UNI-T UT181A

UNI-T UT181A

Status	supported
Source code	uni-t-ut181a
Counts	60000
IEC 61010-1	CAT IV (600V) / CAT III (1000V)
Connectivity	UT-D09 (USB) / UT-D07A (BLE)
Measurements	voltage, current, resistance, capacitance, frequency, duty cycle, period, diode, continuity, temperature, gain
Features	autorange, true-rms, data hold, min/max/avg, peak, relative, bargraph, backlight, logging
Website	uni-trend.com

The UNI-T UT181A is a 60000 count 0.025% accuracy logging digital multimeter with PC connectivity.

See UT-D09 and UT-D07A for typical cables.

Users need to enable communication in the meter's menu system before starting the application (SETUP -> Communication -> ON).

Hardware

• Cyrustek ES51997 analog frontend (2Sa/s for 60000 counts, 10Sa/s for 600 counts; 60MOhm, 60nS, 60mF, 60mHz, 5-95%)
• STM32F103... MCU (serial protocol is rather different from devices which share the DMM chipset)
• ST flash (512KiB?)
• ISSI SRAM 1Mx16
• 24C256 EEPROM
• DS2086 RTC
• RAiO display controller
• colour dotmatrix display
• 14 push buttons, range selector
• split terminals in current probe plugs ("lead error")
• 7.4V 2200mAh accumulator
• CR2032 coin cell
• bidirectional IR communication
• ships with UT-D09 USB cable, UT-D07A BLE is an option

Photos

• 

  PCB, DMM chipset and MCU with memory

• 

  PCB, MCU and memory

Protocol and usage

The external MIT licenced ut181a project (written in the Rust programming language) also contains a description of the protocol, see the Resources section below. Development of the sigrok driver greatly benefited from this protocol description.

The choice of a serial cable and the meter's specific protocol are independent from each other.

Quick test of the UT-D09 cable:

 $ sigrok-cli --list-serial
 ...
 $ sigrok-cli -d uni-t-ut181a:conn=hid/cp2110 --scan
 The following devices were found:
 uni-t-ut181a:conn=hid/cp2110 - UNI-T UT181A with 5 channels: P1 P2 P3 P4 bar

Listing the device's features and current state:

 $ sigrok-cli -d uni-t-ut181a:conn=hid/cp2110 --show
 Driver functions:
     Multimeter
     Thermometer
 Scan options:
     conn
     serialcomm
 uni-t-ut181a:conn=hid/cp2110 - UNI-T UT181A with 5 channels: P1 P2 P3 P4 bar
 Supported configuration options:
     conn: hid/cp2110 (current)
     continuous: on, off
     limit_frames: 0 (current)
     limit_samples: 0 (current)
     limit_time: 0 (current)
     data_source: Live (current), Save, REC_00, REC_12, REC_4, REC_5, REC_6, ..., REC_19, REC_20
     datalog: on, off (current)
     measured_quantity:  - supported measurements:
       voltage/ac
       voltage/dc (current)
       voltage/ac/dc
       gain
       current/ac
       current/dc
       current/ac/dc
       resistance
       conductance
       continuity
       voltage/dc/diode
       capacitance
       frequency
       duty_cycle
       pulse_width
       temperature
     range: auto (current), 60mV, 600mV, 6V, 60V, 600V, 1000V, 600uA, 6000uA, 60mA, 600mA, 20A, 600Ω, 6kΩ, 60kΩ, 600kΩ, 6MΩ, 60MΩ, 60nS, 6nF, 60nF, 600nF, 6uF, 60uF, 600uF, 6mF, 600mF, 60Hz, 600Hz, 6kHz, 60kHz, 600kHz, 6MHz, 60MHz, 1000°C, 1832F

Reading measurements, and recordings:

 $ sigrok-cli -d uni-t-ut181a:conn=hid/cp2110/raw=/dev/hidraw0 --samples 4
 FRAME-BEGIN
 P1: 3.527 mV DC AUTO
 bar: 2 mV DC
 FRAME-END
 FRAME-BEGIN
 P1: 3.527 mV DC AUTO
 bar: 2 mV DC
 FRAME-END
 FRAME-BEGIN
 P1: 3.527 mV DC AUTO
 bar: 2 mV DC
 FRAME-END
 FRAME-BEGIN
 P1: 3.527 mV DC AUTO
 FRAME-END

 $ sigrok-cli -d uni-t-ut181a:conn=hid/cp2110/raw=/dev/hidraw0 --continuous -c data_source=Save
 FRAME-BEGIN
 P1: 28.3 °C
 P2: 28.4 °C MAX
 P3: 28.3 °C AVG
 P4: 28.2 °C MIN
 FRAME-END
 FRAME-BEGIN
 P1: 23.3 °C AUTO
 P2: 24.5 °C
 FRAME-END
 FRAME-BEGIN
 P2: 17.31 mV DC MAX
 P4: -39.01 mV DC MIN
 FRAME-END
 FRAME-BEGIN
 P1: 1.357 mV DC REL
 P2: 0 µV DC REF
 P3: 1.357 mV DC
 bar: 1 mV DC
 FRAME-END
 FRAME-BEGIN
 P1: 3.292 mV DC
 bar: 3 mV DC
 FRAME-END
 FRAME-BEGIN
 P1: -60.00 dBV AUTO
 P2: 1.0 mV AC
 bar: 0 V AC
 FRAME-END
 FRAME-BEGIN
 P1: 0.00 dBV REL
 P2: -60.92 dBV REF
 P3: -60.92 dBV
 bar: 0 V AC
 FRAME-END
 FRAME-BEGIN
 P1: 0.00 dBm REL
 P2: -53.19 dBm REF
 P3: -53.19 dBm
 bar: 0 V AC
 FRAME-END
 FRAME-BEGIN
 P1: -54.77 dBm AUTO
 P2: 0.5 mV AC
 P3: 75 Ω
 bar: 0 V AC
 FRAME-END

Usability, Handling of the meter

• range selector does "rough" function selection, "gets amdended" by more MENU items which heavily depend on current mode (relative, min/max, peak; volt/amp plus frequency, ac+dc, low pass filter, gain, dual temperature or difference, short/open circuit, etc)
• save (single shot) or record (series at given interval) initiated from SAVE menu
• comparison (limits check) initiated from COMP menu
• unfortunate choice of UI colour scheme, dark red on black, hard to tell from a 6 o'clock viewing angle which menu item is active (or unfortunate display orientation? 12 o'clock works much better)
• always shows current mode's main reading even when navigating menus or viewing saved/recorded measurements including trend charts
• builtin help on push button operation (single page, hold info button)
• serial communication is OFF after each power cycle, needs to get re-enabled after each start
• keeps (main) function across power down (because OFF is not a range selector position)
• cannot measure when charging builtin accumulator
• can charge without the wall plug (if shipped with the wrong type for the region), feed some 10V 500mA from a PSU to the COM and mA receptables

Resources

• ut181a DMM library and ut181a-cli application
• UT181A protocol description
• eevblog pictures and ESD robustness threads
• joeqsmith testing meters, series of videos, among them comparing Uni-T UT181A to Fluke 289 and others, including electrical robustness tests