Digital Pyrometer Technology

What are the advantages of digital pyrometers? All Sensortherm pyrometers work with the self-developed direct detector signal digitization. Here, the analog infrared detector signal is digitized via a fast and high-resolution A/D converter right at the beginning of the signal chain, in order to be able to carry out all further signal processing operations in a microcontroller, instead of controlling them via analog adjustments of the detector current.

Pyrometer Construction Digital Technology

From the detector signal to the output signal, a variety of signal adjustments must be made.

Advantages of Digital Technology Compared to Analog Based Devices

  • Emissivity adjustment: The adjustment of the emissivity at the pyrometer is calculated by multiplication in the microcontroller.
    • Advantages of digital technology: With Sensortherm pyrometers, it does not matter if they are operated at 10% or 100% emissivity, it is always calculated the physically exact value.
    • Disadvantages with analog technology: This is not the case with devices with analog correction. Simply adjusting the emissivity from 1 to 0.5 can lead to additional measurement errors in the range of one percent. These can increase to several percent if the ambient temperature of the pyrometer is increased to above 50°C. These errors are usually not noticed by the user because the emissivity is not known anyway. However, if the pyrometer is replaced, the reading changes.
  • Quotient formation: 2-color pyrometers precisely and digitally divide the signals of the two detectors in the microcontroller in order to determine the measurement temperature.
    • Advantages of digital technology: Even at the beginning of the temperature range, accurate measurement results are still obtained where only low signal levels are present.
    • Disadvantages with analog technology: With analog devices, the previously logarithmized signals of both channels are simply subtracted, whereby the quotient formation takes place analog with the same errors as with the analog emissivity adaptation.
  • Ambient temperature compensation: All pyrometers are adjusted and compared on calibration sources at standard laboratory temperatures of 23°C and with an emissivity of 100%. In practice, however, neither the 23°C ambient temperature nor the 100% emissivity can be found.
    • Advantages of digital technology: Sensortherm pyrometers not only have the advantages of mathematical emissivity adjustment, the devices are also continuously adjusted to changing temperature conditions with several digitally stored compensation curves to ensure always accurate and reproducible measurement results, quasi a 3D adjustment.
    • Disadvantages with analog technology: For devices with analog ambient temperature compensation, due to the analog processing the error can be greater than 20°C with a set emissivity of 50% and a measurement temperature of 1000°C. If the ambient temperature is much higher than the standard 23°C used in the calibration laboratory, the error can easily double. This error is not specified in any pyrometer data sheet and is not determined in any calibration laboratory.
  • Linearization: The infrared detector signal is not linear.
    • Advantages of digital technology: The detector signal is digitally linearized at several interpolation points for different ambient temperatures in order to comply with the company’s own narrow accuracy specifications over the entire temperature range.