IR Temperature Sensing - Pyrometry
Non-contact temperature measurement is an optical measurement based on the property of all materials to send out electromagnetic radiation (infrared radiation). The infrared measuring instrument (pyrometer or thermal imager) uses this radiation to determine the temperature.
Today typically spectral responses of infrared thermometers are in the near, middle and distant infrared. To choose the correct measuring instrument for a certain application different properties of the measuring object have to be taken into consideration, such as temperature, material, and size.
The Temperature Range:
Our pyrometers measure temperatures from -40 to 3500 °C. The instruments are available in different temperature ranges. The selection of the temperature range depends on the application.
The Spectral Range
The material of the measured object demands the correct selection of the optimum spectral range of the pyrometer for a certain application. Therefore the correct spectral range is one of the most important features.
Typical spectral ranges are:
|0.676 µm:||Measurement of molten metals (min. 1100 °C)|
|0.8 ... 1.1 µm:||Measurement of molten glass, metals, ceramics (min. 600 °C)|
|1.45 ... 1.8 µm:||Measurement of metals, ceramics (min. 250 °C)|
|2.0 ... 2.8 µm:||Measurement of metals (min. 75 °C)|
|3 ... 5 µm||Measurement of metals, ceramics (min. 5 °C)|
|3.43 µm||Measurement of PE and PP foils (min 50 °C)|
|3.9 µm||Measurement in flame heated furnaces (min. 75 °C)|
|5.14 µm:||Measurement of glass surfaces (min. 100 °C)|
|8 ... 14 µm:||Measurement of non-metal surfaces and coated metals (min. -40 °C)|
The emission coefficient is the relationship of the emission output of an object to the emission output of a black body radiation source at the same temperature. It is influenced by the object's material and changes with the wavelength, the temperature or other physical values.
The emission coefficient of an object is the most important value when determining its temperature with a pyrometer. If one wants to measure the true surface temperature of an object with a pyrometer one must know the emission coefficient, or emissivity, of the object and enter its value in the pyrometric measuring system.
In principle the emissivity of a material is influenced by wavelength, temperature, etc.. Therefore emissivity tables can only give an indication of the exact emissivity for different applications.
A table with emissivities of various materials can be downloaded. (314 KB)
The Field of View
The dimensions of the measured object determine the required spot size of the pyrometer. At least the spot size has to as big as the measured object to achieve a correct temperature measurement. The spot sizes are dependent on the type of pyrometer and measuring distance, they can be calculated using the distance ratio or field of view (FOV).
FOV = measuring distance / spot size
(e.g. 240 : 1 means: in a distance of 1200 mm the spot size is 5 mm).
The response time is the time interval between the instant of an abrupt change in the value of the measuring temperature and the instant from which the measured value of the pyrometer remains within specified limits.
For easy alignment of the pyrometers to the measuring object, different sighting systems are available:
- LED aiming
- Laser aiming
- View finder
- TV camera
Laser targeting light
For easy alignment to the measuring object the pyrometers can be equipped with a laser targeting light. This is a visible red light with a wavelength between 630 and 680 nm and a maximum power of 1 mW. The laser is classified as product of laser class 2.
IMPAC pyrometers are designed for the use in industry under rough conditions. The housings of the fixed pyrometers are made of stainless steel or die cast aluminum with the protection class of IP65. The housings of the portables are made of robust plastics. Available are:
- Compact pyrometers with integrated lens
- Fiber optic pyrometers (LO)
Different pyrometers provide different outputs. Analog outputs and digital interfaces are available. Some pyrometers have various switchable outputs, the output at the IN 3000 has to be selected when ordering.
- Analog output 0 ... 20 mA or 4 ... 20 mA
- Analog output 10 mV/°C
- Analog output 0 ... 5 V
- Analog output thermo couple type J or K
- Digital interface RS232 or RS485