SR05-D1A3-PV manual v1801 54/83
6.6 Network communication: example master request to SR05
Normal sensor operation consists of requesting the output of registers 0x1002 + 0x1003;
the temperature compensated solar radiation. For quality assurance also the sensor
serial number, register 0x1028 and the temperature in register 0x1006, are useful.
In this example a SR05-D1A3-PV has address 64. The example requests the solar
radiation (temperature compensated) register 0x1002 + 0x1003, sensor serial number,
register 0x1028, and the temperature of the instrument register 0x1006. The values are
represented in hexadecimals.
Note: 32 bit data are represented in 2 registers. MSW and LSW should be read together
in one request.
Request for solar radiation, register 2 + 3:
Master Request:
0x40 0x03 0x1000 0x0004 0x4FD8
0x40 = Modbus slave address, decimal equivalent = 64
0x03 = Modbus function code: 0x03 Read holding registers
0x1000 = Starting register, the master requests data starting from register
0x1000.
0x0004 = Length, the number of registers the master wants to read. 4 registers
0x4FD8 = CRC, the checksum of the transmitted data
Sensor response:
0x40 0x03 0x08 0x0040 0x0005 0x0001 0x7C4F 0x79DA
0x40 = Modbus slave address, decimal equivalent = 64
0x03 = Modbus function
0x08 = Number of bytes returned by the sensor. 8 bytes transmitted by the sensor
0x0040 = Register 0x1000; Modbus address
0x0005 = Register 0x1001; Serial settings, 19200 baud, 8 data bits, even parity
bit, 1 stop bit
0x0001 = Register 0x1002; Temperature compensated signal, Most Significant
Word (MSW). Decimal equivalent = 1
0x7C4F = Register 0x1003; Temperature compensated signal, Least Significant
Word (LSW) = Decimal equivalent = 31823
0x79DA = CRC, the checksum of the transmitted data
Together, register 0x1002 and 0x1003 are representing the temperature
compensated solar radiation output measured by the SR05-D1A3-PV. The MSW is
in register 0x1002 and the LSW in 0x1003. The output has to be calculated by the
formula: ((MSW x 2
16
) + LSW)/100. In this example the result is: ((2
16
x 1) +
31823)/100 = 973.59 W/m²
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