Temperature Measurement

Temperature measurement is the process of quantitatively determining the temperature of an object or environment by means of an instrument or device. Temperature is a physical quantity that describes how hot or cold an object is, usually expressed in degrees Celsius (°C), Fahrenheit (°F), or Kelvin (K).

Thermometers, controllers and transmitters for the process industry. Apure offers a complete assortment of compact thermometers, modular thermometers, thermowells, measurement inserts, transmitters and accessories for all types of process industries such as Oil & Gas, Chemicals, Food & Beverage, Life Sciences, Primaries & Metal, Power & Energy.

Bimetal thermometer is a kind of field instrument for measuring medium and low temperature. It can directly measure the temperature of liquid, steam and gas medium in the range of -80℃ ~ +500℃ in various production processes.

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Temperature controller is regulating the integration of intelligent temperature control instrument, it adopted the full digital integration design, programmable temperature curve or point temperature control, multiple PID adjustment.

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Temperature transmitter using thermocouple, thermal resistance as a temperature measuring element, from the temperature measuring element output signal to the transmitter module, after stabilizing filter, operation amplification.

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Common Temperature Measurement Methods

Contact measurement

  • Liquid thermometers: Use the thermal expansion properties of liquids to measure temperature.
  • Thermocouple: A joint of two different metals is placed at a measurement point and generates a thermal potential proportional to the temperature.
  • Thermistor: Measures temperature by utilizing the property of a material’s resistance to change with temperature.

Non-Contact Measurement

  • Infrared thermometer: Measures temperature by detecting infrared radiation from an object.
  • Fiber optic temperature sensor: Measures temperature by using the temperature dependence of light propagation in an optical fiber.

What are the units of temperature measurement?

  • Degrees Celsius (℃): the current international unit of temperature, the freezing point of water is 0 ℃, boiling point of 100 ℃.
  • Fahrenheit (℉): mainly used in a few countries such as the United States, the freezing point of water is 32℉, the boiling point is 212℉.
  • Kelvin (K): The unit of thermodynamic temperature, 0K is absolute zero, equivalent to -273.15℃.

What are the considerations for temperature measurement?

  • Sensor selection: Select the appropriate sensor according to the temperature range, response speed, accuracy and other requirements of the measurement object.
  • Calibration: Regularly calibrate the temperature measurement instrument to ensure the accuracy of the measurement results.
  • Environmental influences: Temperature measurement will be affected by ambient temperature, humidity, air pressure and other factors, need to consider environmental compensation.
  • Heat conduction: Measurement should avoid the measurement error caused by heat conduction.

FAQ

Thermometers are usually corrected by comparison with standard thermometers or at fixed points. According to the fixed point correction, the freezing point (0℃) and boiling point (100℃) of water can be conveniently used as the fixed point. Here’s an easy way to correct for the freezing point of water: put clean crushed ice in a thermos cup and fill it with pre-cooled distilled water just enough to submerge the ice. Gently tamp the ice with a glass stick to remove air bubbles from the ice water mixture. The pre-cooled thermometer is then inserted vertically into the ice so that its zero scale line is exposed about 5 mm above the ice surface. After about 15 minutes, record the thermometer readings at 1-minute intervals. The actual position of the zero scale line of the thermometer is the same data obtained several times in a row as the reading stabilizes. The “zero error” value can be corrected in the future temperature measurement.

Thermometer is a tool that can accurately judge and measure temperature. It is divided into pointer thermometer and digital thermometer. A variety of thermometers have been designed and manufactured for different purposes.

Called the thermostat, temperature controller, also called temperature control switch, temperature protector, divided into two categories, mechanical and electronic, it is mainly according to the working environment temperature changes, physical deformation inside the switch occurs, resulting in a certain special effect, produce the conduction or disconnect action – series of automatic control components, or electronic parts at different temperatures, Working state of different principles to provide temperature data to the circuit, to collect temperature data power supply. Temperature controller is a kind of automatic adjustment device which can make the temperature in the box change within the specified range by using the principle of thermal expansion and contraction of the sensitive liquid and incompressible liquid.

There are mechanical and electronic ones.

Mechanical use of two layers of metal with different thermal expansion coefficient pressed together, temperature change, his bending will change, when bending to a certain degree, connected (or disconnected) loop, make refrigeration (or heating) equipment work.

Electronic through thermocouple, platinum resistance and other temperature sensing devices, the temperature signal is converted into electrical signals, through MCU, PLC and other circuit control relay to make heating (or refrigeration) equipment work (or stop). There are mercury thermometers, which have contacts that connect to the mercury when the temperature is up.

Bimetal thermometer is a kind of measuring instrument to measure medium and low temperature. It can measure the temperature of liquid vapor and gas medium from -80℃ to 500℃ in various production processes. The main component of the bimetal thermometer used in general industrial production is a multi-layer metal sheet composed of two or more kinds of metal sheets stacked together, using two different metals in the temperature change when the expansion of the different degree of principle. It is based on a bimetal sheet wound into a circular bending. When one end is heated and expands, it drives the pointer to rotate, and the working instrument shows the temperature value of the thermoelectric potential.

Temperature transmitter using thermocouple, thermal resistance as a temperature measuring element, from the temperature measuring element output signal to the transmitter module, after stabilizing filter, operation amplification, nonlinear correction, V/I conversion, constant current and reverse protection circuit processing, converted into a linear relationship with the temperature of 4 ~ 20mA current signal 0-5V/0-10V voltage signal, RS485 digital signal output.

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