How to measure current in PCB trace?

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Antonyb

Joined: 06 Feb 2009
Posts: 6
Helped: 1
Location: India

07 Nov 2009 10:53 How to measure current in PCB trace?

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).

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LM317

Joined: 07 Nov 2009
Posts: 1
Location: istanbul

07 Nov 2009 12:20 Re: How to measure current in PCB trace?

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

Antonyb

Joined: 06 Feb 2009
Posts: 6
Helped: 1
Location: India

07 Nov 2009 12:30 How to measure current in PCB trace?

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

Joined: 16 Jun 2005
Posts: 152
Helped: 16

07 Nov 2009 12:43 Re: How to measure current in PCB trace?

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

Joined: 07 Mar 2006
Posts: 101
Helped: 14

07 Nov 2009 13:33 Re: How to measure current in PCB trace?

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. (http://web4.lem.com/docs/products/la%20100-p%20e.pdf, this type has a 200kHz bandwidth)

Stefaan

dick_freebird

Joined: 04 Mar 2008
Posts: 307
Helped: 45
Location: USA

07 Nov 2009 20:33 How to measure current in PCB trace?

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

Joined: 24 Dec 2004
Posts: 1833
Helped: 244
Location: New England, USA

08 Nov 2009 7:12 Re: How to measure current in PCB trace?

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

stan4

Joined: 19 Aug 2009
Posts: 10
Location: Nicaragua

08 Nov 2009 7:30 How to measure current in PCB trace?

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

Joined: 22 Jan 2008
Posts: 5151
Helped: 766
Location: Bochum, Germany

08 Nov 2009 10:57 Re: How to measure current in PCB trace?

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

Joined: 06 Feb 2009
Posts: 6
Helped: 1
Location: India

09 Nov 2009 5:03 Re: How to measure current in PCB trace?

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?