in-rush current measurement.

How would I go about measuring the in-rush current on a DC feed of 30V. I have built a current limiting circuit which should limit current to 8mA and I need to how that the in-rush current does not exceed 10mA for 100ms.

Currently I use a relay to switch the feed on and off, however this bounces so I am going to replace this with a mercury wetted 0 bounce relay is this the correct thing to do?

Most sites I have seen discussing in-rush current seem to use a current probe but they are measuring Amps if not 100s of amps on motor feeds not a few milli amps are there current probes which can measure the mA range accurately enough for me.

Currenly I am using a shunt resistor in lieu of the current probe and notice that I appear to exceed the in-rush just from powering the current limiter without a load although only for the firt 12uS. Is this likely to be noise from the relay or the response of the transistors limiting the current, I am using a Transistor VBE referenced current source circuit from AOE, is there anything I can do to remove this initial spike or do I need to allow that there will always be this inital rush.

Any good web sites with this sort of info would also be appreciated

Many Thanks for any help


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Maybe, maybe not. The bouncing should not of itself cause problems.

Might adding a smallish inductor to the power line work?

Alternatively, a small resistor, in series with a capacitor may work, if you can connect it to the supply permenantly. The capacitor supplies the load when your supply is connected.

A small capacitor on the base, with a time constant of a few microseconds may also work.

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Ian Stirling

a good solution for wireless measurement is

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I think "mires" is a robot that randomly follows up threads with an ad for these makers of defective equipment.

--   forging knowledge
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Ken Smith

Your SPAM is not appreciated here, and you can rest assured I will
never buy anything you have to offer because of it.
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John Fields

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