3 Wire RTD Wiring Diagram

A 3 wire RTD or resistance temperature detector is a sensor used to measure temperature. They are widely used in industrial and scientific applications where high accuracy is required. RTDs are preferred over other temperature sensing devices because they are stable, repeatable, and accurate. In this article, we will discuss the wiring diagram for a 3 wire RTD, its working principle, types, and applications.

Working Principle of 3 Wire RTD

A RTD works on the principle of changing resistance with temperature. It consists of a sensing element made up of metals whose resistance varies with temperature. These metals are usually platinum, nickel, or copper. When the temperature changes, the resistance of the sensing element also changes. Thus, by measuring the resistance of the sensing element, we can measure the temperature.

In a 3 wire RTD, two wires are connected to the sensing element, and the third wire is used to compensate for the effect of lead resistance on the measurement. The resistance of the two wires connected to the sensing element is measured, and the third wire is used to measure the resistance of the connecting wires. This helps to eliminate the effect of lead resistance on the measurement.

Wiring Diagram of 3 Wire RTD

The wiring diagram of a 3 wire RTD is shown in the table below:

Wire Color Connection
Red Positive Lead
Blue Negative Lead
Green Compensation Lead

The red and blue wires are connected to the sensing element, and the green wire is connected to the terminal block of the RTD transmitter. The transmitter is connected to the control system that processes the temperature readings.

FAQ

What is the difference between a 2 wire and 3 wire RTD?

A 2 wire RTD has two wires connected to the sensing element, and the resistance of these wires is measured along with the resistance of the sensing element. This can introduce errors because the resistance of the connecting wires can change with temperature. In a 3 wire RTD, the compensation wire is used to cancel out the effect of lead resistance on the measurement. This results in more accurate temperature measurements.

What are the types of RTDs?

The most commonly used types of RTDs are:

  • Platinum RTD (PT100)
  • Nickel RTD (Ni100)
  • Copper RTD (Cu100)

What are the applications of RTDs?

Some of the common applications of RTDs are:

  • Temperature measurement in chemical processes
  • Temperature measurement in power plants
  • Temperature measurement in food and beverage industry
  • Temperature measurement in pharmaceutical industry

What is the accuracy of RTDs?

The accuracy of RTDs can vary depending on the type of RTD and the measurement system used. Typically, the accuracy ranges from ±0.1°C to ±0.5°C.

How can I calibrate an RTD?

To calibrate an RTD, you will need a calibration bath, a reference thermometer, and a temperature controller. First, immerse the RTD in the calibration bath and measure its resistance at different temperatures. Compare the readings with the readings of the reference thermometer. Adjust the temperature controller to match the reference thermometer. Repeat the process until the RTD readings match the reference thermometer readings.

In conclusion, a 3 wire RTD is a highly accurate temperature sensing device that is widely used in industrial and scientific applications. Its wiring diagram is straightforward, and it is easy to use in most temperature measurement systems. By understanding its working principle, types, and applications, you can choose the right RTD for your temperature measurement needs.