Author Topic: New Keithley DMM6500 and now DAQ6510  (Read 104067 times)

0 Members and 1 Guest are viewing this topic.

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #600 on: July 29, 2019, 06:37:10 pm »
I would love if someone else could confirm my findings, since I still really don't know if it is just isolated to my particular unit.  There really is nothing I can find to explain the behavior, and my test setup is identical between two different meters.

Also, there is of course no problem measuring current or voltage separately (meaning either a connection to the Amp input or to the HI input, but not both simultaneously).
 

Offline Hugoneus

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: us
    • The Signal Path Video Blog
Re: New Keithley DMM6500 and now DAQ6510
« Reply #601 on: July 29, 2019, 06:45:55 pm »
here is the setup and pics below.
How exactly do you connect the device?
For 6500 there is a limit: "Sense terminals on inputs are limited to 10 V range during ratio measurement."

No sense terminals are used.  The circuit diagram shows the connection points, and the polarity of the measurements in the pictures confirms which terminals I used.

Here are some pics.  Hopefully the wire colors make it clearer.

I will try this with the DAQ tonight.
 
The following users thanked this post: JxR

Offline Hugoneus

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: us
    • The Signal Path Video Blog
Re: New Keithley DMM6500 and now DAQ6510
« Reply #602 on: July 30, 2019, 01:47:24 am »
I tried the same thing as your setup. Both with a battery and with a power supply. I could not replicate the issue. The instrument reports the correct results.
 
The following users thanked this post: thm_w, Mr. Scram, JxR

Offline cozdas

  • Contributor
  • Posts: 38
Re: New Keithley DMM6500 and now DAQ6510
« Reply #603 on: July 30, 2019, 01:58:04 am »
I would love if someone else could confirm my findings, since I still really don't know if it is just isolated to my particular unit.  There really is nothing I can find to explain the behavior, and my test setup is identical between two different meters.

Also, there is of course no problem measuring current or voltage separately (meaning either a connection to the Amp input or to the HI input, but not both simultaneously).

I wonder if this has something to do with the relay timings and/or measurement delays. Have you tried with different integration times (NPLC, repeat filters etc)?
 

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #604 on: July 30, 2019, 03:18:30 am »
I wonder if this has something to do with the relay timings and/or measurement delays. Have you tried with different integration times (NPLC, repeat filters etc)?

There are no relays switching during the testing, except when you manually choose the 100V range (no relay switching occurs on the 1A/3A/10A ranges with simultaneous measurements).  NPLC/filter has no effect.  You do not have to technically even be doing a simultaneous measurement,  it will occur only measuring voltage.  But the circuit has to be wired up to do a simultaneous V/I measurement: Common LO, amp input near the low side of circuit, HI input where appropriate.  Anyways, alot of people here have actual DMM6500, and it is a simple enough circuit to duplicate.

It can of course be done using a power supply and electronic load as well, just better to make sure you are pulling around 1A or above.  It is not really apparent at all if you are only drawing say 1mA.
« Last Edit: July 30, 2019, 01:34:25 pm by JxR »
 

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #605 on: July 30, 2019, 03:22:04 am »
I tried the same thing as your setup. Both with a battery and with a power supply. I could not replicate the issue. The instrument reports the correct results.

Dr. Shahriar, your pictures both show 10V range, and it only occurs when you select the 100V range.  Did you happen to try manually going to the 100V range?  I really appreciate you trying this out.
 

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 471
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #606 on: July 30, 2019, 03:56:19 am »
Very strange! Can you check (with a separate meter across the battery) if  DMM6500 is reporting incorrect voltage? Presumably that is the case since the current does not change as you switch the voltage range.

If so, it could be a error in their switch matrix for different ranges. My guess: 100V range usually gets divided by 100 before ADC, so the actual voltage measured is about 0.09V. Somehow a fraction of the current burden voltage gets subtracted from it.
« Last Edit: July 30, 2019, 04:15:23 am by maxwell3e10 »
 

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #607 on: July 30, 2019, 04:16:06 am »
Very strange! Can you check (with a separate meter across the battery) if  DMM6500 is reporting incorrect voltage? Presumably that is the case since the current does not change as you switch the voltage range.

If so, it could be a error in their switch matrix for different ranges.

Yes this has already been done with 3 different meters.  Only the DMM6500 that is doing the simultaneous measurement shows the problem.

Anyways here is an example using two SMUs to source 15V and sink ~1A, the DMM6500 to do a simultaneous measurement, and the DMM7510 to measure the voltage.  Same problem occurs with only the DMM6500.

798360-0
« Last Edit: July 30, 2019, 01:34:06 pm by JxR »
 
The following users thanked this post: hwj-d

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 471
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #608 on: July 30, 2019, 04:24:26 am »
Thanks. Its clear that  either your meter has a bad FET or Keithley screwed up this fairly basic configuration.
 
The following users thanked this post: JxR

Offline cozdas

  • Contributor
  • Posts: 38
Re: New Keithley DMM6500 and now DAQ6510
« Reply #609 on: July 30, 2019, 05:05:08 am »
There are no relays switching during the testing, except when you manually choose the 100V range (no relay switching occurs on the 1A/3A/10A ranges with simultaneous measurements).  NPLC/filter has no effect.  You do not have to technically even be doing a simultaneous measurement,  it will occur only measuring voltage.  But the circuit has to be wired up to do a simultaneous V/I measurement: Common LO, amp input near the low side of circuit, HI input where appropriate.  Anyways, alot of people here have actual DMM6550, and it is a simple enough circuit to duplicate.

It can of course be done using a power supply and electronic load as well, just better to make sure you are pulling around 1A or above.  It is not really apparent at all if you are only drawing say 1mA.

I see. I don't have DMM6550, I only have DMM6500 but tried a similar setup with it (I used separate current and voltage sources).

I see the same problem: In DC voltage mode if you pass some current through the amps-common connectors, the voltage is misreported. Passing 1A through the amps terminal causes ~ -45mV error in voltage measurement in 10V range, and ~-2.6V error in 100V and 1000V ranges. Halving the current causes the voltage measurement error to halve too.

There seems to be a cross-talk from amps circuit in voltage mode indeed.
 
The following users thanked this post: thm_w, Mr. Scram, JxR

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #610 on: July 30, 2019, 05:09:50 am »
I see the same problem: In DC voltage mode if you pass some current through the amps-common connectors, the voltage is misreported. Passing 1A through the amps terminal causes ~ -45mV error in voltage measurement in 10V range, and ~-2.6V error in 100V and 1000V ranges. Halving the current causes the voltage measurement error to halve too.

There seems to be a cross-talk from amps circuit in voltage mode indeed.

Thank you.  I really appreciate you confirming this for me.  My guess is that Keithley knows something is wrong as well, but the lawyers are not allowing them to talk to us about it.  Still it would be nice to have a couple more people confirm the same problem with their units as well.
 
The following users thanked this post: maxwell3e10

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 471
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #611 on: July 30, 2019, 05:24:47 am »
If this is a problem for all DMM6500 meters and even exists to a significant extend on the 10V (and perhaps other) ranges, its a fairly major flaw. Its surprising it took over a year since the instrument was introduced to discover it. These boards really help to ferret out the flaws.
 

Offline cozdas

  • Contributor
  • Posts: 38
Re: New Keithley DMM6500 and now DAQ6510
« Reply #612 on: July 30, 2019, 05:30:41 am »
Here is the simplified bug repro steps for people to test it (Edit: even simpler steps)
- switch to DC volts, 100V range
- short the Input High and Input Low: you should read ~0V on the display
- While still in DCV mode pass DC 1A through the Amps-Input Low terminals: Now you will read a large value (-2.6V in my case)

I also tested with the rear terminals: If you use the rear 10Amp therminal, the error in voltage reading is around only -5mV in all ranges. Rear 3Amp terminal behaves the same as the front terminals: -2.6V error for 1A in 100V range.

therefore the workaround is:
If you need to pass current through the DMM while measuring voltage use the rear 10Amp terminal. This will reduce the voltage reading error significantly.
« Last Edit: July 30, 2019, 06:04:12 am by cozdas »
 
The following users thanked this post: maxwell3e10

Offline Mike G

  • Contributor
  • Posts: 14
Re: New Keithley DMM6500 and now DAQ6510
« Reply #613 on: July 30, 2019, 05:31:01 am »
Hi, thanks to everyone for highlighting this serious problem. I have just checked and my 6500 exhibits the same problem. There is indeed a small (but totally unnacceptable) error introduced on the 10v range and an enormous error on the 100v and 1000v ranges, the meter certainly is not within spec under these conditions. I will try to upload a couple of pictures later today.
Regards all, Mike
 

Offline Hugoneus

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: us
    • The Signal Path Video Blog
Re: New Keithley DMM6500 and now DAQ6510
« Reply #614 on: July 30, 2019, 06:36:24 am »
I couldn't fall asleep, so I went and tried it again.

I can confirm that I see the problem with the DAQ6510 as well. At 1A there is an offset of -2.6V present in the 100V range and about 80mV in ranges < 100V.

I will discuss this with my Keithley support contact.
 
The following users thanked this post: thm_w, msliva, cozdas, BU508A, hwj-d, Mr. Scram, JxR

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #615 on: July 30, 2019, 06:39:03 am »
I couldn't fall asleep, so I went and tried it again.

I can confirm that I see the problem with the DAQ6510 as well. At 1A there is an offset of -2.6V present in the 100V range and about 80mV in ranges < 100V.

I will discuss this with my Keithley support contact.

Thanks for checking again and confirming.  I have to say I was kind of hoping the DAQ wouldn't have the problem as well.
 

Offline Hugoneus

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: us
    • The Signal Path Video Blog
Re: New Keithley DMM6500 and now DAQ6510
« Reply #616 on: July 30, 2019, 06:41:58 am »
I couldn't fall asleep, so I went and tried it again.

I can confirm that I see the problem with the DAQ6510 as well. At 1A there is an offset of -2.6V present in the 100V range and about 80mV in ranges < 100V.

I will discuss this with my Keithley support contact.

Thanks for checking again and confirming.  I have to say I was kind of hoping the DAQ wouldn't have the problem as well.

Both the DMM and DAQ have the same architecture, so it makes sense that they share the issue. I am curious as to why the DMM7510 doesn't have this problem.

I wonder if this can be fixed in firmware; I am skeptical, because the instrument normally can't tell if there is current going through the other terminal without switching some relays at low current ranges.

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 471
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #617 on: July 30, 2019, 06:46:26 am »
I also tested with the rear terminals: If you use the rear 10Amp therminal, the error in voltage reading is around only -5mV in all ranges. Rear 3Amp terminal behaves the same as the front terminals: -2.6V error for 1A in 100V range.
If the error is present at some level on all current and voltage ranges it suggests a problem with the ground reference point. This might not be so easy to fix. Even a 5 mV error is well outside the spec on most ranges. I wonder if it says in the manual somewhere that simultaneous current flow and voltage measurements are not allowed. Or perhaps in the process of simplifying the design of the DMM7510 they went a bit too far.
 

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #618 on: July 30, 2019, 06:59:20 am »
If this is a problem for all DMM6500 meters and even exists to a significant extend on the 10V (and perhaps other) ranges, its a fairly major flaw. Its surprising it took over a year since the instrument was introduced to discover it. These boards really help to ferret out the flaws.

I reported the problem back on page 21 about 1.5 months ago, and started engaging with Keithley about the problem at the same time.  I think the fact that they went completely silent and refused to continue to communicate with me after I sent them a video I recorded fully demonstrating my setup and the problem speaks volumes.  They must have confirmed the problem but don't currently have a solution to it.

I didn't want to make a fuss about it since I never knew until now if it was just my unit or not.

This might not be so easy to fix. Even a 5 mV error is well outside the spec on most ranges. I wonder if it says in the manual somewhere that simultaneous current flow and voltage measurements are not allowed.

Secondary measurements are feature of the device and I never remember reading anything that would imply such a problem.
« Last Edit: July 30, 2019, 07:12:30 am by JxR »
 

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 471
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #619 on: July 30, 2019, 07:27:09 am »
When measuring current, one should sense voltage directly across the current shunt. When measuring voltage, one should sense voltage directly across input terminals. One possibility is that they "saved" on one switch that moves the ground reference of the ADC from one point to the other, so it now includes a voltage drop across some internal traces.
 

Offline The Soulman

  • Frequent Contributor
  • **
  • Posts: 697
  • Country: nl
  • The sky is the limit!
Re: New Keithley DMM6500 and now DAQ6510
« Reply #620 on: July 30, 2019, 07:44:59 am »
When measuring current, one should sense voltage directly across the current shunt. When measuring voltage, one should sense voltage directly across input terminals. One possibility is that they "saved" on one switch that moves the ground reference of the ADC from one point to the other, so it now includes a voltage drop across some internal traces.

That sounds like it.
 

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #621 on: July 30, 2019, 07:50:07 am »
When measuring current, one should sense voltage directly across the current shunt. When measuring voltage, one should sense voltage directly across input terminals. One possibility is that they "saved" on one switch that moves the ground reference of the ADC from one point to the other, so it now includes a voltage drop across some internal traces.

I thought I remember someone where in this thread the shunt resistor values were confirmed.  Although not sure where exactly that was.  Maybe that would help you with your theory.
 

Offline imo

  • Super Contributor
  • ***
  • Posts: 2589
  • Country: 00
Re: New Keithley DMM6500 and now DAQ6510
« Reply #622 on: July 30, 2019, 08:43:01 am »
A year back this poster showed similar results - aprox 0.3V/1Amp.
With 100V range aprox 3V/1A then?

https://www.eevblog.com/forum/testgear/new-keithley-dmm6500/msg1781402/#msg1781402
« Last Edit: July 30, 2019, 08:47:49 am by imo »
 

Offline JxR

  • Supporter
  • ****
  • Posts: 268
  • Country: us
Re: New Keithley DMM6500 and now DAQ6510
« Reply #623 on: July 30, 2019, 08:47:09 am »
A year back this poster showed similar results - aprox 0.3V/1Amp.

https://www.eevblog.com/forum/testgear/new-keithley-dmm6500/msg1781402/#msg1781402

I don't any problem at all on the 1V range, which all those pictures indicate.  Doesn't appear related unless I'm missing something.
 

Offline The Soulman

  • Frequent Contributor
  • **
  • Posts: 697
  • Country: nl
  • The sky is the limit!
Re: New Keithley DMM6500 and now DAQ6510
« Reply #624 on: July 30, 2019, 08:54:34 am »
Does anyone have link to the manual that shows this setup?
Couldn't find it myself.
I'm curious to know how this is supposed to work with a shared common terminal without introducing errors.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf