Keithley DMM6500 recording Two Measurements  - Page 1
Forum section: electronics / testgear

author: gogoman
author_rank: Regular Contributor
timestamp: November 14, 2022, 02:01:42 am
content: Hello, I have not used a Keithley DMM6500 and was wondering can the DMM6500 record both voltage and temperature. if so what is required to do so. Would the DAQ6510 be a better choice.The voltage ands temperature is sample rate is 1 to 2 millisecond for a total time of 12hrs. I assume that the data will need to be dump to a host computer periodically.your input is appreciatedgogo

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: November 14, 2022, 06:28:08 am
content: Dear Gogoman,The DMM6500 is not primarily designed to do two measurements at once. As explained this the below video, it can do so to some degree, but dependent on the precise setting, this comes with limitations.https://youtu.be/Z7sYUL85jTcSo, I would not recommend purchasing the DMM6500 when the (main) use case is making several measurements at once. Having that said, the DMM6500 is a great and very flexible meter for single measurements!

author: Hydron
author_rank: Super Contributor
timestamp: November 15, 2022, 11:34:56 am
content: I'm assuming you want independent measurements of temperature and DCV? Not for instance the calculated temperature and the measured voltage of a thermocouple?If it's the former then you're out of luck unless you use a scanner card (and in ms range you'd need a solid state one, and I'm still not sure you could switch fast enough even then) or possibly using the DCV ratio function to read DCV off both the force and sense inputs (it can be configured to give more output info than just the ratio).The secondary measurement function only really works when:a) the measurement inputs are independent or somewhat so, e.g. DCV and DCI, Freq and ACVb) you don't need a range switch that uses a relay, unless you're happy to have it clicking away using up relay life (maybe OK for long integration times or for short-term use)c) you're not making a measurement where the use of one function can cause offsets in the other due to internal configuration (e.g. DCI and some DCV ranges)

author: MegaVolt
author_rank: Frequent Contributor
timestamp: November 15, 2022, 12:34:57 pm
content: Quote from: gogoman on November 14, 2022, 02:01:42 amIf I don't confuse anything. Dual measurement data is not available remotely.

author: thm_w
author_rank: Super Contributor
timestamp: November 15, 2022, 10:29:35 pm
content: Quote from: Hydron on November 15, 2022, 11:34:56 amTemperature measurements in the ms range, highly unlikely its actually needed but who knows..Quote from: MegaVolt on November 15, 2022, 12:34:57 pmIsn't secondary measurement just swapping back and forth? So reading one, changing then reading the other, via scpi, would be the same thing no?

author: gogoman
author_rank: Regular Contributor
timestamp: November 16, 2022, 07:07:53 am
content: hello, the voltage and temperature measurements are independent, with the temperature measurements made at a 250ms interval.The manual mentions a scanner card for temperature, therefore the front input terminals can be used for dc voltage and with scpi switching between the two.Does this make sense?" possibly using the DCV ratio function to read DCV off both theforce and sense inputs(it can be configured to give more output info than just the ratio" The manual did not mention force input did you mean input terminals, can you clarify DCV ratio function.thank gogo

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: November 16, 2022, 07:17:35 am
content: Just ignore this comment if you find it irrelevant, but I wonder whether other options would be (more) suitable for the use case you sketch. Like a PicoTech ADC-20 logger (20 bit) or ADC-24 (24 bit), and/or a TC-08 Data Logger (specifically designed for thermocouples, but has voltage input option as well). You can run those from a PC but also from, say, a Raspberry Pi, which might solve the need for in-between computer backup during your measurements (and the associated interruptions in measuring). And there is cloud support, too. Whether this is an option also depends on your signals, and whether you can pre-condition them for use with such a logger (if you intend to measure 600VAC then the story is different than for a DC range of -1 to 1 V ;-).

author: MegaVolt
author_rank: Frequent Contributor
timestamp: November 16, 2022, 08:50:45 am
content: Quote from: thm_w on November 15, 2022, 10:29:35 pmPerhaps this is so .... Have you seen a mention of this in the documentation?

author: thm_w
author_rank: Super Contributor
timestamp: November 16, 2022, 11:01:45 pm
content: Quote from: gogoman on November 16, 2022, 07:07:53 amhttps://www.tek.com/en/blog/measuring-power-using-your-keithley-dmms-ratio-functionBut I think as RBBVNL9 says, unless you have the DMM6500 already, if you are looking at a dedicated device, look at DAQs instead (labjack, NI, etc).Which will allow you to easily measure a number of temperatures and voltage inputs. Although usually to slightly lower accuracy than a 6.5 DMM.Quote from: MegaVolt on November 16, 2022, 08:50:45 amThere are two ADCs inside, but, one is not terribly accurate (16-bit digitizer). So any main measurement is done on the main ADC.But, as mentioned above there is that Ratio function that can measure the voltage on the Sense and Input terminals, simultaneously:https://www.tek.com/en/blog/measuring-power-using-your-keithley-dmms-ratio-functionSo maybe I'm wrong there.But if you are measuring simultaneous Voltage and Current, NOT using a shunt, its just going to be switching between the inputs and performing another conversion.

author: Kean
author_rank: Unknown
timestamp: November 17, 2022, 04:31:33 am
content: Quote from: thm_w on November 16, 2022, 11:01:45 pmAt 1000 readings per second you'd need to use 0.01 or 0.0005 NPLC settings and thus get 5.5 digits at best from the DMM6500.I'd suggest looking at the Labjack T7 or T7 Pro. I often use the older U3HV models for similar multi-channel long term logging, but at a much slower sample rate. Measuring 6 channels with scaling every second for several days.I have some 34970A's and a 34972A (similar to DAQ6510) but tend to use the LabJacks where possible to reduce wear on the relays. You can also get the LabJack PCBs as an OEM part to build into your own test fixtures.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: November 17, 2022, 09:27:03 am
content: Quote from: thm_w on November 16, 2022, 11:01:45 pmThe ratio measurement is performed by the main ADC and can be selected remotely. And also the data gets into two different buffers and can be requested remotely.QuoteYes, it is fast switching between inputs. But you cannot select dual measurement mode remotely. I didn't find any commands that allow you to do this. Those. mode you must select and configure manually.

author: Hydron
author_rank: Super Contributor
timestamp: November 17, 2022, 11:34:05 am
content: If you already have a DMM6500 just build or buy a scanner card for it, the hook both temperature and voltage measurement stuff to it and use that. Ideally use a voltage-output temperature transducer (e.g. TC and ref junction) so you're not needing to switch between measurement modes inside the meter as well. If you want fast switching then SSR based card is better (not sure if you can buy these or it's DIY only).Note that you cannot switch between front and rear inputs remotely (it's a physical switch), so everything needs to be connected to the scanner.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 17, 2022, 12:23:05 pm
content: A 1-2 ms time scale is quite fast, even for the electronic / photo-MOS switches. Especially the temperature is rarely needed that fast. One may get away with the DMM6500 reading voltage and another cheaper, slower meter to read the temperature.The hardware may be capable to do 2 measurements essentially simultaneous, but the software support is missing. The Keithley 2100 may have been the better option - that meter support dual measurements, especially thermocouple plus something else.