A small utility to read data from the inexpensive table multimeter UNI-T UT803 via the RS232 port.
The program can be used stand-alone to record data from the multimeter as CSV files. See the following help-listing for more information.
$ python ut803.py --help
usage: ut803.py [-h] [-d DELAY] [-m] port output
Record and monitor data from a UNI-T UT803 table multimeter via serial
connection. Either connect the UT803 via the RS-232 port, or USB. In the
second case, a virtual RS-232 device is created.
positional arguments:
port Serial port for UT803 connection.
output Specify output file. Use - for stdout.
optional arguments:
-h, --help show this help message and exit
-d DELAY, --delay DELAY
Delay measurement for specified number of seconds.
-m, --monitor Display a line with the current value and device
status.
Please have a look inside the file. There is a class called UT803 and it is rather simple to use. Too lazy to document that at this time of the night.
Aside from the actual transmission, the real (non-USB) RS232 port of the multimeter requires power supply via DTR and RTS signals from the PC.
Each measurement is sent as a 11 byte packet, forming a fixed length 9 ASCII character line, terminated by CR+LF. The charaters have the following meanings
| Byte Position | Interpretation |
|---|---|
| 0 | Exponent |
| 1-4 | Base Value |
| 5 | Measurement Type |
| 6-8 | Flags |
The flags and the measurement are encoded in a "super-decimal" format, possibly hex-ish. Anyway, the numericals are 0123456789:;<=>?. The characters are consecutive in the ASCII table, so the value of the super-decimal characters can be determined by subtracting 48 from their ASCII value.
| Char | Numerical Value | ASCII Code |
|---|---|---|
| : | 10 | 58 |
| ; | 11 | 59 |
| < | 12 | 60 |
| = | 13 | 61 |
| 14 | 62 ? | 15 | 63
The numerical value of the measurement is encoded with a base value in byte 1-4 and an exponent value in byte 0. To get to the actual (base) unit with the exponent, you might have to add an offset to the exponent.
value = int(b[1-4]) * 10**(exponent - offset)
For example, the current in the µA setting is measured in units of tenths of µA, so to get the current in µA, you have to subtract one from the exponent. The following table summarizes the exponent offsets and lists the corresponding target units.
| Measurement Setting | Offset | Unit | Note |
|---|---|---|---|
| Voltage | 3 | V | exponent & 0x4 == 0 |
| Voltage | 5 | V | exponent & 0x4 > 0 |
| Current A | 2 | A | |
| Current mA | 2 | A | |
| Current µA | 1 | A | |
| Resistance | 1 | Ω | |
| Continuity | 1 | Ω | |
| Capacitance | 12 | F | |
| Diode Test | 0 | V | |
| Frequency | 0 | Hz | |
| Temperature | 0 | °F / °C | |
| hFE | 0 |
Another special case is the third exponent-bit for voltage measurements. If it is set, the displayed voltage on the multimeter is given in mV, therefore the exponent is different. Who came up with this sh#t?!
A straight forward table. There are some missing entries, maybe the controller support additional modes, but I don't know. The UT803 only sends these.
| Code | Measurement Type | Base Unit |
|---|---|---|
| 1 | Diode Test | V |
| 2 | Frequency | Hz |
| 3 | Resistance | Ohm |
| 4 | Temperature | °F/°C, depending on FLAG_2_3 |
| 5 | Continuity | ? |
| 6 | Capacitance | nF |
| 9 | Current | A |
| ; | Voltage | V |
| = | Current | µA |
| hFE | ? | Current | mA
There are three flag characters encoding 4 bits each. The first char encodes interpretation hints of the value. The second char specifies the recording mode. Last but not least, the last char specifies range and AC/DC options.
| Byte | Bit | Designation | Interpretation |
|---|---|---|---|
| 1 | 1 | FLAG_1_1 | Set on Overload condition. |
| 1 | 2 | FLAG_1_2 | unused |
| 1 | 3 | FLAG_1_3 | Set if value is negative. |
| 1 | 4 | FLAG_1_4 | Always set except when unit is °F. |
| 2 | 1 | FLAG_2_1 | unused |
| 2 | 2 | FLAG_2_2 | Record minimum value |
| 2 | 3 | FLAG_2_3 | Record maximum value |
| 2 | 4 | FLAG_2_4 | Hold value |
| 3 | 1 | FLAG_3_1 | unused |
| 3 | 2 | FLAG_3_2 | Auto-Range mode |
| 3 | 3 | FLAG_3_3 | AC TrueRMS measurement |
| 3 | 4 | FLAG_3_4 | DC measurement |
Copyright (C) 2016 Gregor Vollmer mail@dynamic-noise.net
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.