DIY Current Probe

It's nice he has a sense of humour, even if unintentional.

NT

Reply to
tabbypurr
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Much interesting info here that might be of use:

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Reply to
Cursitor Doom

Well it depends on what meter/scope he has. Some digital meters can work down to microvolts without help.

Reply to
dennis

Cut the track with a scalpel, scrape the coating off, solder an sm resistor across the break and measure the voltage drop. Obviously 1 ohm will give 10mV at 10mA and 10mV may not matter, depending on your circuit. When finished, take off the resistor and solder across the cut.

Messy, but cheap and potentially (!) accurate.

Cheers

Reply to
Syd Rumpo

which is why it won't work. if you have a DIY solution then post it lets see if your theory will actualy work.

why is that the only variable , and how will you take accoiunt of that anyway.

Depending on what and where you want to measure. You have a PC computer board and you want to measuing the current opassing through a particular track on teh PCB. While the computer is on how are you going to achieve this ?

yes I do, enough to tell you're talking crap.

Reply to
whisky-dave

but that doesn't give you non-contact probing.

Make measurements via non-contact probing

and not very practical for those needing this type of instrument.

Of course if anyone has a better method then they can do it can't they.

Then there's those DIYer's that when they can't find the crewdriver a hammer does the same job.

Reply to
whisky-dave

Fuck me, you're right! I hadn't thought of that!

Cheers

Reply to
Syd Rumpo

If you're going to break the track, why bother with soldering in a sense resistor? Might as well just stick an ammeter straight across the bridge!

Reply to
Cursitor Doom

Yes, you could, depending on the circuit. The resistor is maybe easier

- it doesn't matter if the probes drop off or are intermittent.

Cheers

Reply to
Syd Rumpo

It does if you're measuring something time related and you've pretty much d amaged the track too,and then there's shorting things out while trying to m easure others. Of course the tracks are a few mm apart which is quite a lar ge gap on PCBs, there's also a problemm of shorting out other devices.

Reply to
whisky-dave

Christ you're dim.

Cheers

Reply to
Syd Rumpo

ch damaged the track too,and then there's shorting things out while trying to measure others. Of course the tracks are a few mm apart which is quite a large gap on PCBs, there's also a problemm of shorting out other devices.

But now where near as dim as you. How can you say

"it doesn't matter if the probes drop off or are intermittent. "

Reply to
whisky-dave

As compared to using a current meter across a track break, you blithering fool. The circuit will continue to work. Bloody hell.

Cheers

Reply to
Syd Rumpo

Go on then tell us the rest of the variables?

Why are you having trouble understanding any of this? A track is a resistor, you measure the voltage across it just like your digital multi-meters measure the voltage across a shunt resistor to measure current. You sure as hell don't put it through a meter coil like TNP thinks. You can't measure the current with it off BTW so why ask?

You just don't understand it.

Reply to
dennis

Oi dip shit RTFM

The signal from a positional current probe is critically related to its position relative to the conductor.

The size of the conductor (e.g. the width of a PCB track) also has a significant effect.

The measurement result will also include other field effects present at the tip of the probe and not just that coming from the current through the conductor.

But don't worry I'm sure you'll get the result you want without needing to worry about itermittant contacts and shorting out between tracks.

I'm not, you are.

So what is the restance of a track ? They aren't all the same you know.

Reply to
whisky-dave

You are either thick or deliberately trying to wind me up.

Why do you think I said you need a constant current source to calibrate it? Just to ensure you understand.. you connect the constant current source to the track, you measure the current using whatever method you choose like a current probe or the DIY method. You correct for the error it reads. You can then turn the equipment on and do accurate measurements.

End!

Reply to
dennis

Maybe it's you that;s the thick one.

yuo don;t it's inbuit in that unit that's what the calibration is.

you obviously don't get it so give it up, all the information and the use of that device is there for everyone to see, just read it.

Reply to
whisky-dave

I still don't see how this answers the original question. This is a proprietary current probe costing 500 odd quid. A DIY solution was specifically requested.

Reply to
Chris

I do NOT have any idea how to make one of these devices up from scrap compu ter parts any more than I know how to make a DIY Mars or moon rocket. Like others I could come up with crap and spout it or pretend a simple mete r with a couple of probes can do it, but I know better. If someone wants to help the OP then please post all the details rather th an just say it doesn't matter if you have intermittent contacts or short th e tracks out. If you've ever done PCB work you should realise that intermit tent results due to poor contacts are NOT a good way to test anything.

As yet I've seen no solution to the OP problem which was to "sense the curr ent runing through a PCB track", I'd suggest a mind meld with the PCB but unless the OP is vulcan that won't work either. I DO NOT believe the OP wanted to cut up his PCBs or the tracks and put res istors in series with the tracks.

Reply to
whisky-dave

So you actually agree that I was correct! What are you arguing about?

We don't want to use that device, we can't afford £500 is the simple answer you fail to understand.

Reply to
dennis

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