RTDs (Resistance Temperature Detectors) are sensors that measure temperature changes by detecting resistance changes in a material. Among the most widely used RTDs is the PT100, which is a platinum-based resistance sensor. It is notable for its accuracy, stability, and repeatability. However, wiring a PT100 can be challenging, especially if you are new to it.
This article aims to provide a comprehensive guide on wiring a duplex RTD PT100. It will cover the basics, such as what PT100 is and how it works, as well as the wiring diagram and frequently asked questions.
What is a PT100?
A PT100 is an RTD that is primarily made of platinum (99.99%), which is a material with a high resistance to temperature. It has a positive temperature coefficient, which means that its resistance increases linearly with temperature. This characteristic makes PT100 sensors ideal for a wide range of applications, especially in industrial environments that require high accuracy and stability.
How Does a PT100 Work?
A PT100 works by measuring the resistance changes in platinum wire that is heated or cooled by temperature. As the temperature of a platinum wire changes, so does its electrical resistance. An RTD, such as a PT100, is calibrated to produce a predictable change in resistance with respect to temperature. This predictable relationship is used to acquire temperature measurements.
PT100 sensors are measured in Ohms (Ω) and typically have a resistance of 100Ω at 0°C. The resistance of a PT100 sensor changes by approximately 0.385 Ω/°C for every degree Celsius of temperature change. Therefore, a PT100 sensor with a resistance of 138.5 Ω indicates that the temperature is 100°C (138.5-100=38.5 Ω, which means 38.5/0.385=100°C).
Duplex RTD PT100 Wiring Diagram
A duplex RTD PT100 consists of two PT100s that are wired in series. The wiring diagram for a duplex RTD PT100 is shown below:
| Color Code | Wire Name | Terminal Block (TB) |
|---|---|---|
| White | PT100W1 | 1 |
| Blue | PT100B1 | 1 |
| Red | PT100W2 | 2 |
| Yellow | PT100B2 | 2 |
To wire a duplex RTD PT100, follow these steps:
- Insert the PT100W1 wire into terminal block 1.
- Insert the PT100B1 wire into terminal block 1.
- Insert the PT100W2 wire into terminal block 2.
- Insert the PT100B2 wire into terminal block 2.
Note that the colors of the wires may vary depending on the manufacturer, so it is essential to consult the wiring diagram provided by the manufacturer.
FAQ
1. How do I know if my PT100 is working?
You can test your PT100 by connecting it to a multimeter and measuring its resistance. At room temperature, the resistance of a PT100 should be approximately 100Ω. If your PT100 is working correctly, you should get a predictable change in resistance as the temperature changes.
2. Can I use my PT100 in a hazardous environment?
Yes, you can use your PT100 in a hazardous environment as long as it is properly installed and protected. PT100 sensors are available in various enclosures, such as explosion-proof, flame-proof, and intrinsically safe, depending on the environment in which they will be used.
3. How can I improve the accuracy of my PT100?
You can improve the accuracy of your PT100 by calibrating it regularly, using high-quality wires and connectors, and ensuring that it is properly installed and protected. You can also use a compensating cable to eliminate any thermal gradients between the PT100 and the measuring instrument.
4. Can I use a PT100 for high-temperature applications?
Yes, you can use a PT100 for high-temperature applications as long as you select the appropriate sensor and wiring materials. For high-temperature applications, you may need to use a ceramic insulated or metal sheathed PT100 to withstand the high temperatures.
5. How do I connect my PT100 to a PLC?
To connect your PT100 to a PLC, you will need to use a temperature transmitter that converts the resistance of the PT100 into a voltage or current signal that can be read by the PLC. Typically, the temperature transmitter will have a standard 4-20mA output that can be connected to the PLC’s analog input.
Conclusion
Wiring a duplex RTD PT100 can be challenging, but it is essential to ensure accurate temperature measurements. By following the steps outlined in this article, you can easily wire your PT100 and enjoy its accuracy, stability, and repeatability. Remember to consult the wiring diagram provided by the manufacturer and take the necessary precautions when working with electrical components.
