lamaPLC: PTA8C04 4-channel PT100 Modbus Modul

PTA8C04 is a specific model of 4-Channel PT100 RTD Temperature Sensor Module that uses RS485 communication for industrial monitoring, enabling it to read temperatures from multiple PT100 resistance temperature detectors (RTDs) and transmit data via the Modbus RTU protocol for PLCs and other controllers, often mounted on DIN rails.

• Operating Temperature: -40 to 85°C
• Working Voltage: DC 12V/24V
• Working Current: 14-18 mA
• Compatible Sensor: PT100 3-wire or 2-wire
• PT100 Sensor Range: Version A -40℃ to +220℃, Version B -40℃ to +500℃
• Temperature Measurement Accuracy: 1%
• DIN Rail: PCB board width UM72 (72mm) for DIN35 / C45 rail

Default settings: SlaveID: 1, 9600 baud, parity: N,8,1

The PTA8C04 is a 4-channel PT100 RTD acquisition module that communicates via RS485 Modbus RTU, which is fundamentally different from the SPI-based MAX31865. To use it with an Arduino, you typically need an RS485 to TTL converter (like a MAX485 module) and a Modbus library.

Hardware Connections

Connect your Arduino to the PTA8C04 through an RS485 converter:

• VCC/GND: 12V–24V DC to PTA8C04; 5V/GND to RS485 converter.
• A/B Pins: Connect A to A and B to B between the PTA8C04 and the RS485 converter.
• RO (Receive): Arduino Pin 2 (if using SoftwareSerial).
• DI (Driver Input): Arduino Pin 3.
• DE/RE (Enable): Arduino Pins 4 & 5 (tied together to control direction).

Arduino Example Code

This code uses the ModbusMaster library to read temperatures from the first two channels.

#include <ModbusMaster.h>
#include <SoftwareSerial.h>
 
#define MAX485_RE_DE 4  // Pins for RE and DE
SoftwareSerial rs485(2, 3); // RX, TX
 
ModbusMaster node;
 
void preTransmission() { digitalWrite(MAX485_RE_DE, 1); }
void postTransmission() { digitalWrite(MAX485_RE_DE, 0); }
 
void setup() {
  pinMode(MAX485_RE_DE, OUTPUT);
  digitalWrite(MAX485_RE_DE, 0); // Start in receive mode
 
  Serial.begin(9600);
  rs485.begin(9600); // PTA8C04 default baud is 9600
 
  node.begin(1, rs485); // Default slave ID is 1
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);
}
 
void loop() {
  // Read 4 registers starting at 0x0000 (Channels 1-4)
  uint8_t result = node.readHoldingRegisters(0x0000, 4);
 
  if (result == node.ku8MBSuccess) {
    for (int i = 0; i < 4; i++) {
      int16_t rawTemp = node.getResponseBuffer(i);
      // PTA8C04 provides temperature x10. Divide by 10.0 for Celsius
      float celsius = rawTemp / 10.0;
      Serial.print("CH"); Serial.print(i+1);
      Serial.print(": "); Serial.print(celsius); Serial.println(" C");
    }
  } else {
    Serial.print("Modbus Error: "); Serial.println(result, HEX);
  }
  delay(2000);
}

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