A-37
MODEL 2700 APPENDIX A
MODBUS PROTOCOL
measurement unit of measure
Conductivity S/cm
Dissolved solids ppm-TDS
Dual Difference S/cm
Dual Ratio none
Dual %Pass, %Reject %
ORP mV
pH pH
Resistivity ohm-cm
Temperature °C
Example: Read Primary measurement of Sensor1
Sensor_number = 1
First Register = 51 + 4*(Sensor_number - 1) = 51
Second Register = 52 + 4*(Sensor_number - 1) = 52
Function Code 04 Read Input Registers
Starting Address 51
Number of Points 02
Register contents in hexadecimal
30051: A836H
30052: 8125H
sign = quotient(36H/80H)
=0
exponent = 2*remainder(36H/80H) + quotient(A8H/80H)
= 2*36H + 1
= 2*54 + 1
= 109
mantissa = [10000H*remainder(A8H/80H) + 100H*(25H) + 81H] / 2^23
= [10000H*28H + 100H*25H + 81H] / 2^23
= 282581H / 2^23
= .3136445
= [65536*40 + 256*37 + 129] / 2^23
= 2631041 / 8388608
= .3136445
measurement value = (-1)^sign * 2^(exponent-127) * 1.mantissa
= (-1)^0 * 2^(109-127) * 1.3136445
= 1 * 2^-18 * 1.3136445
= 5.011 * 10^-6
measurement value = 5.011 * 10^-6 S/cm
= 5.011 µS/cm
Conductivity 5.011 µS/cm
Measurements in Integer format 1-17
Measurements are the Primary and Secondary sensor measurements, or a Dual measurement.
Sensor Primary measurement
Register = 1 + 2*(Sensor_number - 1)
Sensor Secondary measurement
Register = 2 + 2*(Sensor_number - 1)
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