isolated 4 channel 5.5 digit volt meter rs232 - Page 1
Forum section: electronics / testgear

author: ETITsynthesizer
author_rank: Contributor
timestamp: December 11, 2021, 12:36:47 am
content: I am looking to buy the cheapest isolated 4 channel 5.5 digit volt meter with rs232.I found this for $1795https://www.thinksrs.com/products/sim970.htmlthe chassis is $1595https://www.thinksrs.com/products/sim900.htmltotal $3390is there anything cheaper? all I see on ebay is grounded volt meters. I can get cheap grounded volt meters from china new in bulk but I would need to lift the ground. is it really a huge safety concern to lift the ground? the DC supplies are always isolated anyway. what could go wrong? if I use cheap chinese volt meters I think I can get 4 of them for $500 total shipped. they are stackable.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 11, 2021, 02:05:20 am
content: Even if you use floating supplies, The real ones are transformers related not smps (some say yes, others dont) nor buck boost convertersThe moment you connect grounds or the positive side on the dmm they became common in a way even if they have isolated channels ...Yes the price is high, but its conditionned to your special needsThe only others i know of :https://www.adcmt.com/en/products/dmm/7352Buying 4 separated meters could work, they must use isolation transformer, or one x-former with 4 independant outputs ??Use rs232 or usb isolators for the communication lines, you will have to manage 4 data sources, you have some free softwares links here who maybe could do the job ??What dou you want to measure with a setup like this ?

author: bob91343
author_rank: Super Contributor
timestamp: December 11, 2021, 02:31:11 am
content: What isolation voltage do you need? Ordinary gear is good to a couple of hundred volts.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 11, 2021, 02:19:18 pm
content: 4 separate multimeter would be a real option. There are 5.5. digit meters in the $500 range ( e.g. SDM3055, Rigol ... and a few more) . The interface would however be more like GPIB or ethernet.

author: threephase
author_rank: Regular Contributor
timestamp: December 11, 2021, 09:59:09 pm
content: Do you specifically need to see 4 displays at the same time, or could you use a data acquisition system with a DMM module and a multiplexer card?Rigol offer the M300 system circa £1,800 for chassis DMM module and multiplexer in the UK. Keysight, and Keithley offer options with an increased price.Depending on the voltage you require, there are also data logging systems from the likes of Graphtec. Cheaper for lower voltage requirements, but would be more for mains level voltages.

author: tautech
author_rank: Super Contributor
timestamp: December 11, 2021, 10:50:02 pm
content: Quote from: Kleinstein on December 11, 2021, 02:19:18 pmDepends entirely on the OP's voltage requirements which if not high can be satisfied with a single bench DMM with an inbuilt scanner card (multiplexer).For the SDM3055 adding the SC option permits measurement of 125VAC rms max with a max of 12 channels.http://siglentna.com/wp-content/uploads/2017/12/SC1016_Datasheet_DS60030-E02A.pdfBut the SC must be purchased with a new unit factory calibrated with the SC installed .... SDM3055-SC.At $ 728 it's a cost effective option.https://siglentna.com/digital-multimeters/sdm3055-5-%c2%bd-digits-dual-display-digital-multimeters/

author: ETITsynthesizer
author_rank: Contributor
timestamp: December 12, 2021, 03:32:16 am
content: Quote from: coromonadalix on December 11, 2021, 02:05:20 amthis looks like it is grounded on both inputs? I need differential measurement of voltage. I need to measure current also but I do that with a precision current sense resistor and convert the voltage to current in software.

author: ETITsynthesizer
author_rank: Contributor
timestamp: December 12, 2021, 03:34:00 am
content: Quote from: bob91343 on December 11, 2021, 02:31:11 amI am testing custom dual output DC power supplies. I need 4 differential voltage measurements < 20V each.

author: ETITsynthesizer
author_rank: Contributor
timestamp: December 12, 2021, 03:41:29 am
content: Quote from: tautech on December 11, 2021, 10:50:02 pmthis might work ok. if it is a single channel scanner, it doesn't matter that is earthed as long as that low side probe is also switched as part of the scanner. if it is a high side only scanner, that won't work because I have current sense resistors on the high side of the power supply under test. I need a differential measurement. My DC power supply under test is already isolated but I can't reference the same point 0V for all measurements.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2021, 03:48:49 am
content: Quote from: ETITsynthesizer on December 12, 2021, 03:41:29 amEach of the 16 channels are isolated and have 2 input connections.Have a study of the SC1016_Datasheet linked above.

author: graybeard
author_rank: Frequent Contributor
timestamp: December 12, 2021, 07:28:10 am
content: There are many scanning voltmeters available. They are sometimes call "data acquisition units." They use relays to independently connect many inputs to the input of the meter.I have used both Keysight and Keithley units. In my home lab I have a Keithley 2700 with a 20 input card I bought from a local electronics recycler.The best deal for a new one is the Siglent model Rob is suggesting. It's scanning rate is a bit slower than some of the competitors, but if it is fast enough for your needs it is the one I would buy today.You have to be careful when using any scanning voltmeter because the capacitance of the input and holds the voltage of the previous reading. Although the capacitance and charge is small it can cause transients to bounce back and forth on the cabling due to reflections. These transients do not usually compromise the readings because they dissipate quickly, but they can show up in the circuit being measured.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2021, 07:52:06 am
content: With a little imagination and ingenuity some nice creations have evolved to bring scanner card inputs to the front for more convenient everyday use.3DP Scanner card breakout from member pipe2nullhttps://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/msg3070270/#msg3070270

author: ETITsynthesizer
author_rank: Contributor
timestamp: December 12, 2021, 07:52:46 pm
content: the front panel shows the black probe connected to earth. are you saying that if I use the scanner that both probes are floating for a differential voltage measurement? again, it doesn't really matter because the device under test is an isolated DC power supply but it is preferable for me to buy a unit that makes differential voltage measurement without connecting earth to either of the probes.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2021, 07:56:28 pm
content: Quote from: ETITsynthesizer on December 12, 2021, 07:52:46 pmYes

author: Kean
author_rank: Unknown
timestamp: December 12, 2021, 08:10:58 pm
content: Quote from: ETITsynthesizer on December 12, 2021, 07:52:46 pmThe front panel of what?If you mean the SDM3055 (or pretty much any modern bench DMM) the inputs are isolated, and the front panel markings will show the maximum safe voltage between the terminals and isolation to earth.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2021, 08:14:17 pm
content: Quote from: Kean on December 12, 2021, 08:10:58 pmOP requires 4 isolated voltage measurements which can be done with the SDM3055 and 3065X bench meters with the Scanner card option:http://siglentna.com/wp-content/uploads/2017/12/SC1016_Datasheet_DS60030-E02A.pdf

author: Kean
author_rank: Unknown
timestamp: December 12, 2021, 10:42:48 pm
content: @tautech Yes I agree that is a good option.I have a couple of Agilent 34970A's and a Keysight 34972A, all with multiplex cards that acheive the same functionality (more in fact). Otherwise i'd probably buy an SDM3065X-SC myself.It doesn't explain his statement about front panel black probe connected to earth, which is what I was querying. It implies a misunderstanding somewhere.

author: bdunham7
author_rank: Super Contributor
timestamp: December 12, 2021, 10:57:25 pm
content: Quote from: ETITsynthesizer on December 12, 2021, 07:52:46 pmNo, you should have a closer look at those markings. The negative terminal is isolated from ground and they're telling you that isolation is good for 500V.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2021, 11:42:09 pm
content: Quote from: bdunham7 on December 12, 2021, 10:57:25 pmYes however that's only relevant to front panel connections, not for the Scanner card.

author: Kean
author_rank: Unknown
timestamp: December 13, 2021, 12:04:00 am
content: Quote from: tautech on December 12, 2021, 11:42:09 pmAre you sure about that?I don't think the isolation limit is due to the front panel connections themselves. I presume the "output" of the selected channel of the scanner card is isolated from the front panel connections, but the signals still route to the same internal circuitry that will most likely be what limits the isolation voltage to earth. The scanner card already has max voltage limits below what the front panel allows (e.g. 110VDC vs 1000VDC) which would be due to the PCB layout/relats/backplane connector.The SC1016 datasheet doesn't make the limits immediately clear like the front panel, but I think this is the relevant specification:Quote

author: ETITsynthesizer
author_rank: Contributor
timestamp: December 17, 2021, 03:42:49 am
content: Update: I looked at the keithley 2700, SDM3055-SC, SDM3065X-SC, Rigol M302.The keithley has RS-232 and GPIBThe Siglent units have Ethernet and USBThe Rigol has RS-232, GPIB, Ethernet and USBKeithley has two expansion portsSiglent has one expansion portRigol has 5 expansion ports but one is used for the DMM. so effectively 4 expansion ports.Kiethley 2700 + 2000-SCAN 6.5 digit $1300 for 10 differential voltage measurementsSiglent SDM3055-SC 5.5 digit $728 12 differential voltage measurements + 4 current measurementsSiglent SDM3065-SC 6.5 digit $988 12 differential voltage measurements + 4 current measurementsRigol M302 + M3TB20 6.5 digit $1852 20 differential voltage measurementsin summary the Rigol is king but the Siglent SDM3055-SC is probably good enough for what I need to do. for the $728 I think that price is the deciding factor.for a programmable load I found Multicomp MP710258 or MP710259 with RS-232, Ethernet, USBMy immediate need is to test a 40W power supply. for $250 the Multicomp MP710258 would work.

author: tautech
author_rank: Super Contributor
timestamp: December 17, 2021, 06:40:21 am
content: Quote from: ETITsynthesizer on December 17, 2021, 03:42:49 amAnd an optional USB-GPIB adapter:https://siglentna.com/product/usb-gpib-adapter/

author: Kleinstein
author_rank: Super Contributor
timestamp: December 17, 2021, 07:35:01 am
content: Besides the 2700, Keithley also as a DMM6500 variant with scanner. This would have a more modern UI. AFAIK the scanner cards are the same.

author: TurboTom
author_rank: Super Contributor
timestamp: December 18, 2021, 12:03:26 pm
content: If you want to use a scanner to apply the electronic DC load to several outputs of your DUT's sequentially as well, the M300 may still be the better choice, depending on the current that you need to switch. Rigol offers the "MC3416 Actuator" card that permits arbitrary interconnection by 16 SPDT channels in the same "frame" as the measurement system, provided 2A of current will suffice. The M300 offers quite a powerful, expandable infrastructure, albeit at a price.

author: ETITsynthesizer
author_rank: Contributor
timestamp: December 19, 2021, 02:02:15 am
content: it can switch 2A but I would need a 2A load in addition to the attenuator card. I need to load the power supply to 40W which is the rated output. that is a bit more than 2A at 12V or 15V. the multicomp programmable load is only $250 for 150W. I'm pretty sure it can switch between two precise currents in small increments. I'm happy to write python scripts to control things over different interfaces and different devices from different manufacturers.I went down the rabbit hole yesterday looking at thermocouples. the siglent can mux all 16 channels as 16 thermocouples or volt meters. this is better than the keithley that can only do one thermocouple and it requires a special more expensive thermocouple scanner card. this is about $300 more for that scanner card vs SCAN-2000. I'm now thinking that the siglent SDM3065X-SC is probably what I should get. I don't want to buy a 5.5 now and a 6.5 later. I just want to do this one time. notice the X is for thermocouple. SC is for scanner. this must be a factory option. no compatibility to add scanner cards to lower model SDM3065.https://siglentna.com/product/sdm3065x-sc/

author: tautech
author_rank: Super Contributor
timestamp: December 19, 2021, 02:18:34 am
content: Quote from: ETITsynthesizer on December 19, 2021, 02:02:15 amAll SDM3000 models work with thermocouples. The X designation was applied after SDM3055 was released and X was never added to that model to prevent confusion however the later X model bumper/feet upgrade was.All SC models have additional internal HW that supports the SC which is why they cannot be retrofitted.This HW consists of the physical support racking and sockets and looms for the electrical connections.

author: eevcandies
author_rank: Regular Contributor
timestamp: December 23, 2021, 10:53:00 am
content: Are you testing bench supplies? Why would you need 5.5 digits to test a bench supp1y? That would have to be a pretty high precision power supply! Just wondering.Thinking you could use four low cost wireless bluetooth multimeters and write up a PC app.