Choosing a USB DMM and software - Page 1
Forum section: electronics / testgear

author: SLJ
author_rank: Frequent Contributor
timestamp: March 03, 2013, 08:33:30 pm
content: I have been looking for a mid range DMM that I can connect to a USB port. The only thing the DMM would be for is the probe interface to the on screen display. I want something up to $150 US. I see quite a few DMMs with a USB interface but none seem to give any screen shots of what the software display on the monitor would look like.I will mostly be monitoring 1-400 DC volts, 0-250 AC volts, and 0-3 amps. I don't need high accuracy. I have bench Flukes for that. I just want something that will give me an on screen display and maybe a time line/logging for monitoring levels and changes over time. True RMS is not necessary but would be nice. My biggest concern is finding a DMM and software with a graphical display. Does not even have to be a handheld. The box could even be software driven but it's not necessary.Any suggestions of what has worked for you and maybe a screen shot of what's available?

author: M. András
author_rank: Super Contributor
timestamp: March 03, 2013, 09:11:07 pm
content: try to download the agilent dmm software, its free from their website and runs without a meter connected

author: mariush
author_rank: Super Contributor
timestamp: March 03, 2013, 09:33:03 pm
content: Uni-T UT61E is a 22.000 count multimeter with True RMS for about 60$By default it comes with a serial connection to the pc but you can easily use a 3-5$ rs232 to usb adapter to connect it to the PC, I use such adapter and it works great.It measures twice a second on any setting, sends to pc twice a second, has free software AND is also supported by UltraDMM (that has a thread on this forum about it, and you can download it freely)Downsides (if you can call them that) :* in rare cases, usually when its autorange code changes between internal ranges, it's possible to show a single measurement that's higher than normal then immediately reports the correct value (so for half a second it shows a bad value)... this is shown in the video review below. Basically if you log the measurements to a file, they jump out and can be easily spotted and removed so it's not a big issue* no backlight ,* no auto power off (but runs on 9v battery and gives accurate measurements as low as 3-4 volts, so you can change it to something else if you want to),There are hacks published that enable power off or backlight, if you'd ever be inclined to mod it.There's a huge thread about this meter on this forum here:https://www.eevblog.com/forum/reviews/uni-t-ut61e-multimeter-teardown-photos/There's an extensive video review of the meter here:presentation, construction, dc voltage accuracy,the PC data logging software, UltraDMM software, mains measurement, continuity , also shows that minor issue with the value being reported incorrectly for ONE measurement in some casesinside , teardown , battery consumption and how low can it go before turning off , it doesn't show incorrect values even on low batterytemperature stability, calibration etc

author: Lightages
author_rank: Unknown
timestamp: March 03, 2013, 10:48:02 pm
content: Quote from: SLJ on March 03, 2013, 08:33:30 pmI am not sure what you mean by that.

author: SLJ
author_rank: Frequent Contributor
timestamp: March 03, 2013, 10:56:10 pm
content: Just means I don't need the stand alone dmm. Some just make a box with prob jacks that connects via USB and all controls and ranges are software driven from the keyboard. Not usually found in this price range though.Screen shots of the computer display would be good. I've see the screen shot of the software for the Uni-T UT61E.

author: IanB
author_rank: Super Contributor
timestamp: March 03, 2013, 11:11:16 pm
content: Quote from: SLJ on March 03, 2013, 08:33:30 pmI have generally avoided USB interfaces and chosen RS232 style serial interfaces.Mainly because a serial interface overall is more flexible. I am comfortable with writing software and if the provided application doesn't do what I need I can write my own. Often the protocol is documented, and when it isn't it can usually be decoded. It is also easier to connect serial interfaces to old computers or micros. Programming against USB interfaces without a library is much harder.My favorite meter for this purpose is the venerable Radio Shack 22-812. I wrote some software that can log data from 1, 2, 3 or many of these simultaneously, which the original software cannot do.This meter has many advantages. The protocol is documented, the meter is inexpensive, and the battery power consumption is miserly, so you can leave the meter logging for hours at a time without consuming the battery.

author: Unknown
author_rank: Unknown
timestamp: March 03, 2013, 11:15:00 pm
content: Many meters have the pc protocol documented, either by the manufacturer, or reverse engineered. This allows you to interface it with custom software. Many more expensive meters also ship with LabView drivers, which allows you to easily develop your own GUI, assuming you already own a license.

author: IanB
author_rank: Super Contributor
timestamp: March 04, 2013, 02:17:37 am
content: Quote from: alm on March 03, 2013, 11:15:00 pmLabView has a horrible smell of $$$. As a hobbyist I don't think that is a solution I would be interested in.

author: SLJ
author_rank: Frequent Contributor
timestamp: March 05, 2013, 11:30:10 pm
content: Thanks for all the info and the link to the videos. I'm going to check out Ultra DMM. Looks more like what I'm looking for in software. From the videos I don't think I'd be happy with the Uni-T UT61E meter itself.

author: Rick Law
author_rank: Super Contributor
timestamp: March 08, 2013, 06:19:14 am
content: Quote from: mariush on March 03, 2013, 09:33:03 pmActually, the over/under-shoot is not so rare. In-so-far as I can discern (and I tested it over 100 times) it occurs when there is a range change. You will very likely see an over/under shoot if your measurement crosses the range barrier at rapid speed. By rapid speed, it means your measurement changes quickly.I rather like the way the UT61E works with a PC screen as the main display. There are two issues I found and one big plus:(1) When you are in REL mode, the PC receives data that is not delta-out. It may be possible in custom software to do the delta-out, but I am not sure it could be done. The meter acts faster than data transmission (2/sec), I have seen rapidly changing data displayed on the meter's LCD but not reflected on the PC display – it may be in the logged data but but not displayed. If it is not even in the logged data, that means the PC side does not know it. If you press REL while the meter is flexing between 1.01 and 1.02 ohms when REL is pressed, the last value before REL the meter received may or not may not be the one used by the meter to do delta-out.(2) I have no idea what the PC is reading when the meter is in PEAK mode. At first, I thought the PC was receiving the instantaneous reading. When I saw the number being unreasonable, I hooked up my other DMM and adjusted the voltage (what I was measuring) down. I then realize it is not an instantaneous reading. It is almost like an average since PEAK pressed, but I have not done the math (with logging data) to confirm if it is really an average.The big plus:The good thing about the standard RS232 interface: it is very easy to program a reader. I was able to put together some codes to dump the meter reading into a file in just a couple of hours even with some fancy reformatting included (to include the max error from the meter’s spec for that range). Not that I like to program my own, but I am preparing for a multi-day (probably mult-week) logging event and I expected the duration to be too long for the software to handle. The software UT provides doesn't log directly to file. It saves the data in a buffer and one can click to save the data to file. However big the buffer, the multi-day/week logging would likely exceed the buffer size.In fact, if I ever find my HP200LX (mini DOS machine with real RS232 port), I may modify my program to do more than logging, Apart from showing a better graph and a real MAX/MIN, I would add in a math function to convert the data (such as showing Watts for current when I know the volts), and show measurements with the error range, so I can see the reading is 1.2345 and the error range makes it 1.2331 to 1.2376 (or whatever it is appropriate for that range).I rather like the UT-61E. Fun little machine.Rick