8&sd=223215672863&itm=273798225461&pmt=1&noa=1&pg=2045573&_trksid=p2045573.c100033.m2042

Of course, buy one first to investigate its performance and that you can locate a pick-off voltage to feed into your logger, which might not be easy on surface mount components.
But for under £105 you could have the front end of your 3 phase current monitoring system with a resolution down to 1mA (which I reckon would be hard to beat).
 

wayneh

Joined Sep 9, 2010
16,399
Hi all!
I want to "sense" really low currents in a 3 Phase system (Currents as low as 2-10mA). I want to be able to also monitor using a data logger. Not sure how to go about this?:confused:
Just an out-of-the-box thought. The range you cited happens to be the working range of a typical LED. If you have the voltage to light an LED, you could just use LED brightness as your current sense. Probably not what you’re looking for, just a thought.
 

Thread Starter

HighVoltage!

Joined Apr 28, 2014
142
Not something that is easy to do, depending on how much you want to spend you could considered buying three of these, dismantling them to find an internal voltage proportional to the measured current and feed that to your logger (x3).

https://www.ebay.co.uk/itm/ACM91-1mA-AC-DC-Current-Digital-Clamp-Meter-True-RMS-Meter-Low-Impedance-Tester/273798225461?_trkparms=aid=111001&algo=REC.SEED&ao=1&asc=20131017132637&meid=5ee0558041584cb094830ac8085cd663&pid=100033&rk=3&rkt=8&sd=223215672863&itm=273798225461&pmt=1&noa=1&pg=2045573&_trksid=p2045573.c100033.m2042

Of course, buy one first to investigate its performance and that you can locate a pick-off voltage to feed into your logger, which might not be easy on surface mount components.
But for under £105 you could have the front end of your 3 phase current monitoring system with a resolution down to 1mA (which I reckon would be hard to beat).
Do they have current transducers this low?
 

Hymie

Joined Mar 30, 2018
860
The current clamp can measure low level currents (both AC & DC), to do this there will be some active sensing device, the signal from which will be amplified to the meter section of the clamp-meter.

So the current clamp will not consist of a simple coil wrapped around the conductor, that is why you will need to locate a voltage within the clamp-meter which it is using to display the current value (as stated this may not be easy to locate, pick off and connect to your logger circuit).
If you are not experienced in electronics, the above will almost certainly be beyond your capabilities.
 

crutschow

Joined Mar 14, 2008
25,423
A proper sized current transformer (three needed) should be able to sense that current.
You can wrap more turns of the AC power through the transformer core to increase its sensitivity (proportional to the number of turns).
What is the the maximum current of the system?
 

Thread Starter

HighVoltage!

Joined Apr 28, 2014
142
A proper sized current transformer (three needed) should be able to sense that current.
You can wrap more turns of the AC power through the transformer core to increase its sensitivity (proportional to the number of turns).
What is the the maximum current of the system?
Approximately 10mA. What CT could I use? Model?
 

Hymie

Joined Mar 30, 2018
860
When I first got into electronics, current clamps could only measure AC currents; I’m not sure when someone worked out how to use them to measure DC currents, but it was a good few years ago.

Earth leakage current clamp meters (measuring down to less than 1mA) have only been around for less than 10 years. It is not a simple matter of using a low current transformer due to only one turn being clamped, plus pick-up noise at mains voltage.

If it was an easy thing to do (measure down to less than a mA), it would have been done years ago.
 

Janis59

Joined Aug 21, 2017
1,224
10 mA.... Actually really small currents are 3 femtoamperes full scale, thus the best ever made OpAmps today may sense the SINGLE ELECTRON flowing along the wire. Would not spoke about if not used personally.
10 mA is drastically large current capable even to slaughter the man.
 
Top