Table of Contents
ML-THRT1
The PT100Ω is a temperature sensor widely used in the industrial field because it can measure a wide range of temperatures from -100 to +500 degrees Celsius. The ML-THRT1 module converts the resistance value of the PT100Ω sensor to a digital temperature value. Simply read the digital value via Modbus RTU over RS-485.
Specifications
| Input Power | 5VDC |
|---|---|
| Temperature Sensor | RTD (PT100Ω / 3-Wire) |
| Measurement Range | -100 ~ 500 ℃ |
| Precision | ±0.5% |
| Operating Temperature | -10 ~ 60 ℃ |
| Operating Humidity | 35 ~ 85%RH |
| Sampling Period | 200ms |
| Allowable Sensor Wire Resistance | Not more than 10Ω per wire, but each wire should have the same resistance. |
| Communication Method | RS-485 Modbus RTU 57600bps, 8 bits, 1 stop bit, no parity (Fixed, cannot be changed) |
| Packet Transfer Speed | 3ms |
| Electrical Isolation | None |
Connections
A termination resistor may be necessary if a ML-THRT1 is the last node in an RS-485 network.
Data Format
The ML-THRT1 returns the digital temperature multiplied by 10 in 2 bytes. For example, a value of 20.5°C will be returned as 205 (0x00DC). Negative values have the most significant bit set to 1. For example, a value of -20.5°C will be returned as 32988 (0X80DC). For negative values, subtract 32768 to obtain the absolute value.
- If the temperature read is greater than 500°C, the value 5555 is returned.
- If the temperature read is lower than -100°C, the value -1111 is returned.
- If the sensor is not connected, the value 8888 is returned.
Modbus Communication Protocol
The Modbus slave address can be set using the rotary dial (0 ~ 10) on the side the ML-THRT1.
To read the digital temperature value, send a Modbus query with Function code 3 and data length 1 to start address 400 (0x0190).
MOACON Example
The following example illustrates how to use the ML-THRT1 with the MOACON.
#include "moacon500.h" void cmain(void) { openCom(0, 57600, com8N1); comPower(1); int Temp; char res; while(1) { res = RTU_readRegs(0, 1, &Temp, 400, 1); if(res == -1) { printf("Temp = %d", Temp); } else { printf("Temp = Error"); } delay(1000); } }
