UNI-T UT81B
This is my small personal review ot this meter.
UT81B is declared as a kind of scopemeter - it is a multimeter with some basic oscilloscope functions. It can be either battery powered or it has also 6V/450mA DC adapter. It has opticaly sealed USB transfer, can measure DC V up to 1000V, AC up to 750V, resistance up to 40MOhm, frequency up to 10MHz (probably sinus), bandwidth for UT81B is "only" 8MHz (UT81A only 2MHz - thats probably the difference) with 40MS/s giving resolution 100ns/div - 5s/div with 8bit ADC, capacitance 100uF, AC/DC current 10A. Of course it has also a diode and continuity test. Inacurracy is overall around 1%. That's what documentation says.
Few words about meter and it's usage:
- Its software is not fast, neither too slow - acceptable, but could be faster.
- 4xAA batterie included (Eastpower) lasted only few hours of usage, with 1.38V each the indicator was showing low power.
- Documentation is describing obvious things and contains a lot of words of warning that you do not have to try to shave with the meter.. you know. Not much of help., but it's printout is of good quality for "Made in China". I am missing e.g. the information on how meter behaves when there are batteries but you connect DC adaptor. IMHO it will deplete the batteries down to adaptor level as adaptors is giving 5.8+V, but a new alkaline batteries up to 6.32V. Will see how long new Energiser batteries will go.
- The autoranging is bit confusing but as you touch the range button it will let you choose. So far good.
- Data that you save in meter you can recall even after you switch off and remove batteries.
- Most troubles I had with trigger functionality. The bad thing here is that if you select one shot measurment, whenever meter goes to hold mode, you can not change anything on the screen until you unhold, while immediately triggering makes you lost. You have to switch to "auto" mode, then you can change the ranges, time base etc. again.
- The worst thing on the meter so far for me is, that it is leaking 50Hz (European 230V/50Hz mains) from the AC/DC adaptor up to 1-2Vef. That's really terrible. I have to find some solution for that.
- Meter is in the reality more thick than what it seems to look from pictures. It is quite a brick, while making a solid feeling. The most of the bottom is of course occupied by batteries.
- From my feeling the meter is meant mainly for measuring of larger signals. It is hard to measure very small signals on let's say higher DC voltage as meter can shift the 0 down or up only 4divs - means eg. signal 10mVpp on the 4V you can measure on 1V resolution lowest. If you switch to 500mV your signal is out of the scope. Also the 50Hz leakage is making impossible to measure small signals even on batteries I still get lot of 50Hz noise.
- Attached probes are good, but I did not found a way how to disassemble them. If you cut or damage the wire, you're done and have to buy a new probes. Crocodiles are quite big with lot of force, which is not suitable for sensitive components - that's probably because they are rated 1000V, but it is nice they are easily attachable to normal probes.
- Attached CD contains software for all UNI-T meters, but of course only for Windows.
This is Linux identificaton:
usb 2-8: new full speed USB device using ohci_hcd and address 3 usb 2-8: New USB device found, idVendor=1a86, idProduct=e008 usb 2-8: New USB device strings: Mfr=1, Product=2, SerialNumber=0 usb 2-8: Product: USB to Serial usb 2-8: Manufacturer: WCH.CN generic-usb 0003:1A86:E008.0002: hiddev96,hidraw1: USB HID v1.00 Device [WCH.CN USB to Serial] on usb-0000:00:02.0-8/input0
It looks the USB is in general only USB to serial port converter.
I've got a description of communication protocol from UNI-T. It confirms this is only serial port. Here is the description of UT81B protocol.