How To Select A Temperature Measurement Device For Your Process //
The challenge is choosing the right device for the application. There are many types available. Some will be more suitable than others based on their level of accuracy, tolerances and how they work.
Below, we'll cover the various options. We'll also talk about accuracy and precision, and how it's possible to place too much emphasis on both. You'll also learn how to select a thermocouple, one of the most commonly-used measuring devices.
Types Of Temperature Measurement Devices
The most popular options include thermocouples, resistance temperature detectors (RTDs) and thermistors. Lesser-used devices - at least, with respect to industrial applications - include bimetal thermometers, glass-liquid thermometers and infrared radiation thermometers.
Thermocouples are relatively inexpensive. They can measure over a wide temperature range. Those two features make them a popular choice. The downside is their lower degree of accuracy compared to other types of sensors.
RTDs can deliver more accurate readings than thermocouples, making them a good option for environments that require a high degree of measuring accuracy. But they do so over a narrower temperature range. They also deliver readings more slowly.
Thermistors are highly-sensitive to temperature changes. Thus, they're capable of delivering highly-accurate readings. However, they can only operate in a limited temperature range. That makes them useful in specialty applications, but a poor choice in most others.
Accuracy And Precision In Temperature Sensors
Accuracy in temperature measurement is, of course, important. But it's also important to understand how it can sometimes be overemphasized. Moreover, it's worth noting how accuracy differs from precision as the two terms are often mistakenly used interchangeably.
Accuracy refers to how close a measurement is to its true value. For example, if one were shooting at a target, accuracy would reflect a shot's nearness to the target's center. The nearer it is, the more accurate the shot.
Precision refers to consistency. Continuing with our target-shooting example, precision would reflect how closely together multiple shots land on the target. The smaller the area over which the shots are distributed, the greater the precision.
Accuracy and precision are key elements to consider when it comes to selecting a temperature sensor. It's important, of course, for the device's measurements to accurately reflect the amount of kinetic energy (in degrees) in an application. At the same time, it's important that there's an acceptably-low degree of variance in the measurements.
Having said that, some applications require a high level of accuracy and precision in temperature measurements. Others don't. Process managers often overemphasize the importance of such requirements for their environments. They choose sensors that are highly accurate and precise, but consequently pose a higher cost than necessary.
Factors To Consider When Selecting A Thermocouple
Thermocouples are commonly used in industrial applications because they're inexpensive, versatile and capable of delivering fast results. It's worth highlighting the most important factors to consider when choosing one.
Thermocouples are available in many different designs, some of which are specifically suited to certain types of applications. The design is reflected by a letter, such as B, E, J and K. The letter indicates the type of material used for the device's positive and negative conductors. Those materials, in turn, imply the temperature range over which the thermocouple can be used to take measurements.
Because thermocouples lack the high degree of sensitivity to temperature changes seen with RTDs and thermistors, it's important to be familiar with their potential for error. They come in different forms, including noise errors, offset errors and cold-junction compensation errors.
Junction style is another important factor to take into account. Thermocouples come in 3 different designs: grounded, ungrounded and exposed. Each design comes with its own set of pros and cons. For example, a grounded design delivers fast responses to temperature changes, but operates with a higher likelihood of error. An exposed thermocouple is even faster, but is unsuitable for many environments, particularly those that involve corrosive fluids.
Choosing the right temperature measurement device for your application can be a challenge. However, that challenge is made simple when you rely on the trained support staff and service engineers at AEI Applied Engineering. Contact us for help on selecting the perfect solution for your process.