SEN0641 RS485 PAR Sensor Reference: API & Pinout

This article delves into the Modbus-RTU communication protocol, explaining the data frame format, register addresses, and communication parameters essential for effective sensor data management.

Communication Protocol Description

1. Basic communication parameters

Interface	Encoding	Data bits	Parity bits	Stop bits	Error checking	Baud rate
RS485	8-bit binary	8	None	1	CRC	2400bit/s, 4800bit/s, 9600 bit/s configurable, default 4800bit/s

2. Data frame format definition

Using Modbus-RTU communication protocol, the format is as follows:

Initial structure ≥4 bytes of time

Address code = 1 byte

Function code = 1 byte

Data area = N bytes

Error check = 16-bit CRC code

End structure ≥4 bytes of time

Address code: The address of the sensor, which is unique in the communication network (factory default 0x01).

Function code: The function indication of the command sent by the host. This sensor reads the register function code 0x03 and writes the register function code 0x06

Data area: The data area is the specific communication data. Note that the high byte of 16-bit data is in front!

CRC code: A two-byte check code.

Host inquiry frame structure:

Address code	Function code	Register start address	Register length	Check code low bit	Check code high bit
1byte	1byte	2byte	2byte	1byte	1byte

Slave response frame structure:

Address code	Function code	Number of valid bytes	Data area 1	Data area 2	Nth data area	Check code
1byte	1byte	1byte	2byte	2byte	2byte	2byte

Register address

Register address	Content	Operation	Range and definition
0000H	Photosynthetically active radiation value	Read-only	True value
0052H	Deviation value	Read-write	Photosynthetically active radiation deviation value (16-bit signed)
07D0H	Device address	Read-write	1~254 (factory default 1)
07D1H	Device baud rate	Read-write	0 represents 2400, 1 represents 4800, 2 represents 9600

3. Communication protocol example and explanation

3.1 Read the current photosynthetically active radiation value

Inquiry frame: Read value function code 0x03

Address code	Function code	Register start address	Register length	Check code low bit	Check code high bit
0x01	0x03	0x00 0x00	0x00 0x01	0x84	0x0A

Response frame:

Address code	Function code	Return valid bytes	Solar radiation value	Check code low bit	Check code high bit
0x01	0x03	0x02	0x00 0x64	0x9B	0xAF

Photosynthetically active radiation value:

0064 (hexadecimal) = 100=> Photosynthetically active radiation value = 100μmol/㎡·s

3.2 Write deviation value

Inquiry frame: Write value function code 0x06

Address code	Function code	Register address	Modify value	Check code low position	Check code high position
0x01	0x06	0x00 0x52	0x00 0x0A	0xA8	0x1C

Response frame:

Address code	Function code	Register address	Modify value	Check code low position	Check code high position
0x01	0x06	0x00 0x52	0x00 0x0A	0xA8	0x1C

Write the current photosynthetically active radiation deviation value
000A (hexadecimal) =10=> photosynthetically active radiation deviation value = 10μmol/㎡·s, deviation value is 10μmol/㎡·s

3.3 modify the current address

Inquiry frame: (modify the current address to 0x02)

Address code	Function code	Register address	Modify value	Check code low position	Check code high position
0x01	0x06	0x07 0xD0	0x00 0x02	0x08	0x86

Response frame:

Address code	Function code	Register address	Modify value	Check code low position	Check code high position
0x01	0x06	0x07 0xD0	0x00 0x02	0x08	0x86

3.4 Modify the current baud rate

Inquiry frame: (Modify the current baud rate to 9600)

Address code	Function code	Register address	Modify value	Check code low bit	Check code high bit
0x01	0x06	0x07 0xD1	0x00 0x02	0x59	0x46

Response frame:

Address code	Function code	Register address	Modify value	Check code low bit	Check code high
0x01	0x06	0x07 0xD1	0x00 0x02	0x59	0x46

3.5 Query current address and baud rate

Inquiry frame:

Address code	Function code	Register address	Data length	Check code low	Check code high
0xFF	0x03	0x07 0xD0	0x00 0x02	0xD1	0x58

Response frame:

Address code	Function code	Return valid bytes	Address	Baud rate	Checksum low bit	Checksum high bit
0x01	0x03	0x04	0x00 0x01	0x00 0x01	0x6A	0x33

The real address of the device read is 01, and the baud rate is 0x01, that is, 4800.

Principle

The photosynthetically active radiation sensor uses the principle of photoelectric sensing and can measure the photosynthetically active radiation value in the spectral range of 400-700nm. The sensor uses high-precision photoelectric sensing elements, wide spectrum absorption, high absorption, and good stability; when there is light, it generates a voltage signal proportional to the intensity of the incident radiation, and its sensitivity is proportional to the cosine of the direct angle of the incident light.

Other Supplementary Information

Explanation of measurement units

umol/m²•s is the unit of photosynthetically active radiation. Photosynthetically active radiation refers to the radiation of effective light energy that plants can absorb and use during photosynthesis. Photosynthetically active radiation usually refers to light with a wavelength in the range of 400-700nm, which is the range of light required for plants to photosynthesize.
The umol in umol/m²•s stands for micromoles, a unit that describes the number of photons in the photosynthesis process. m² represents the area per square meter, and s represents the unit of time, i.e. seconds. Therefore, umol/m²•s represents the number of photons of photosynthetically active radiation per square meter per second.
The unit of photosynthetically active radiation, umol/m²•s, is often used to measure the intensity of photosynthesis and the growth status of plants. By measuring the number of photons of photosynthetically active radiation per square meter per second, the photosynthetic efficiency and photosynthetic rate of plant leaves can be evaluated, and a reference can be provided for plant growth, photosynthesis research, etc.