Water EC/TDS Sensor with Modbus communication

In this guide, we will walk through the process of connecting and reading data from a Water EC/TDS sensor from CWT CO., LIMITED.

This transmitter features online calibration, automatic temperature compensation, over-current and overvoltage protection, and standard industrial signal outputs. We will use Modbus communication to interface with the transmitter and extract sensor readings.

Materials Needed

• Water EC/TDS transmitter (CWT CO., LIMITED)- Used CWT-BL-EC-4400-S
• ESP32
• MAX485 module for RS485 communication
• Power supply (14V for optimal performance)
• Connecting wires

Specifications

The EC/TDS transmitter supports various output signals including 0–5V, 0–10V, 4–20mA, and RS485 (Modbus RTU). For this guide, we will focus on using the RS485 output.

Wiring the Transmitter

Arduino Code for Modbus Communication

#include <ModbusMaster.h>

#define RXD2 16
#define TXD2 17

#define MAX485_DE      32
#define MAX485_RE_NEG  33

ModbusMaster node;

void preTransmission() {
  digitalWrite(MAX485_RE_NEG, 1);
  digitalWrite(MAX485_DE, 1);
}

void postTransmission() {
  digitalWrite(MAX485_RE_NEG, 0);
  digitalWrite(MAX485_DE, 0);
}

void setup() {
  Serial.begin(9600); 

  pinMode(MAX485_RE_NEG, OUTPUT);
  pinMode(MAX485_DE, OUTPUT);
  digitalWrite(MAX485_RE_NEG, 0);
  digitalWrite(MAX485_DE, 0);

  Serial2.begin(9600, SERIAL_8N1, RXD2, TXD2);
  node.begin(0, Serial2); 
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);
}

void loop() {
 
  uint8_t result = node.readHoldingRegisters(0x00, 2); // Request 2 registers starting from address 04

  if (result == node.ku8MBSuccess) {
    uint16_t calibrationValues = node.getResponseBuffer(0); // First register: Calibration values
    uint16_t sensorReadings = node.getResponseBuffer(1);    // Second register: Sensor readings
    
    Serial.print("Calibration Values: ");
    Serial.println(calibrationValues);
    Serial.print("Sensor Readings: ");
    Serial.println(sensorReadings);
  } else {
    Serial.print("Error reading registers: ");
    Serial.println(result, HEX);
  }

  delay(2000); // Delay before the next read
}

Identifying the Correct Slave ID

The default slave ID for the transmitter is 1, as specified in the datasheet.

If you encounter issues with communication, it is crucial to verify the slave ID. Here’s a method to identify the correct slave ID,

RS485 Sensor Selection and Initial Checking Using Software application

Note: Although the transmitter is rated for 12–24V, it was found that supplying 14V ensures proper functionality. Ensure your power supply can provide a stable 14V to avoid any issues.

Detailed Code Explanation

Modbus Registers

The datasheet can be accessed through the link.

The register at address 0x00 (40001 in decimal) holds the calibration solution value, and the register at 0x01 (40002 in decimal) holds the EC/TDS value.

We request two registers to get both calibration value and EC/TDS Values.

uint8_t result = node.readHoldingRegisters(0x00, 2);

Final Calculations can be done according to,

Conclusion

By following this guide, you should be able to successfully connect and read data from the Water EC/TDS transmitter using Modbus communication.

This setup allows for real-time monitoring of EC/TDS levels in various industrial applications.

Contact us for any consultations or projects related to any RS485 sensor.

Protonest for more details.

Protonest specializes in transforming IoT ideas into reality. We offer prototyping services from concept to completion. Our commitment ensures that your visionary IoT concepts become tangible, innovative, and advanced prototypes.

Our Website: https://www.protonest.co/

Email: udara@protonest.co

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