The emissivity of the target is important in IR temperature measurement. If this is not known or changes during the measurement, a measurement error is likely to occur. The emissivity of the target does not affect the measurement performance of the new thermoMETER CTratio. The sensor measures the temperature using two short wavelengths close to each other and obtains the quotient from this. The influence of the emissivity is therefore suppressed. Error-free measurement is also possible even when the IR radiation is weakened by 95% due to smoke or steam. The sensor provides a measuring range of 700°C to 1800°C at a maximum ambient temperature of 250°C without cooling. For small targets at a variable distance, the distance of the focal point can be modified by simply adjusting the lens. The completely passive sensor is connected to the electronics using an optical fibre. Therefore, electromagnetic fields have no influence on the sensor. If required, the thermoMETER CTratio can also measure using only one wavelength. The comprehensive interfaces (current, voltage output, optional: USB, RS232, RS 485, CAN, Profibus, Ethernet) enable fast integration in many different process environments.