User manual for - TEMPERATURE TRANSDUCER TRS-02a
6.2.
READING OF THE MEASUREMENT RESULT
Averaged (filtered) result of temperature measurements is available in holding register
no. 01h. Reading of the result may be done using MODBUS RTU function 03h. If single
holding register is being readed (01h), then module signalises any alarm situation by
exception code (different than standard answer frame – see example 1). If group of holding
registers (contain status register 02h) or only status register (02h) is being readed, then device
transmits standard answer with current measurement status.
6.3.
TRANSMISSION ERRORS DESCRIPTION
If an error occurs while write or read of single register, then the device sends an error
code according to Modbus RTU specifications (example message no 1).
Error codes:
00h
- measurement correct (this error code can be readed from status registers only),
01h
- illegal function (only functions 03h and 06h are available),
02h
- illegal register address
03h
- illegal data value
10h
- water inside module,
20h
- temperature sensor damaged,
40h
- exceed of lower border of input range ( -50°C, sensor damage possible),
80h
- exceed of upper border of input range (550°C, sensor damage possible),
A0h
- PT-100 line broken/opened,
60h
- PT-100 line short circuit
10h, 20h, 40h, 60h, 80h, and A0h codes can appear only during reg. 01h is reading by 03h
function (read of a single register).
Error code can be a logical sum of two or more errors. Sensor failure usually do not
breaks actualisation of measurement results, and current result can be readed
using multi register mode ( in single register mode the modules send off the
exception codes).
6.4.
EXAMPLES OF QUERY/ANSWER FRAMES
Examples apply for device with address 1. All values are represent hexadecimal.
Field description:
ADDR
Device address on Modbus network
FUNC
Function code
REG H,L
Starting address (address of first register to read/write, Hi and Lo byte)
COUNT H,L
No. of registers to read/write (Hi and Lo byte)
BYTE C
Data byte count in answer frame
DATA H,L
Data byte (Hi and Lo byte)
CRC L,H
CRC
error check (Hi and Lo byte)
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