UNI-T UT71x series
 | |
| 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
- UNI-T: UT71 series overview
- Conrad protocol descriptions: VC-920, VC-940, VC-960