Communication protocol for UT171 - Page 1
Forum section: electronics / testgear

author: Pumuckl
author_rank: Newbie
timestamp: February 09, 2021, 11:58:56 am
content: Hi,I am planning on buying a couple of hand held UT171 multimeters to use for automated tests. The meters are connected via USB-IR cables to a pc or laptop running labview. I am reading actual value, min, max, avg and also control stuff like the range or reset the min/max reading. Has anyone come across a documentation of the communication protocol used in these UNI-T meters?Best regards,Christian.PS: At the moment I use 2 Fluke 187 and several 287/9 meters. The 187 work quite good, I can control the stuff I need to like min, max range etc. and the connection is pretty reliable. The 287 meters are just a headache to control. The protocol is proprietary and Fluke has only documented a few basic commands. This is inconvenient but still allows me to do all the things I have to by a combination of manual and automated operation. The biggest problem is that the meter uses the same interface like the 187 but at 20x the baudrate. It seems that the interface is not quite up to the task and I often loose data. If I have enough time I can reset the interface and read the data again but for some tests this is not an option.

author: justanothername
author_rank: Regular Contributor
timestamp: February 09, 2021, 12:23:20 pm
content: I'm using the UT61E for automated tests with this python library:https://github.com/4x1md/ut61e_py/tree/master/srcWorks flawlessly, but it is receive only.

author: Pumuckl
author_rank: Newbie
timestamp: February 10, 2021, 03:06:04 pm
content: Thanks for the link, this is a good starting point for writing a labview driver. I still hope you can at least send keypress commands to the meter to set and reset the min/max measurement. I did contact UNI-T support, but I don't have high hopes. If they provide some info I make sure to let you guys know.

author: PKTKS
author_rank: Super Contributor
timestamp: February 10, 2021, 03:39:04 pm
content: UNI_T DMM mostly boils down to the cable used...so far* Most UNI-T DMMs can be used with two (three) different PC interface cables:* - The UT-D04 USB/HID cable, old version with Hoitek HE2325U chip.* - The UT-D04 USB/HID cable, new version with WCH CH9325 chip.* - The UT-D02 RS232 cable.Drivers are already written and working in libsigrok sources..interesting side note is that on the RS232 cables - as of today -we will just rely instead on the interface chip used.. beingCH341 or FTDI or PLxxx - so far FTDI seems far better supported.Paul

author: Pumuckl
author_rank: Newbie
timestamp: February 15, 2021, 11:38:58 am
content: Thanks for the hint with the libsigrok library.I did some more digging but I could not find the meter listed in the supported hardware. The only mention I could find is in the "EEVBlog 121GW" page where it states that these meters use the same chipset. Is it the same as the UT71 models regarding communication? What I figured out until now is that you can read from these meters but you will not be able to control them (reset min/max/avg reading). If this is true then it will not be usable for me.From what I could find this morning, I the UT181 could probably do what I need. Has anyone used this meter and also controlled it via the interface? It seems there are commands for everything you could do with the switches on the meter itself. Since I do not need all that logging stuff I would rather have a simple meter but it seems that there is not much that has comparable current accuracy to the Fluke meters.If anyone knows a meter with really good current accuracy and min/max/avg reading where you can also reset the reading via the interface please let me know...Christian.

author: Bad_Driver
author_rank: Frequent Contributor
timestamp: March 17, 2021, 10:30:01 am
content: Hi Pumuckl,I own now for some weeks a UT181a and I'm very happy with it. I have done some checks in the VDC and VAC ranges with my HP 34401aand it seems better than the specs. And it shows reliable values in VAC up to 600....800 kHz compared to the 34401a.The only downside I found (compared to the Fluke 289) - there is no way to compensate the thermal probes error of about 2 degrees andthe low battery time of 40 hours before recharging. If you have no other equipment your logging time is restricted to this 40 h. You can not usethe meter while charging. But this makes sense for me, you should better not charge the meter during 400V logging for safety reasons.I have not checked if there is a "wake up" mode for the meter to measure every 10 min or so without draining the battery all the time.(seems to be possible with the Fluke).But the UT181a is much faster and has a beautiful OLED display compared to the Fluke.There is a command line tool for reading the UT181a via the USB-connector for further postprocessing. If you are interested I post the link tomy web finding. I can also do some current measurements against the HP. What range you are interested in?