SIGNUX COA01

The SX-COA01 is an integrated conductivity transmitter for aqueous solutions. Electrode, temperature sensor and electronics share one body, so the probe connects directly to an RS485 bus with Modbus RTU protocol and reports conductivity, temperature, salinity and total dissolved solids.

Temperature compensation is automatic: the conductivity read is referred to a reference temperature (25 °C by default) with an adjustable coefficient. Two cell constants are available, k = 1 for 1-2000 µS/cm and k = 10 for 10-20000 µS/cm.

Typical applications: surface water quality, aquaculture, wastewater treatment, environmental monitoring, pharmaceutical and food processes, drinking water.

• •Conductivity up to 20000 µS/cm; temperature -20 to +60 °C with 0.1 °C resolution
• •One-piece design, light and simple, easy to install
• •IP68 protection rating, pressure-rated to 0.6 MPa
• •Salinity and TDS conversion on board
• •RS485 interface with Modbus RTU protocol, easy to connect to a PLC, datalogger or computer
• •Configurable Modbus address and baud rate
• •Wide supply voltage range: 7-30 V DC

Specifications

The probe is supplied with a four-core cable with bare ends.

The order code states the cell constant. It cannot be changed afterwards: choose it from the conductivity to be measured.

• •One integrated conductivity transmitter
• •5 m cable (or the length ordered)

• •Submerged installation: run the cable through a rigid waterproof pipe and screw the pipe onto the upper NPT 3/4" thread of the probe, sealing the thread with PTFE tape. The top of the probe and the cable must stay dry.
• •Pipe installation: screw the probe into the pipe or tee through its NPT 3/4" thread.
• •Keep the electrode fully immersed and away from air bubbles. Do not exceed 0.6 MPa or 60 °C.
• •Wire A to A and B to B; swapped wires are the most common cause of a probe that does not answer.

• •The probe needs no routine maintenance. If it fails, do not open it: contact SIGNUX.
• •An electrode that has been stored dry must be soaked in distilled water for several hours before use, to reactivate it. An electrode in frequent use may be stored in distilled water.
• •Cleaning: organic deposits come off with warm water and detergent, or with alcohol. Calcium and magnesium scale is best removed with 10 % citric acid. Clean the electrode poles only chemically or by shaking them in water: wiping them destroys the platinum black coating.
• •Calibrate before each campaign of use and, in continuous use, every three months. Adjust the frequency to the fouling and chemical deposits of the application.

Calibration is done over RS485, from the SIGNUX tool or from any Modbus master, with registers 0x0110 and 0x0111 written together with function code 16.

Rinse the electrode, immerse it in a standard solution of known conductivity, shake it gently to speed up the response and let it settle. When the reading is stable, write 0x0004 to register 0x0110 and the conductivity of the standard to register 0x0111, multiplied by 10 for the k = 1 probe (1-2000 µS/cm) or as it is for the k = 10 probe (10-20000 µS/cm). Example 3 in the Modbus chapter shows the exact frame.

Two related settings can also be adjusted: the temperature compensation coefficient (registers 0x0052-0x0053, 0.02 by default) for solutions with a different temperature coefficient, and the cell constant (registers 0x0054-0x0055). Both are 32-bit floating-point values, high word first. Small corrections to the reading can be made with the offsets in 0x0050 (temperature) and 0x0051 (conductivity).

All 16-bit values are sent high byte first. The 32-bit floating-point registers (compensation coefficient and cell constant) are big-endian: high word in the lower address.

• UINT16: 16-bit unsigned integer
• INT16: 16-bit signed integer

send frame：

Master request: 01 03 0000 0002 C4 0B

Response frame: (For example, a device with a range of 0~2000μs/cm reads a conductivity value of 1000μs/cm and a temperature of 26.5°C)

Slave response: 01 03 04 2710 0109 30 D4

• Conductivity calculation: 2710 (hex) = 10000 => Conductivity = 1000.0 μs/cm
• Temperature calculation: 109H (hexadecimal)=265=>temperature=26.5℃

Perform numerical correction on the deviation value of the current conductivity value setting of the device whose address is 01

Sending frame: (if the current range is 0~2000μs/cm, the output conductivity value is 990, tocorrect the value to 1000, the difference is 1000-990=10, and the expansion is 10 times to100=>64H (ten Hexadecimal), the register content is written 00 64)

Master request: 01 06 0050 0064 88 30

Response frame: (according to the MODBUS standard, the response is a mirrored message of the delivered frame)

Slave response: 01 06 0050 0064 88 30

Use the standard solution of 1413μs/ms to calibrate the device with the address 01ranging from 1 to 2000

Sending frame: write 00 04 to 0110H and 0111H respectively, and convert 1413*10 intohexadecimal to 37 32

Master request: 01 10 0110 0002 04 00043732 29 17

Response frame: (according to the MODBUS standard, the response is a mirrored message of the delivered frame)

Slave response: 01 10 0120 0002 41 fe |||