Author Topic: Accurate Low Amp Current Probe Advice  (Read 17969 times)

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Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #125 on: November 02, 2024, 08:47:06 pm »
As I mentioned before, you set 10mV/div, 1:1 and 50Ohm on the scope itself and leave it as it is.
Everything else (bandwidth limitation, scaling, AC, DC) is set on the 503B.

Quote
I set the SDG2122X output to 369mV at 1kHz, and that measured 5.00mA on my SDM3065X.

So you used a 73.8 ohm resistor as a load?

A piece of copper wire with some insulation on it.
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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #126 on: November 02, 2024, 09:04:37 pm »
I see, so you use the scope's internal 50 ohms as a load and connect the generator to the scope with this copper wire?

Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #127 on: November 02, 2024, 09:12:45 pm »
I see, so you use the scope's internal 50 ohms as a load and connect the generator to the scope with this copper wire?

No, I connected the copper wire between the positive/negative grabbers on the cable from the AWG. Then ran that through the current clamp. I also tried the same way with a 100Ω resistor, but I guess I'm doing it wrong. 😉
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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #128 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.

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?

Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #129 on: November 02, 2024, 09:40:29 pm »
Quote
No, I connected the copper wire between the positive/negative grabbers on the cable from the AWG.

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?

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
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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #130 on: November 02, 2024, 09:59:09 pm »
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.

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.

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Re: Accurate Low Amp Current Probe Advice
« Reply #131 on: November 02, 2024, 10:01:14 pm »
Quote
No, I connected the copper wire between the positive/negative grabbers on the cable from the AWG.

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?

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
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......
Avid Rabid Hobbyist.
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Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #132 on: November 02, 2024, 10:15:20 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.

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

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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #133 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.

Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #134 on: November 02, 2024, 10:37:45 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.

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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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #135 on: November 02, 2024, 10:41:27 pm »
Stick with the 1A DC, set the 503 to 0.2A/div and close all the measurement orgies on the scope so that you only see the screen.

Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #136 on: November 02, 2024, 10:53:51 pm »
Stick with the 1A DC, set the 503 to 0.2A/div and close all the measurement orgies on the scope so that you only see the screen.

I assume this is about what should be expected at 200mA/DIV?
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Re: Accurate Low Amp Current Probe Advice
« Reply #137 on: November 02, 2024, 10:55:24 pm »
If you could now set the scope to 10mV/div...
 
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Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #138 on: November 02, 2024, 10:57:04 pm »
If you could now set the scope to 10mV/div...

I did and changed the image faster than you replied. 😉😉
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Re: Accurate Low Amp Current Probe Advice
« Reply #139 on: November 02, 2024, 11:02:55 pm »
OK,
Except for the ripple, it looks good.
Now leave the settings on the scope as they are (except timebase, set it to say 1ms/div)and reduce the current, while simultaneously reducing the sensitivity on the 503.
e.g. 500ma current, 100mA/div on the 503.
Then 250mA, 50mA/div and so on.
 
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Re: Accurate Low Amp Current Probe Advice
« Reply #140 on: November 02, 2024, 11:15:09 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.
Remember about the interference from the transformer affecting performance of DC loads at these current levels... IOW: I don't think the clamp is broken, it is the test setup.

@KungFuJosh: Test the DC level with a battery and resistor. This way you eliminate all the unknowns that may be introduced by DC load and/or PSU. Secondly, measure the current using a shunt resistor. At low currents in the tens of mA range, a 1 Ohm resistor is a good choice and will give a solid foundation to base an conclusions on.
« Last Edit: November 02, 2024, 11:32:47 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #141 on: November 02, 2024, 11:21:21 pm »
OK,
Except for the ripple, it looks good.
Now leave the settings on the scope as they are (except timebase, set it to say 1ms/div)and reduce the current, while simultaneously reducing the sensitivity on the 503.
e.g. 500ma current, 100mA/div on the 503.
Then 250mA, 50mA/div and so on.
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Re: Accurate Low Amp Current Probe Advice
« Reply #142 on: November 02, 2024, 11:31:27 pm »
I see that you keep going “out” with the vertical zero line, is the ripple that big?
Now you would have to test whether it is the load, as Nico had already posted.
I will do the same with my Siglent load and a power supply “tomorrow”, I “only” have the AM503A, but that doesn't matter in this case.
 
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Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #143 on: November 02, 2024, 11:48:30 pm »
I don't have a THT 1Ω resistor handy, so I used a 100Ω resistor connected to a 9V battery. In series with the SDM3055X-E it measured 82mA.

10mA/DIV on the current amp.
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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #144 on: November 02, 2024, 11:50:14 pm »
Quote
In series with the SDM3055X-E it measured 82mA.

Then please set 503 to 20mA/div....
 
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Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #145 on: November 02, 2024, 11:57:57 pm »
Quote
In series with the SDM3055X-E it measured 82mA.

Then please set 503 to 20mA/div....

I did that too, and it looked the same except the mean was about 39mV. I could do it again and screen capture it if you want.
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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #146 on: November 02, 2024, 11:59:58 pm »
That would be nice, because I want to be able to see the zero line on the scope.

Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #147 on: November 03, 2024, 12:03:56 am »
That would be nice, because I want to be able to see the zero line on the scope.

I switched to a 1.21k resistor to lower the current. SDM in circuit shows 7.19mA.

Here the current amp is set to 5mA/div. What should I actually set it to? 😉

Thanks,
Josh
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Online Martin72

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Re: Accurate Low Amp Current Probe Advice
« Reply #148 on: November 03, 2024, 12:29:44 am »
As I said, I will make a short clip later in which I measure various currents with my Tek System.
If you get it into your head that nothing more needs to be set on the scope except for the basic condition, the rest only on the 503, then it will be easier to work with.
At the moment, it's just a matter of determining whether your Tek System is working properly.
And we will find that out later.
 
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Offline KungFuJoshTopic starter

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Re: Accurate Low Amp Current Probe Advice
« Reply #149 on: November 03, 2024, 12:54:41 am »
The inside of the amp doesn't look too bad. The stickers think it was last calibrated in 2014, and the "cal void if cut" stickers were already cut.
« Last Edit: November 03, 2024, 01:00:55 am by KungFuJosh »
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