Hach LDO AQS sensors, User Manual, Page: 8 / 60

Operation
Modbus registers
Use the Modbus registers in the control system to configure and get data from the sensor. Refer to
Table 2 . Set the communication parameters to RTU (Zf), 19.2 Kpbs, 8 bits, no parity and 1 stop bit.
The data type for all registers in Table 2 is unsigned integer.
Table 2 Modbus registers
Register Name Description Minimum/maximum Length
(bytes) Access
40001 Dissolved oxygen mg/L O
2
× 1000 (e.g.,
8.082 mg/L O
2
shows as
"8082")
–5/21 2 Read
40002 Temperature
(Celsius) °C × 100 (e.g., 26.41 °C shows
as "2641")
0/50 2 Read
40003 Software version Version × 100 (e.g.,
4.56 shows as "456")
0/100 2 Read
40004 Sensor cap lot
number Year and day (e.g., 2015, day
136 shows as "15136")
0/65535 2 Read
40005 Serial number Hexadecimal number from
ASCII code
(e.g., Registers
40005–40010 are "3133",
"3132", "3330", "3030", "3030",
"3937", in ASCII code "13",
"12", "30", "00", "00", "97",
combined shows as
"131230000097")
— 12 Read
40012 Percent
saturation (%) Dissolved oxygen as %
saturation 0/200 2 Read
40013 Altitude (meters) Altitude in meters (default:
0 meters) 0/5000 2 Read/Write
40014 Salinity (PSU) Salinity in PSU (default: 0 PSU) 0/250 2 Read/Write
49998 Sensor address Sensor address (default: 247) 1/99 2 Read/Write
Configure the sensor
Use the Modbus registers to enter the altitude and salinity values for the sample.
1. Enter the altitude in meters at the location where the sensor is installed (default: 0 meters).
2. Enter the salinity value of the sample in PSU (practical salinity units). Use the steps that follow to
get the salinity value.
a. Use a conductivity meter to measure the conductivity of the sample in mS/cm at a reference
temperature of 20 °C (68 °F).
b. Find the salinity value in PSU from Table 3 .
Table 3 Salinity (PSU) per conductivity value (mS/cm)
mS/cm PSU mS/cm PSU mS/cm PSU mS/cm PSU
5 3 16 10 27 18 38 27
6 4 17 11 28 19 39 28
7 4 18 12 29 20 40 29
8 English