UNI-T UT71x series

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UNI-T UT71x
Ut71c mugshot.png
Status supported
Source code serial-dmm
Counts 20000/40000
IEC 61010-1 CAT III (1000V) / CAT IV (600V)
Connectivity RS232 / USB
Measurements voltage, resistance, diode, continuity, capacitance, frequency, duty cycle, current, temperature, power (only UT71E), loop current (not on UT71B)
Features autorange, hold, peak hold, relative, min/max, bargraph, backlight, true-rms
Website uni-trend.com

The UNI-T UT71x is a series of 20000/40000 counts, CAT III (1000V) / CAT IV (600V) handheld digital multimeters with RS232 or USB connectivity.

Devices

Device Conrad OEM Tenma OEM Counts Comments
UNI-T UT71A Voltcraft VC-920 20000
UNI-T UT71B Tenma 72-7730 20000
UNI-T UT71C 40000
UNI-T UT71D Voltcraft VC-960 (?) Tenma 72-7732 40000
UNI-T UT71E Voltcraft VC-940 Tenma 72-9380A 40000

The PCB markings for this series are not necessarily useful, most devices read "UT71A" (even for devices which are not an UT71A). However, there is usually a white sticker on some IC which correctly identifies the DMM ("B", "E", "920", or the like). There's usually also a hand-drawn marking (e.g. "B" or "C") on the PCB itself.

Protocol

The devices use a simple 11-byte protocol over a USB-to-serial or USBHID-to-serial link (depending on the cable used).

The communication parameters are 2400 baud, 7o1. However, the vendor software opens the serial port with 8n1 settings, so the vendor protocol descriptions are slightly off. Also, the available vendor protocol descriptions from e.g. Conrad are partially incomplete or even erroneous in some places.

Byte Description Comments
0 Digit 1
1 Digit 2
2 Digit 3
3 Digit 4
4 Digit 5
5 Range
6 Function
7 State 1
8 State 2
9 \r (0x0d)
10 \n (0x0a)

The following information is not available/sent via the protocol (and is thus unavailable for sigrok purposes):

  • the REL, MIN, MAX, HOLD flags
  • the bargraph value
  • the backlight status
  • the low-battery indicator
  • the internal measurement value store (only available on some models)

Resources