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Bench Testing DC Current Transducer

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Hi all,

I am new to instrumentation and want to test out a DC CT (DCT100-42-24-F). I have an ACT CT in my electrical cabinet that is working well, but I cannot get the DC one to work. I have tried 2 different units and both do not seem to be outputting a 4-20 mA output. I was to externally test the DC CT before putting into my cabinet, but I am not sure how to approach it. I am also limited with equipment to do this. I have a basic MM, a basic signal generator, and a variable PS (see below). Any advice is greatly appreciated!


Connect the 24VDC supply to terminal 1 and 2 of the transducer. Use the DMM in mA mode and connect the meter to terminals 3 and 4. You should see the current when there is current flow thru the center of the donut. You simulator simulate a source and thus can't be used for the read out.

Your SHITPWR unit does not appear to have current limiting. That means you'd need a dummy resistor to create a known amount of amps. I suggest a 24 Ohm 50W resistor to get 1A, you'd need the 24V to power the thing anyway.

Then with your DMM you can probe the 4-20mA output.

The amount of passes through the hole determines how many times it should read the known current of 1A.
Eg: 1 pass, 1A should be around 4.16 mA if the thing is 100A full range.

Challenging to get to 100A full range, you'd have to pass the wire thourgh 100 times....

If you have a lab power supply capable of 5 or 10 A it gets easier as you don't need the resistor since you use constant current (CC) mode.

I also have this 24V 6.5A PSU (https://www.meanwell-web.com/en-gb/ac-dc-single-output-enclosed-power-supply-output-hrp--150--24). I am assuming I will not need a resistor if I use this. I also have my jumper removed on my DCT for a 0-50A range. How would I set up to measure the mA output in this case? If I have 24V across terminals 1 and 2, and have the MM leads on 3 and 4 set to DC mA, would this cause a short of any kind or could damage the instrument? 

I have seen on another forum platform of someone using a very similar DCT unit (just a different A range) that said they only had power on terminal 1 and 2 and no load/wire through the core, and they read 4 mA. I am assuming I must have something wrong with my set up or measurement reading if I cant get a similar output?

That's *NOT* how this works.  If the power supply doesn't have an adjustable current limit, you need a load resistor for it to determine the output current.  Unfortunately for a reasonable current of a couple of amps from a 24V PSU this will be a very high power resistor, which wont be cheap, and if metal cased, will also need a good heatsink.

Most of us would test this sort of thing on a 0-30V, 0-3A or 0-5A CV/CC Lab Bench PSU, in CC mode with a multimeter on 10A range in series with its output, and however many turns of wire through the DC CT core hole it takes to get the desired effective maximum current as Jeroen already described.  A 5A bench PSU could reach 100 effective amps with only 20 turns of wire through the hole. 

Its designed for use in a 4-20mA signalling loop - 4mA would be zero current through it and 20mA full scale current.    As BeBuLamar has told you, when supplied with 24V power on terminals 1 & 2, a multimeter connected between 2 & 3 3 & 4 on a 200mA range should read 4mA with no wire (i.e no current) through the CT core hole.  If you can manage to pass 50A DC through the hole, and you have removed the range setting jumper to select 50A (low) range, it should read 20mA.  If it stays at 4mA the current flowing through the core hole is probably in the wrong direction.

Edit: corrected output terminals


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