Author Topic: New Keithley DMM6500 and now DAQ6510  (Read 104069 times)

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Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #625 on: July 30, 2019, 09:01:19 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.

I don't remember there being any diagram for a measurement setup demonstrating the dual V/I measurement.  Regardless, you pretty much have to do your current measurement on the low side after your load, and your HI input closer to the source.  I made a diagram of the measurement I made using a battery which should be a page back at the most.

https://www.eevblog.com/forum/testgear/new-keithley-dmm6500/msg2578767/#msg2578767
« Last Edit: July 30, 2019, 09:04:07 am by JxR »
 
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Offline The Soulman

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #626 on: July 30, 2019, 09:38:06 am »
Found yours, There you show two separate gnd lines from the voltage and the current meter, in reality
it is one and any voltage drop on it (caused by the current flow) wil add (or subtract rather) to your
voltage reading.
Inside the meter there is also voltage drop on the current shunt and fuse also introducing error unless
 they switch around the gnd-ref point for the adc.

Dave's 121gw also has a similar "feature".
 

Offline imo

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #627 on: July 30, 2019, 09:52:32 am »
What you get if the Voltage is secondary?
« Last Edit: July 30, 2019, 09:59:34 am by imo »
 

Offline KedasProbe

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #628 on: July 30, 2019, 10:55:05 am »
I guess the problem will be similar when I tried to measure the voltage drop
https://www.eevblog.com/forum/testgear/new-keithley-dmm6500/msg2427312/#msg2427312
For the 100mA ranges there was a relays switching that made the readings wrong:

This was the given explanation:
Ah, my bad on not explaining this, the relay switching will cause brief discontinuities in the AMPS terminal so the Rigol that's not synced to the switching would measure a higher resistance.  If you hook a scope up to the terminals you should be able to see this.  The discontinuity happens because voltage measurements happen while the current range relay is in the 1A/3A position.  So if the relay isn't already in that position it will be forced there.  I'm not totally sure all the reasons that position is required, but I believe part of it is to prevent noise from reaching the voltage measurement circuitry. 

So anyway, it's best to use the 1A/3A ranges if you want to continuously measure burden voltage with this method.


Maybe an old firmware should be tested to see if it was introduced later or if it was always like that.
« Last Edit: July 30, 2019, 10:58:16 am by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #629 on: July 30, 2019, 01:57:36 pm »
Found yours, There you show two separate gnd lines from the voltage and the current meter, in reality
it is one and any voltage drop on it (caused by the current flow) wil add (or subtract rather) to your
voltage reading.
Inside the meter there is also voltage drop on the current shunt and fuse also introducing error unless
 they switch around the gnd-ref point for the adc.

Dave's 121gw also has a similar "feature".

Are you referring to my little circuit drawing for the test from the battery?  It was just a drawing and there is only a single reference point to ground regardless of how many wires I showed.  Either way, I showed actual pictures of the wires from the DMM and connected to the battery, there really shouldn't be any confusion.

As to the voltage drop across the test leads, we are talking about 40mOhm leads here.  The drop across them is completely insignificant compared to the 2.6-2.8V drop we are seeing at 1A.  It is arguing that the number should be 2.56V instead of 2.60V.

Sorry if I'm misunderstanding what you are trying to say, pretty tired atm.
« Last Edit: July 30, 2019, 02:08:04 pm by JxR »
 
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Offline KedasProbe

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #630 on: July 30, 2019, 03:41:21 pm »
Hi,

I tested it with my DMM6500 but I simplified the schematic a little (yes that's possible)
I just connected a current source to the DMM6500 and shorted the voltage terminals with 50 Ohm.
So I should get 0 Volt all the time:

I got this: no sound, sorry, when the voltage changes to -2.47V instead of -36mV, it is still -36mV on the terminals.



edit: one more thing I didn't have a relays sound on 100V range (the same like lower ranges)
edit2:
When no resistor is connected then for 1.00A I get -21mV for voltage (and much more in the 100v range and up)
When I short the voltage terminals I get -38mV (and again much more for 100V range and up)
« Last Edit: July 30, 2019, 06:53:19 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
[W. Bruce Cameron]
 
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Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #631 on: July 30, 2019, 03:53:30 pm »
Hi,

I tested it with my DMM6500 but I simplified the schematic a little (yes that's possible)
I just connected a current source to the DMM6500 and shorted the voltage terminals with 50 Ohm.
So I should get 0 Volt all the time

Nice demonstration.  Thanks. 

Edit: I did see about the same sourcing 1A from one of the SMU when I tried.  I like this method, but I wanted to post what I thought was simpler: a 9V battery and a 10Ohm resistor.  I would guess that a lot of people don't actually have a precision current source (but have batteries and voltage sources) and my goal was to have as many people as possible test their DMM6500. 
« Last Edit: July 30, 2019, 06:27:19 pm by JxR »
 

Offline maxwell3e10

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #632 on: July 30, 2019, 06:57:21 pm »
This is a good general test setup: flow 1 A into current input, short out the voltage input and measure the voltage. It would be interesting to test DMM7510 and other meters in this way to measure the internal common terminal voltage drop. It depends  on details of construction, can be different for front vs. rear terminals.

In DMM6500 it seems they make a mistake of connecting the 100:1 voltage divider to the common before the current shunts.  This has the effect of amplifying the voltage drop by a factor of 100 on 100V and 1000V ranges.
 

Offline KedasProbe

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #633 on: July 30, 2019, 07:00:36 pm »
Edit: I did see about the same sourcing 1A from one of the SMU when I tried.  I like this method, but I wanted to post what I thought was simpler: a 9V battery and a 10Ohm resistor.  I would guess that a lot of people don't actually have a precision current source (but have batteries and voltage sources) and my goal was to have as many people as possible test their DMM6500.
I'm pretty sure anyone with a DMM6500/DAQ6510 has a power supply with max. current protection.
That's what you see in my video, the max current protection doing its job.
« Last Edit: July 30, 2019, 07:03:34 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
[W. Bruce Cameron]
 

Offline maxwell3e10

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #634 on: July 30, 2019, 07:05:00 pm »
OK, let's not argue. JxR gets the credit of finding this flaw after a lot of people used the meter for a year.
 

Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #635 on: July 30, 2019, 07:26:01 pm »
I'm pretty sure anyone with a DMM6500/DAQ6510 has a power supply with max. current protection.
That's what you see in my video, the max current protection doing its job.

Cool.  My mistake, and I didn't actually try it this way myself.  But yeah its essentially the same as using a dedicated current source.

Overall, I guess I'm glad I am no longer alone with the flaw since it tells me I'm not crazy ;D ...but then again it would have been better if it was only my unit since I could have just sent it in for warranty service and no one would have to suffer with me.

I guess the next question is what should we do about it.  All start requesting warranty service from Keithley for our meters? 
 

Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #636 on: July 30, 2019, 07:30:36 pm »
OK, let's not argue. JxR gets the credit of finding this flaw after a lot of people used the meter for a year.

I certainly don't think about it this way.  If I'm going to be honest I was a tad frustrated that no one was willing to do the test a ~month ago when I first said something.  Although, that is on me for not being more vocal about it, providing more data, and test scenarios.  I guess I felt that I was still new to the forum and didn't want to be a prick about it.  Keithley refusing to talk to me about it also kind of messed with mind.

I'm a career IT and have only been playing at EE for a few years now.  Most of you are way more knowledgeable than I am and I'm just glad your here to help me out.
« Last Edit: July 30, 2019, 07:54:03 pm by JxR »
 

Offline maxwell3e10

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #637 on: July 30, 2019, 07:50:24 pm »
I just tested Keysight 34470 in this way. It has an -81 mV offset for 1 A current on 3 A terminal  and -4mV offset on 10 A terminal. But these numbers don't change on any voltage ranges.
 

Offline KedasProbe

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #638 on: July 30, 2019, 07:50:46 pm »
I guess the next question is what should we do about it.  All start requesting warranty service from Keithley for our meters?
Simple we push until we get a good answer. ;)
You will see I added the link of the tek forum in the description of the youtube video.
It's their support forum they should use it wisely.

Could be one of the reasons why their latest firmware update is delayed.
Not everything that counts can be measured. Not everything that can be measured counts.
[W. Bruce Cameron]
 

Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #639 on: July 30, 2019, 07:59:15 pm »
Simple we push until we get a good answer. ;)
You will see I added the link of the tek forum in the description of the youtube video.
It's their support forum they should use it wisely.
Thanks. I put in a reply to the topic as well.

Could be one of the reasons why their latest firmware update is delayed.
I admit I have wondered about this myself.
« Last Edit: July 30, 2019, 08:21:22 pm by JxR »
 

Online Kleinstein

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #640 on: July 30, 2019, 08:38:33 pm »
There probably is nothing that can be done about it - it kind of a HW point. It is quite normal to have the actual central ground point at the "negative" side of the shunt chain. So there is a drop to the common terminal and this is measured. The unusual point is having the divider connected the way to get the extra signal.  Anyway, when there is a current flowing, the voltage reading is no longer valid. This could be annoying when using the dual measurement mode. Anyway a shared terminal should also be suspicious.
 

Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #641 on: July 30, 2019, 08:42:34 pm »
I just tested Keysight 34470 in this way. It has an -81 mV offset for 1 A current on 3 A terminal  and -4mV offset on 10 A terminal. But these numbers don't change on any voltage ranges.

The DMM7510 was -35mV on the 3A terminal in all voltage ranges, and -3.5mV in all voltage ranges on the 10A terminal with a 1A source.
 
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Offline JxR

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #642 on: July 30, 2019, 08:55:48 pm »
Anyway, when there is a current flowing, the voltage reading is no longer valid. This could be annoying when using the dual measurement mode. Anyway a shared terminal should also be suspicious.

I would certainly not argue against your expertise in the matter, but why should we expect the meter not to perform as specified when doing dual measurements?  It is a feature of this meter and documented in the manual.  The only warning in the manual concerning dual measurements has to do with wear on the relays.
 

Offline maxwell3e10

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #643 on: July 30, 2019, 09:28:02 pm »
I just tested Keysight 34470 in this way. It has an -81 mV offset for 1 A current on 3 A terminal  and -4mV offset on 10 A terminal. But these numbers don't change on any voltage ranges.
The DMM7510 was -35mV on the 3A terminal in all voltage ranges, and -3.5mV in all voltage ranges on the 10A terminal with a 1A source.
Maybe somebody can test an HP3458 in this way for reference.

There probably is nothing that can be done about it - it kind of a HW point. It is quite normal to have the actual central ground point at the "negative" side of the shunt chain. So there is a drop to the common terminal and this is measured.
This is certainly the easiest way to do it, but on a meter that can do 4-wire Ohms measurement it should be possible to move the ground reference of the ADC closer to the input terminal.
 

Offline lukier

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #644 on: July 30, 2019, 10:27:11 pm »
Maybe somebody can test an HP3458 in this way for reference.

It is getting late here today, but maybe tomorrow I can try to do this test on my DMM6500 and two 3458As, as well as previous generation of Keithley (2015 and 2001).
 

Offline imo

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #645 on: July 30, 2019, 11:36:47 pm »
Possible explanation of the issue with the small 9V battery and the 10ohm resistor:

1. the first picture at 10V range shows
PRIM: 9V -> battery voltage when NOT LOADED by 10ohm
SEC: 0.87A -> the current when 10ohm connected to the battery

2. the second picture at 100V shows
PRIM: 6.7V -> battery voltage when LOADED by the 10ohm
SEC: 0.87A -> the current when 10ohm connected to the battery

My current understanding is the 10V range and 100V range differ in the way "when or how" they switch the internals in the measurement sequence.

Thus it is not a drop on the shunt or a 100V range defect, but the 6.7V is the voltage of the battery when loaded by the 10ohm. You may try to connect the 10ohm directly to the battery and measure the voltage at the battery.

« Last Edit: July 30, 2019, 11:55:18 pm by imo »
 

Offline cozdas

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #646 on: July 31, 2019, 12:23:01 am »
Thus it is not a drop on the shunt or a 100V range defect, but the 6.7V is the voltage of the battery when loaded by the 10ohm. You may try to connect the 10ohm directly to the battery and measure the voltage at the battery.

All of those possibilities are eliminated in the posts above. DMM reads -2.7V with the input Hi and Lo shorted when 1A passes through the amps terminal.
 
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Offline maxwell3e10

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #647 on: July 31, 2019, 01:07:28 am »
Most of these meters have DC Ratio function that measures separately voltage on sense terminals. So, one could setup an I-V function, where the voltage is measured by sense terminals and current is measured using the common and current terminals. This would eliminate the internal voltage drop problems.

However, since the maximum voltage range of sense terminals is 10V, it wouldn't allow higher voltage measurements that are particularly bad on the DMM6500
 

Offline Hugoneus

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #648 on: July 31, 2019, 02:59:32 am »
I tried two other meters:

Keithley 2015 THD: 14.5mV offset is observed on all scales. It is constant.
Keysight 34470A: 75mV offset is observed on all scales. It is constant.

I can try this on several other models (Keysight, Rigol, Siglent, etc.) if you guys really want to see.  :-//
 
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Online 2N3055

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Re: New Keithley DMM6500 and now DAQ6510
« Reply #649 on: July 31, 2019, 05:55:05 am »
I just tried on Rigol DM3068. 1A into Amp connector, set to volts, it is cca -15mV , all Volt ranges .
DM3068 doesn't have simultaneous I/V function.
MTX3293 shows 5mV, all ranges, it does have VA function.

Regards,
 
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