Modbus¶
The probe can be addressed directly using the MODBUS RTU protocol, to request the measured CO2 values. The parameters highlighted in yellow should be selected according to the table below.
Baud rate: 19’200 8N1
| Important: In order to communicate directly with the digital probe via MODBUS, please use the E2-05XX-MOD cable. The digital MODBUS protocol is delivered over RS485. |
|---|
Request¶
| Probe address | Command ID | Start address of device data | Number of records | MODBUS CRC | ||
|---|---|---|---|---|---|---|
| 0x01 | 0x04 | 0x00 | 0x00 | 0x00 | 0x00 | 0x0000 |
Probe address
0…255, default at ‘1’
- Device data:
| Start Address | Data Bytes | |
|---|---|---|
| 0x00 Quantity <=3 |
Serial No. [3] | [3] |
| Serial No. [2] | [2] | |
| 0x01 Quantity <= 2 |
Serial No. [1] | [1] |
| Serial No. [0] | [0] | |
| 0x02 Quantity 1 |
Diff. Pressure [1] | [1] |
| Diff. Pressure [0] | [0] |
-
CRC: CRC 16bit (MODBUS)
-
Example request (hexadecimal): 01 04 00 00 00 03 B0 0B
01 > Probe address
04 > Command ID
00 > not used
00 > start address of device data
00 > not used
03 > number of data
B0 > CRC 16bit Modbus (LSB)
0B > CRC 16bit Modbus (MSB)
Response¶
| 0x01 | 0x04 | 0x00 | 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 | 0x00, 0x00 |
|---|---|---|---|---|
-
Serial number: 4 byte int32
-
Differential pressure: 2 byte int16
| Range of the probe | +/-25, +/-50, +/-100, +/-250 Pa | +/-500 Pa |
|---|---|---|
| Differential pressure value > positive range | = value / 100 | = value / 50 |
| Differential pressure value > negative range | = -1 x ((65535 - value + 1) / 100) | = -1 x ((65535 - value + 1) / 50) |
Indication:
If the value of the differential pressure data > 0x7FFF > Differential pressure is neg.
If the value of the differential pressure data <= 0x7FFF > Differential pressure is positive.
- Example response (hexadecimal) to the request above: 01 04 06 00 7A 73 F0 07 D0 A0 42
01 > Probe address
04 > Command ID
06 > number of data [bytes]
00 > serial number [byte 3] (MSB)
7A > serial number [byte 2]
73 > serial number [byte 1]
F0 > serial number [byte 0] (LSB)
07 > differential pressure [byte 1]
D0 > differential pressure [byte 0]
A0 > CRC 16bit Modbus (LSB)
42 > CRC 16bit Modbus (MSB)
Serial number of the example: 0x00 7A 73 F0 > 8025072
Differential pressure of the example: 0x07 D0 > 2000 > +20 Pa (range of probe is e. g. +/-50 Pa)
Connection timeout: When TCP connection is open and for more than 30 seconds no communication is performed, the device automatically closes the TCP connection. In case of a communication interruption, this prevents the socket being blocked.
Additional MODBUS details can be found here: MODBUS in RMS.