recording elecrical current?

Question

I have a yokogawa recorder 436004 and need to know if and how I can record 5-20amps. recorder is designed to record Millivolts, t/c, or rtd inputs.

Answer 1

There are several ways. The best way but probably not the easiest is to sense the conductor's magnetic field with a Hall effect sensor.

The easiest way would be to measure the voltage drop across a length of conductor. It would help if I knew how many millivolts is full-scale on the recorder. I will assume 100 millivolts full-scale.

100mV / 20 A = R = 5 milliohms

Choose a big enough wire so it does not heat up with current, because heat causes resistance change. 10 gauge wire has about 1 ohm per 1000 feet, so 5 feet = 5 milliohms. 12 gauge wire has 1.59 ohms per 1000 feet, so 3.1 feet = 5 milliohms. I don't think you want to use much smaller wire than that because of the heating issue.

Answer 2

You need to buy a Kelvin Shunt resistor. The current passes through the small valued resistor and produces some number of millivolts per Amp of current (it will be listed on the device) according to Ohms law. The resistor value will be less than 1 Ohm, but very accurate and temperature compensated.

Or you can get some 0.1 Ohm power resistors (like 10W, 25W) and use them. Just measure the value of the resistor accurately (i.e. 0.098532 Ohms), and pass the current through the resistor, while recording the voltage across it.

The only caveat to this: Make sure that the common mode voltage does not exceed the recorder's capability. In other words, make sure that one side of the Kelvin resistor is near ground potential. Don't measure "high side" current or you'll blow out your recorder channel.

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Answer 3

wrap a few turns of insulated wire around one of the wires running to your load.

calibrate by using a known load, so that you can convert the voltages recorded by your yoko into amperes of current.

note this will not work for DC circuits.

TLBS's answer would work for DC or AC.