What´s the secret to a perfect cup of coffee? Temperature. And how does a coffee maker brew at the right temperature? With a temperature sensor. Accurate measurement and control equal a great sip of java – or other product that requires a certain temperature.
While most folks know at least one or two sensors, the market holds so much more, a device for nearly every need. So today, we’ll review the types of temperature sensors used across the industry.
Resistance temperature detector (RTD)
This device also measures by resistance. Most RTDs use platinum as a measuring element. When we say PT100, we mean at zero degrees Celsius, the RTD should measure a resistance of 100. The range for an RTD varies from -240 to 649 ˚C.
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- Good linearity
- Great accuracy
- Stable response (typically 0.05 percent per year with respect to span).
- Low output resistance
This type measures the force created between two dissimilar metals joined at a junction. Depending on the materials, thermocouples fall into several classes – J, K, N, R, and more.
You’ll find these in places like oil refineries, which need a high range of measurement.
- Wide temperature range (0 to 1800 °C)
- Less stable than RTDs
- Less accurate than RTDs
This non-contact type pops up in difficult process conditions like those with high heat or rotating equipment. An infrared (IR) sensor uses electromagnetic radiation to measure up to 1800 ˚C.
IR sensors work well to monitor engines and boilers as well as large areas and moving objects.
- Good accuracy
- No interference
- Easy and precise measurement
- Minimal cable
- Ineffective in fluids
- Fragile and easy to contaminate
A “thermally sensitive resistor,” also known as a semiconductor sensor, monitors heat by measuring changes in resistance. We classify them by negative or positive temperature coefficient (NTC or PTC), depending upon the resistance change.
Medical equipment, cars, toasters, and many more use thermistors.
- Fast output response
- Good sensitivity
- Minimal lead resistance error
- Limited range (-40 to 150 degrees Celsius)
- Non-linear measurement
As the name suggests, this device uses two joined metals with different expansion rates to measure temperature. And these sensors come in a handful of shapes like spiral, helical, flat, and cantilever.
- Limited range (-80 to 400 ˚C)
- Regular use can result in warping