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How to measure current in PCB trace?

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Antonyb

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Hi,

What method is best to use for measuring the current flowing through a path in a PCB. Will it be better to use a current sense resistor or a current transformer?
I need to sense a pulse current whcih will be ON only for short duration (Of the order of usec).
 

LM317

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you should use a sense resistor and measure voltage on it by using oscilloscope..
 

Antonyb

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But the current which I am expecting to be flowing is of 100A (Remember pulsed). Moreover the applied voltage will be of 300V. Will a CSR be a good way of measuring the current?
 

hakeen

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Hi

For best linearity, resistor would be a better choice. In transformer, you will have more serious non-linearity problems.

Your range of current (100A) is still OK for many resistors. Just try to use as small as possible value to lower overall consumption.

Cheers
 

svhb

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It depends also on how short the pulses are. Be sure to select a low inductance type sense resistor.

If the frequency is moderate, you can consider a LEM current transducer. This has the advantage of an isolated measurement from the high voltage. (https://web4.lem.com/docs/products/la 100-p e.pdf, this type has a 200kHz bandwidth)

Stefaan
 

dick_freebird

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If you have a known good spec, or better yet a 4-point
(Kelvin) measurement of the trace without power applied,
for trace resistance per length then you can use that and a
simple voltage difference reading to get your current
without having to cut and add a sense element. Though
PCB traces are meant to be pretty low resistance, so if you
are looking at low currents that would test the sensitivity
of your voltmeter perhaps. Not in this case.

I have seen current transformers that have that high a
saturation current, advertised. That needs a cut and a loop
of wire.

You could float your 'scope with an isolation transformer
so that the "ground" potential comes from the 'scope
probe, and see the pulse using the trace resistance as your sense.

100A is a mighty high current for a PCB trace.
 

biff44

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With 100A, there will be some serious magnetic field in the area of the conductor. Try a hall effect sensor.
 

stan4

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CSR would probably be your best choice.

PS: I'm curious, I can't figure out what kind of application requires useconds pulses of 100 amps and also to measure it.
 

FvM

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Seriously, the question for best method can't be answered without a full specification. An AC only measurement generally
suggests a current transformer or di/dt sensing (Rogowski) coil. Both provide high bandwidth, isolation and low interference
susceptibility, the latter also insensitiveness to DC currents and effectively unlimited overload capability.

But the particular specification may be a reason to prefer other methods.
 

Antonyb

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Hi,
Am planning for a current measurement ways now, since the PCB is not yet fabricated I will not be cutting the track and all. Am looking for which method would be the best one to measure the current.
As all of you have stated, the CSR would be the best method for liner measurements. But can you also suggest few Hall effect sensors for PCB mount?
 

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