Author Topic: Siglent SDM3045X mA current measurement - weird behaviour  (Read 10134 times)

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Offline ahopeTopic starter

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Siglent SDM3045X mA current measurement - weird behaviour
« on: November 04, 2018, 03:02:29 pm »
My Siglent 3045X is behaving odd when measuring  < 600mA.

I was trying to measure current consumption of an STM32F030K6 when I discovered some behaviour. Instead of the expected 3-6 mA current, it displayed about 10% of that - 5-800 uA.
I started to investigate. My two other multimeters showed the expected 3-6 mA, so I was starting to worry my siglent was totally out of spec.
Using my bench supply and a test setup with the 3045X, the current display on the bench supply and a handheld multimeter and a load I started testing from 3A down.
All meters were in agreement until I went below 600mA - then the 3045X would switch from the 6A scale to 600mA scale. This is where the really weird thing happens.
It will show the correct value, say 0.053 A, then switch to the 600mA scale and show 53.4 mA for about a second, then I hear a relay click and suddenly the display will be 6.58 mA.
Playing around and switching scale manually this is totally repeatable for small currents below a few hundred mA. The 600mA and lower scales will show values about 1/10 of actual current. The 6 and 10A scales are ok.

What is really freaking me out is that when manually changing scales down, it will show the correct value and scale for a second before a relay kicks in and ruins everything.

Anyone have any idea what is happening and how to fix?

The meter is a bit over a year old. A few months ago I blew the internal 10A fuse which I replaced myself. Otherwise the meter has been sitting on my bench since new.


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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #1 on: November 04, 2018, 07:07:49 pm »
My Siglent 3045X is behaving odd when measuring  < 600mA.

The meter is a bit over a year old.
Welcome to the forum.

Since then there has been a firmware update to V5.01.01.03.
Can you confirm the firmware version you're running ?
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Offline ahopeTopic starter

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #2 on: November 04, 2018, 07:25:25 pm »
The firmware version was one of the first things I checked. I am running the latest  5.1.1.3. I was hoping for something more recent, its over a year old.

It could be firmware - in fact, it does look like it could be a firmware bug since it first displays the correct range and value before kicking in that relay and ruining everything.

But still looking for a resolution..
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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #3 on: November 04, 2018, 07:33:44 pm »
The firmware version was one of the first things I checked. I am running the latest  5.1.1.3. I was hoping for something more recent, its over a year old.

It could be firmware - in fact, it does look like it could be a firmware bug since it first displays the correct range and value before kicking in that relay and ruining everything.

But still looking for a resolution..
OK, I'll shoot your findings through to tech support. Might take a day or so for an answer.
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Offline ahopeTopic starter

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #4 on: November 04, 2018, 07:46:05 pm »
Thanks. This one has me totally baffled.
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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #5 on: November 08, 2018, 02:58:59 am »
After some discussion and trials in conjunction with tech support we have a suggestion for you to try.

PM sent.
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Offline ahopeTopic starter

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Re: Siglent SDM3045X mA current measurement - weird behaviour - video
« Reply #6 on: November 08, 2018, 07:15:55 pm »
I now tried full reset to factory, reinstall software (latest) to no avail.

With any current < 2-300 mA it will display the same behaviour.
-With manual scale it will  show correct current (checked with 2 other multimeters) on the 6A scale. Switching to 600mA scale or below it will show correct value for about 1 sec, then you can hear a "click" and it will display a value of about 12% of correct value.
-With automatic scaling this will happen when you drop below 600 mA, it will switch to 600mA scale, show the correct value for a second, then "click" and off she goes.

Without any good ideas next step is return to siglent or rip the darned thing open and troubleshoot myself.
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Offline BillB

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #7 on: November 09, 2018, 12:26:11 am »
I've also got a 3045X running v5.1.1.3.  I replicated the tests with a 3055 inline as well and experimented with both auto and manual ranging.  I couldn't get it to fail selecting the proper range, or the proper value when manually selecting another range.  :-//

It does take that second to switch ranges.  I'm wondering it you are seeing the correct value in the old range (6A) before the click and the switch to the new range?
« Last Edit: November 09, 2018, 12:39:37 am by BillB »
 
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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #8 on: November 09, 2018, 12:39:48 am »
I've also got a 3045X running v5.1.1.3.  I replicated the tests with a 3055 inline as well and experimented with both auto and manual ranging.  I couldn't get it to fail selecting the proper range, or the proper value when manually selecting another range.  :-//
Thanks heaps for checking this Bill.  :clap:
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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #9 on: November 09, 2018, 12:43:27 am »
I have one more thing for ahope to try; this time a hidden reset that I will share by PM.

It should not produce a different result to the one sent previously but we're running out of suggestions.  :(
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Offline ArthurDent

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #10 on: November 09, 2018, 01:06:09 am »
I suspect that when the meter switches current ranges there may be different value current shunts switched in. Say on the 10A range it is .1 ohm, on the 600Ma range it is 1 ohm, and on the 60Ma range it is 10 ohms. (I just guessed, I don't know what your instrument has for range and shunt values). If you are putting a resistance in series with your power supply and your load, the voltage drop across the meter may be too high on the lower ranges to allow your circuit under test to receive the proper voltage. Different multimeters will have different values so one might work while another might not.

Use a second voltmeter and try reading the actual voltage the device is receiving after the it goes through the ammeter. Switch the current ranges and see what effect that has on the voltage.
 

Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #11 on: November 09, 2018, 02:16:17 am »
The meter is a bit over a year old. A few months ago I blew the internal 10A fuse which I replaced myself. Otherwise the meter has been sitting on my bench since new.
I've heard of this once before, ie. the internal fuse opening before the one on the back panel.

Do you remember the style of internal fuse, eg. fast blow, glass or ceramic ?

What is the fuse in the rear panel ?

From the datasheet:
http://www.siglentamerica.com/wp-content/uploads/dlm_uploads/2017/10/SDM3045X_Datasheet_DM0545_E01A.pdf

Internal :12 A, 250 V slow-melt fuse
Rear panel : accessible 10 A, 250 V fast-melt fuse

Which makes me question why the internal fuse should open first.  :-//
Could they be installed incorrectly ?
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Offline Performa01

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #12 on: November 09, 2018, 04:27:13 am »
If there was a probem with the fuses, there would be no reading at all. More specifically, we would not see a correct reading in the Amp ranges.

The problem has to be with the shunt resistors:
0.01 Ohm for the Amp ranges (6A, 10A)
0.1 Ohm for mA ranges (60mA, 600mA)
1 Ohm for the lowest ranges (600µA, 6mA)

@ahope, have you tested the 6mA range and does it fail as well?

If just the 60mA and 600mA ranges are off, then something might be wrong with the 0.1 Ohm shunt resistor.
If the 6mA range fails as well, then I would suspect a problem with the relays for the range switching and/or some serious contamination (lump of solder?) on the PCB.

I do not think this is a calibration issue because the error is so massive.

 

Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #13 on: November 09, 2018, 07:25:39 pm »
OK so ahope tried what I sent him with zero result.  :(

So where we are behind the scenes in discussions with Siglent.
This has been escalated to the product manager and technicians and they are checking possible scenarios.

There is suspicion of an analog board problem, yes of course and I have some ideas of just what.
Now it's Sat at the factory so we won't get a reply until Mon (your Sun).

2 immediate possibilities in my mind; damage to relay contacts or one of the shunts.
Thoughtful testing should easily confirm.

One suspects the over-current/blown fuse event caused this...........but it shouldn't have !  >:(
The 10A FB rear panel fuse should open first......not the 12A SB on the PCB.  :-//



ahope, make another post or 2 to get your count above 5 so full member privileges become available.
« Last Edit: November 09, 2018, 07:32:16 pm by tautech »
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Offline ahopeTopic starter

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #14 on: November 09, 2018, 08:07:11 pm »
Hi guys,

Thanks for all the suggestions.

I ran through some more tests now, and the error is persistent from about 250mA down.

If I set it to 600mA and then gradually reduce the current it will show correct values until i go below approx 230mA. Then the relay clicks, display is reduced with about 88% and will stay that way all the way down to microAmps.

I am quite sure its a relay kicking in another shunt resistor that causes this. Question is what will cause the relay to trigger at the wrong time/current?

Still working on this, will have a look inside tomorrow.
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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #15 on: November 09, 2018, 08:26:27 pm »
Just try and find/identify the problem......relay contacts/operation or damaged shunt.
It will be good for the Siglent engineers and other members to know what it is so we know if to repair or it's a warranty claim.
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Offline ahopeTopic starter

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #16 on: November 09, 2018, 11:12:59 pm »
Did some more investigation.

First, took the lid off and did a visual inspection.
Then I tried to locate which relay was kicking in. It seems like all of them are kicking in simoultaneously, but at least the big white in the read box is kicking in.

After looking around I found one resistor that looked bad - look inside the red box.

In the next picture I have a close-up. Its  R408 marked "SMT F0705 R010".
From the picture it looks like a burn-mark on one side and you can see it is bulging up in the middle.
Resistor R407 next to it looks like it may be a little non-flat, but not so easy to see.

Both these resistors are close to the big white relay, and next to that is the 12A fuse that blew a while ago.

Could this be the culprit?
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Offline ahopeTopic starter

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #17 on: November 09, 2018, 11:30:34 pm »
Another thingvthat bothers me: why did the internal fuse blow and not the external? and why didi it not protect the internals?
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Offline Performa01

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #18 on: November 10, 2018, 12:05:04 am »
Nothing wrong with R408. It is the 0.01 Ohm shunt that works flawlessly in the amps range. That "burn mark" at the side comes from some milling for trimming its resistance value - I'm actually baffled that Siglent goes to the effort to do this on a low cost instrument like this.

But the photos also show that my assumption was wrong and there are only two shunt resistors, just as stated (not very clearly) in the datasheet. The only other shunt resistor is R407 at 1 Ohm.
 
According to the data sheet, this 1 Ohm resistor would be active for the 600mA range, but the very same data sheet also states a burden voltage of <0.5V in the 600mA range, which cannot be true because 600mA * 1 Ohm = 0.6V (plus voltage drop across cabling, fuse and connectors).

Anyway, R407 looks good as well and also from the latest symptom description it is unlikely that the shunt is at a fault. If the meter works correctly in the 600mA range down to some 230mA, then the shunt resistor should be okay.

The real problem is the relay(s) switching below 230mA - whichever they are, in any case throwing off the measurement.

 

Offline bson

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #19 on: November 10, 2018, 01:36:51 am »
Verify that it can measure low voltages correctly, like maybe 5-10mV down to whatever you can produce reliably (50µV maybe).
 

Offline ahopeTopic starter

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #20 on: November 10, 2018, 08:35:13 am »
First,

Thanks for the suggestion to vheck volt measurement. I set up a simple voltage divider and verified it with two hand-held DMMs.
The 3045X measured the same values (+/- a few % since it should be way more accurate than the cheap DMMs). The values I tested were 5mV and 0.5mV.

The meter would work normal on both auto-range and manual range.  The measurements were made on the 600mV range.

So the voltage side of the 3045X seems to be operating normal and within spec.

Back to the R408. From what I can see it is clearly bulging up. There is no smooth top surface on it, more like it has been "blown" up. Is this normal? You should be able to see it if you study the pictures.
« Last Edit: November 10, 2018, 08:38:23 am by ahope »
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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #21 on: November 10, 2018, 08:51:32 am »
Hmmm, yes it looks like that shunt has been hurt.  :(

Hunting around I found a couple of images of 3045X and 3055 and enlarged (that didn't work. Grrr) them......attached.
« Last Edit: November 10, 2018, 08:53:29 am by tautech »
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Offline HKJ

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #22 on: November 10, 2018, 09:00:56 am »
The shunt has been damaged, but if the meter measures correctly it is not that serious yet, but maybe the reading will change with time when air has access to the shunt element.

 
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Offline tautech

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #23 on: November 10, 2018, 09:05:25 am »
The shunt has been damaged, but if the meter measures correctly it is not that serious yet, but maybe the reading will change with time when air has access to the shunt element.


Your one is not trimmed.  :o

Thanks for the pic.  :-+
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Offline HKJ

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Re: Siglent SDM3045X mA current measurement - weird behaviour
« Reply #24 on: November 10, 2018, 09:16:58 am »

Your one is not trimmed.  :o


I do not believe in laser trimming in this meter, electronic calibration is much easier and cheaper.
 


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