Hardware Overview > Sensors and Probes > PCD-S

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:

Device Data		Byte
Start Address	Data Bytes
0x00 Quantity <=3	Serial No. [3]	[3]
0x00 Quantity <=3	Serial No. [2]	[2]
0x01 Quantity <= 2	Serial No. [1]	[1]
0x01 Quantity <= 2	Serial No. [0]	[0]
0x02 Quantity 1	Diff. Pressure [1]	[1]
0x02 Quantity 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

Probe address	Command ID	Number of data bytes	Data (4…10 bytes)	CRC 16 bit MODBUS
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.