Possibly a newbie mistake involving x10 probes

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brettc
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Possibly a newbie mistake involving x10 probes

Post by brettc »

Hi all,

I think I'm making a bit of a dumb mistake here... using a 2204A with x10 probes and attempting to measure <24v signals. I've got the switches on both probes set to x10, and under the menu for each probe (clicking the A and B buttons) I've got the probes set to x10, and yet it still shows overrange on both channels when measuring anything over 20v. The voltage measured is correctly scaled (5v = 5v displayed).

I was under the impression that the x10 probe attenuated the physical signal so 24v = 2.4v going into the scope, meaning it shouldn't trigger as overrange as the input stage of the scope can handle the smaller voltage, and then it's scaled back up to the correct voltage in the software... but if this is the case, it should be able to handle up to 200v without going into overrange, which is not happening.

Am I doing something wrong? Or is my understanding of x10 probes wrong?

Thanks, Brett

bennog
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Re: Possibly a newbie mistake involving x10 probes

Post by bennog »

Your understanding of 1:10 probes is ok.

But measuring mains voltage with 1:10 probes is not done, and can be lethal.

You are probably seeing overvoltage because of some spikes that go over 200V on the input of the scope.
Try setting the scope to 1:1 and the probe to 1:10 and measure the 5V again you should measure 0.5V if so then the probes are ok.

Try then measuring a 24V power supply (bench psu) or something.

Benno

brettc
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Re: Possibly a newbie mistake involving x10 probes

Post by brettc »

Hi Benno,

If I switch the probe back to x1 and measure with the software configured to x10, 1vDC measures as 10v... going the other way, if I have the probe at x10 but set the software to x1, 10vDC measures as 1v, both as I would expect. With both the software and probe set to x10, the voltage reading is accurate. So I can't fault the measuring correctness, only that it won't display voltages over 20v.

And yeah I'm aware of high voltages (while I'm still learning with picoscopes, I've been in electronics for a long time). I'm not trying to measure 200v, only 24v.

bennog
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Re: Possibly a newbie mistake involving x10 probes

Post by bennog »

24V should be no problem with a 1:10 probe.
Probably some short spikes from cel phone or other emc related stuff.

You do use the ground clip of the probe ?

Benno

brettc
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Re: Possibly a newbie mistake involving x10 probes

Post by brettc »

No, it's not spikes. I can bring the power supply up and the moment that it hits 20v it goes into overload. And yeah I'm using an earth clip.

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Re: Possibly a newbie mistake involving x10 probes

Post by Martyn »

Which software are you using? and have you set the range to Auto?
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brettc
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Re: Possibly a newbie mistake involving x10 probes

Post by brettc »

Hi Martyn,

PicoScope 6.14.61.6219, and no I've got range set to 20v/div. The probes I'm using are Pico Technology TA375 x1/x10 probes rated at 600v in case that's a concern.

Thanks, Brett

brettc
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Re: Possibly a newbie mistake involving x10 probes

Post by brettc »

Ohhhh, I just realised that if I set it to 50v/div, it now goes higher than 20v (my PSU only goes up to 30v but presumably it will max out at 50v rather than the previous 20v). Is there some way to change that clipping limit? One of the big things I measure is solenoid pulses which I need to see the on and off voltages but also get an idea of the flyback pulse, so using a higher voltage range isn't really practical.

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Re: Possibly a newbie mistake involving x10 probes

Post by Martyn »

The setting is not V/div it is the overall input range, so to see a 24V signal you need at least the +/-50V range.
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brettc
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Re: Possibly a newbie mistake involving x10 probes

Post by brettc »

Ohhhhhhhhhhhh. Ok, THAT makes more sense. Thanks heaps! I think I can work it out from there :)

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