2-color Pyrometers

2-color pyrometers (also called ratio pyrometers or two-channel pyrometers) measure as opposed to radiation pyrometers (also called 1-channel pyrometers) in two spectral ranges simultaneously and determine the temperature by calculating the radiation ratio (quotient). In this method it is not necessary to know the emissivity of the material. It is reduced out because the radiation ratio remains constant at a neutral attenuation of infrared radiation (by dust, smoke …). Ratio pyrometers are available in series Metis M3 and H3 in various versions:

Metis M3 / Metis H3

Metis M3 / H3 Heavy Duty

Short-wave measurements of metals, ceramics, composites, semiconductor, wafers, molten glass…

The material to be measured largely determines which spectral range of the pyrometer should be or has to be selected. For metal measurements, the shortest possible spectral range for a precise measurement is advantageous. As the short-wave spectral range begins at somewhat higher temperature, potentially a model with the slightly longer wave spectral range has to be selected.

Temperature ranges from 600°C
from 300°C

Spectral range 0.75 - 1.1 µm

Model	Spectral range λ	Temperature ranges	Response time	Distance ratio/ Smallest spot size Ø	Optics	Sightings
Metis M311	0.75 – 1.1 µm	600–1400°C 650–1500°C 750–1800°C 900–2500°C 1000–3000°C 1100–3300°C	< 1 ms	377:1 / 0.8 mm	Foc, MFoc, FFoc	LA, VF, C
Metis H311	0.75 – 1.1 µm	600–1100°C 650–1300°C 750–1400°C 900–1800°C 1000–2000°C 1100–2200°C 1300–2500°C	< 80 µs	280:1 / 0.5 mm	Foc, FFoc	LA, VF, C

F: Fixed optics, Foc: Integrated focusable optics, FFoc: Focusable fiber optics,
MFoc: Motorized focus optics, LA: Laser aiming, VF: View finder C: Camera

Spectral range 1.45 - 1.8 µm

Model	Spectral range λ	Temperature ranges	Response time	Distance ratio/ Smallest spot size Ø	Optics	Sightings
Metis M322	1.45 - 1.8 µm	300–1000°C 350–1300°C 500–1800°C 800–3000°C 1000–3300°C	< 1 ms	377:1 / 0.8 mm	Foc, MFoc, FFoc	LA, VF, C
Metis H322	1.45 – 1.8 µm	350–800°C 550–1400°C 700–2300°C 1000–2500°C	< 80 µs	280:1 / 0.5 mm	Foc, FFoc	LA, VF, C

F: Fixed optics, Foc: Integrated focusable optics, FFoc: Focusable fiber optics,
MFoc: Motorized focus optics, LA: Laser aiming, VF: View finder C: Camera

Area of Application / Benefits

Polluted viewing glasses or dust and smoke keeps the measurement largely unaffected.
Measuring objects smaller than the pyrometer’s spot size can be measured
The short pyrometer wavelength ranges are ideal for metal measurement
Fiber optic models can be used in ambient temperatures up to 250°C (on the optical head) without additional cooling.

Special Features

Very fast data acquisition: Standard version with < 1 ms response time, High-speed design provides the measurement result (the response time) depending on the model with 40 or 80 µs to the outputs.
Switchable to 1-channel mode for use as a normal radiation pyrometer.
Software representation of the measured temperatures of both channels allow to detect whether the measurement is wavelength dependent and can be carried out or the setting of the emissivity slope is required or the measurement is not possible.
A monitoring function enables to detect the degree of contamination of the optics or a viewing window and identifies interferences (dust…) in the beam path and gives an alarm if required.
The switch-off level defines a signal level at which the temperature measurement is switched off, because no reasonable formation of quotients is longer possible (eg, if pollution in the pyrometer’s field of view is too strong). Practical Tip: The switch-off level should be set to 10%

Please Notice when Using a Ratio Pyrometer

Targets with the same emissivity on the two wavelengths can be measured without emissivity slope setting.
Emissivity changes must affect the same on both channels (wavelengths).
When measuring objects with different emissivities on the two wavelengths (e.g. bare unoxidized metal surfaces) the emissivity ratio must be set for accurate temperature measurement.

pdf-Download Pyrometer Product Overview: Device designs, pyrometer technique, criteria for selecting a Sensortherm pyrometer, model overview, overview of available spectral ranges, features, accessories, software support, quality control and services.