UNI-T UT71x series

UNI-T UT71x

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

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

• UNI-T: UT71 series overview
• Conrad protocol descriptions: VC-920, VC-940, VC-960