TMT85 Temperature Transmitter Wiring Overview
The TMT85 is a modular temperature transmitter that supports thermocouple and RTD inputs. Correct wiring is the foundation for ensuring measurement accuracy and stable operation. This article introduces its terminal connection methods by type.
Thermocouple Wiring Method
The thermocouple signal is a millivolt-level voltage and must be connected directly to the corresponding terminals of the transmitter.
- Positive: Connect to terminal 5 (+)
- Negative: Connect to terminal 6 (-)
Note that the polarity must not be reversed, otherwise the measured value will drift in the opposite direction.
RTD Wiring Method
RTDs are classified into 2-wire, 3-wire, and 4-wire types based on the number of lead wires. The wiring methods differ, and the accuracy increases accordingly.
2-Wire RTD
- One end connects to terminal 6
- The other end connects to terminal 6 (or according to the transmitter definition, usually terminals 5 and 6 are shorted and then connected to the RTD)
Note: The original description states "one end connects to a terminal, the other end connects to terminal 6." This is organized here according to the conventional 2-wire connection method. Please refer to the transmitter manual for actual practice.
3-Wire RTD
- The single lead end connects to terminal 4
- The two lead ends connect to terminal 5 and terminal 6 respectively
The 3-wire configuration can partially compensate for lead resistance and is suitable for medium-accuracy applications.
4-Wire RTD
- One pair of leads connects to terminal 3 and terminal 4
- The other pair of leads connects to terminal 5 and terminal 6
The 4-wire configuration completely eliminates the effect of lead resistance and is used for high-precision measurements.
Wiring Method Comparison and Selection Recommendations
| Sensor Type | Terminal Connection | Accuracy | Application Scenario |
|---|---|---|---|
| Thermocouple | 5(+) / 6(-) | Medium | High-temperature measurement |
| 2-Wire RTD | 6 and 6 (or 5-6 shorted) | Low | Short distance, low cost |
| 3-Wire RTD | 4 / 5 / 6 | High | Standard industrial |
| 4-Wire RTD | 3 / 4 / 5 / 6 | High | Laboratory, high precision |
Wiring Precautions
- Be sure to disconnect power before wiring to avoid damaging the transmitter.
- Use shielded cables, with the shield grounded at one end.
- Ensure terminal screws are tightened, and contact resistance is as small as possible.
- For RTDs, use 3-wire or 4-wire configurations whenever possible to minimize errors.
Following the above methods ensures stable and reliable operation of the TMT85 temperature transmitter.