RTD Installation and Maintenance 101: A Beginner's Guide

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⌚Timestamps:
00:00 - Intro
00:21 - How does an RTD work?
01:08 - How RTDs are Used?
04:13 - 2, 3, and 4-wire RTD
05:11 - RTD Protection
06:14 - RTD maintenance and troubleshooting
07:28 - Summary

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In this video, we're going to introduce you to the Resistance Temperature Detector commonly referred to as RTD.

We’ll talk about how the RTD works and how it’s used in industry to measure temperature. We’re also going to discuss regular maintenance, calibration, and troubleshooting of RTD circuits.

An RTD is a passive resistive device made from a metal that changes resistance with a temperature change. If the temperature increases, the RTD resistance increases.

In most applications, a current is passed through an RTD to determine temperature. Using the resulting voltage across it, the RTD resistance can be determined using Ohm’s Law.

The resistance changes almost linearly with a temperature change. A very good linear range for the Pt100 RTD is 0 ℃ to 400 ℃.

The relationship between temperature and resistance of an RTD is referred to as the temperature coefficient (Alpha). The Alpha of a Pt100 RTD is 0.00385 ohms/ohm/℃.

The Wheatstone Bridge was probably the most commonly used method originally. But, it's not so common anymore. The distance between the RTD and the bridge becomes an issue because of the introduction of lead wire resistance.

The Constant Current Source method is very popular. The voltage is a direct result of the resistance of the Pt100 and the constant current flowing through it.

An increase in lead wire resistance does not affect the Voltage V because the current through the RTD is not affected.

You will rarely see a 2-wire RTD used in an industrial application because of its inherent problems with resistance detection.

3-wire and 4-wire RTDs are the industry standards as issues with lead wire resistance are eliminated.

Probably the best and most accurate temperature measurement is made using a 4-wire RTD connected to a Constant Current Source transmitter.

The transmitter current is unaffected by the lead wire length. The voltage resulting from the constant current and the RTD temperature is detected by the transmitter.

The transmitter converts this detected voltage and sends a corresponding signal to a receiving instrument such as a PLC.

An RTD needs protection. A connection head is used to connect the RTD leads to the transmitter. The connection head also protects from nasty ambient conditions.

Further protection is provided by inserting the RTD sheath into a thermowell that is permanently housed in a pipe or a vessel. The thermowell protects from potentially damaging process fluids.

The RTD can be easily removed from the thermowell without interrupting the process.

Thermowells create issues such as a delay in detecting process temperature changes. Thermowell placement is also an important consideration.

A defective RTD will cause issues as well. You can perform a very quick and simple test by isolating the RTD and connecting an ohmmeter across it. The RTD will read a finite resistance value of approximately 110 ohms to 115 ohms depending on the ambient temperature.

The best way to isolate the problem is by using a process calibrator to replace the RTD in the measurement circuit.

The process calibrator can simulate the RTD by producing resistance and applying that resistance to the transmitter.

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What is an Instrument Calibrator?: https://realpars.com/instrument-calibrator

If you want to become an RTD expert, then our free course is perfect for you. Get all the tips and tricks on how to install & troubleshoot these devices like a pro.
Complete Introduction to RTDs: https://learn.realpars.com/courses/introduction-to-rtd

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Видео RTD Installation and Maintenance 101: A Beginner's Guide канала RealPars