Table of Contents
4-Channel Temperature Input Module: MD-THRT4
The MD-THRT4, used with a PT100Ω temperature sensor, can measure temperatures between –100 and 500 ℃ with a precision of ±0.5%.
Specification
| Item | Description |
|---|---|
| Channels | 4 |
| Operating Temperature | -10 ~ 50 ℃ ((no condensation) |
| Operating Humidity | 35 ~ 85%RH |
| Sampling Rate | 200ms per channel |
| Input | RTD Sensor (PT100) |
| Allowable Line Resistance | 10Ω or less per line from the module to the temperature sensor |
| Precision | ±0.5% |
| Conversion Speed | 240ms per channel |
| Communication Method | RS-485 |
| Packet Transmission | 3ms |
| Isolation Method | No Isolation |
MD-THRT4’s Sampling Frequency
The sampling rate of the Temperature Input Module is 200ms per channel, and is constantly sampling the temperature sensor. Reading the temperature returns the most recently sampled value.
The Temperature Input Module samples all channels at once, so at 200ms per channel, the total sampling time for four channels is 800ms. Therefore, there is no benefit in reading at a rate greater than 800ms, as it will always return the same value.
When the system is first powered on, all four channels are scanned once. Reading at this time will return an invalid value. Please allow at least 800ms from the time the system is powered on before reading from the module.
Return Value
The return value is the temperature in °C multiplied by 10. In other words if the module returns the value 205, the actual temperature is 20.5 °C.
If an error occurs, the following values may be returned.
| Value | Description |
|---|---|
| 20001 ~ 20003 | An error occurred while transmitting the value to the CPU |
| 20004 | Invalid module ID |
| 20005 | Sensor is not connected |
| 55555 | Value exceeds valid maximum (500.0 °C) |
| 11111 | Value is below valid minimum (-100.0 °C) |
Modbus Starting Address
Each module has 4 channels, each with its own unique Modbus address.
| Channel | 0 | 1 | 2 | 3 |
|---|---|---|---|---|
| Starting Address(base 10) | 300 | 301 | 302 | 303 |
| Starting Address(base 16) | 12C | 12D | 12E | 12F |
| Address (base 10) used by HMI (SCADA) | 40301 | 40302 | 40303 | 40304 |
Module ID (Modbus Slave Address) Assignment
On the front of the module, there is a rotary switch labeled ID, that is used to select the Modbus slave address for the module. When installing multiple modules of the same type, the ID for each module should be unique.
Rotary switch position 0 corresponds to Modbus slave address 10. If the ID is changed after the module is powered on, it must be power cycled for the new ID to take effect.