UNI-T UT181A

UNI-T UT181A

Status	planned
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

TODO

Protocol and usage

Currently there is no sigrok driver for the UT181A device. An external MIT licensed project which was written in the Rust programming language also contains a description of the protocol, see the Resources section below. This will be useful in the creation of a sigrok driver.

The choice of a serial cable and the meter's specific protocol are independent from each other. A WorkInProgress driver was used with the UT-D09 cable like this:

 $ sigrok-cli --list-serial
 $ sigrok-cli -d uni-t-ut181a:conn=hid/cp2110/raw=/dev/hidraw0 --samples 10

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