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Accurate Low Amp Current Probe Advice

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Martin72:
Hi,


--- Quote ---Right now I have the PSU supplying 18V with no current limit. The ET load is set to draw 30mA. The current probe is on the negative lead with the arrow pointing towards the PSU negative, as the manual shows.
--- End quote ---

I would then proceed as follows:
- As I said, set the scope to 10mV/div and 1:1 coupling, 50 Ohm DC
- Set the following on the AM503:
5mA/div, make sure that none of the Probe Open lights up, make sure that “DC” is lit - Because after switching on, the AM503 is always set to “REF” and you can't see anything on the scope....
And before you put the current clamp in the line, do a auto-degaussing.
At 30mA and 5ma/div on the AM503, you should set the vertical line on the scope to the last division (5mA times 6 boxes).
Try it out first before we worry about the conversion on the scope.

tautech:

--- Quote from: KungFuJosh on November 02, 2024, 09:40:29 pm ---
--- Quote from: Martin72 on November 02, 2024, 09:17:44 pm ---
--- Quote ---No, I connected the copper wire between the positive/negative grabbers on the cable from the AWG.
--- End quote ---

That would be a direct short circuit and you don't know how the SDG handles something like that (current limiting).
I would continue trying with the right resistors.
Or you have your ET load, use that first to see if the clamp is working properly.
Since the button was off the clamp:
Did you make sure that no “Probe open” indicator was lit on the AM503B?

--- End quote ---

I switched to DC with the ET load already, but I don't know what I should set things as. So how would you do it?

It's the AM503B, so I can set specific mA/DIV values (1,2,10,20,50,100 etc.)

I want to see what the low end is that this can measure, but I'm having trouble getting it to do anything in that range without lots of guessing.

How would you set this up? Tell me everything from the current amplifier to the scope and trigger settings. I know the scope settings are supposed to be 10mV/DIV, but why can't we change the display to A on the modern scope? There must be settings we can use related to the settings on the current amplifier?

Right now I have the PSU supplying 18V with no current limit. The ET load is set to draw 30mA. The current probe is on the negative lead with the arrow pointing towards the PSU negative, as the manual shows.

Thanks,
Josh

--- End quote ---
Been thinking about too this as my Siglent active current probe is soon to arrive....

SDG models can supply 200mA......
If we set one for DC supply and some V output into an appropriate load we can measure/check the current drawn from the SDG using a meter we have on hand and trust.
Then check our current probes are displaying similar values......

Then check again with waveforms activated......

KungFuJosh:

--- Quote from: Martin72 on November 02, 2024, 09:59:09 pm ---I would then proceed as follows:
- As I said, set the scope to 10mV/div and 1:1 coupling, 50 Ohm DC
- Set the following on the AM503:
5mA/div, make sure that none of the Probe Open lights up, make sure that “DC” is lit - Because after switching on, the AM503 is always set to “REF” and you can't see anything on the scope....
And before you put the current clamp in the line, do a auto-degaussing.
At 30mA and 5ma/div on the AM503, you should set the vertical line on the scope to the last division (5mA times 6 boxes).
Try it out first before we worry about the conversion on the scope.

--- End quote ---

I (think) I did all of that, and this is what I'm getting. I set to -60mV on the position so the wave would be visible. It's triggering off AC instead of the DC signal.

30mA current draw of the load is confirmed with the SDM in circuit showing 29.9mA.

Thanks,
Josh

Martin72:
WTF.... :o

Off the top of my head, I would say that either the current clamp or the AM503B module is defective – it should be a straight line, just DC current.
But let me recreate this at my place tomorrow and make a short clip of how I set it up.
If you can't do it exactly the same way, something is defective.

KungFuJosh:

--- Quote from: Martin72 on November 02, 2024, 10:22:09 pm ---WTF.... :o

Off the top of my head, I would say that either the current clamp or the AM503B module is defective – it should be a straight line, just DC current.
But let me recreate this at my place tomorrow and make a short clip of how I set it up.
If you can't do it exactly the same way, something is defective.

--- End quote ---

I assume there's AC interfering with the DC current, but the frequencies are goofy (to me, who knows nothing 😉). The measure counter shows frequencies around 85Hz, then it jumps to 667Hz with that test.

Now I'm trying 1A DC to lose whatever AC is below that, but it seems like maybe the amplifier is an issue. I have it set to 100mA/div and the scope is showing about 85mV, and the frequencies are jumping around in the low kHz range.

Maybe the filter caps in the current amp need to be replaced? Or maybe I'm doing something dumb. I dunno. I'll try AC again with a 100Ω resistor.

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