How Does a Thermocouple Work?

This is a follow up on the previous post. 

A thermocouple consisting of two rods made of different metals joined to form one rod, registers a voltage proportional to the temperature difference between its two ends as a result of the Seebeck effect creating an electric potential difference from temperature gradient. Putting one end as sensor (or measurement junction) in optical contact through a camera lens with a distant object, will make it attain the same temperature as the object as an expression of thermal equilibrium just like an ordinary thermometer in contact with an object. Keeping the other end as reference junction at a known temperature makes it possible, after calibration, to read the temperature of the object.  

The thermocouple can also be used without calibration by varying the temperature of the reference junction until the voltage is zero. 

The essence is that a thermocouple reacts to temperature as prime sensor input. 

In climate science the following different narrative is presented: The input to the sensor is not primarily temperature but radiation as number of absorbed photons emitted by the object at temperature $T$, incorrectly claimed to scale with $T^4$, see earlier post, and so to allow temperature to be determined from sensing radiation by counting incoming photons. This scheme is claimed to be realised in a pyrgeometer which when directed to the sky on its display reports Downwelling Longwave Radiation DLR emitted by the sky contributing to substantial global warming of the Earth surface. The sensor of a pyrgeometer is a thermocouple, which thus is claimed to measure primarily radiation and not temperature.

But above we made clear that a thermocouple does not measure radiation, since it has no mechanism for counting photons as carriers of radiation. What a pyrgeometer does is to measure the temperature of the sky visible by infrared light which can be 255 K at 5 km altitude. This does not feed any climate alarmism. 

Unfortunately, the view that a pyrgeometer measures radiation propagated to sell climate alarmism, seems to be shared by climate skeptics like Happer and Spencer counteracting their criticism. A typical honest instrument, like a thermometer, reports what it primarily measures, but a pyrgeometer reports something else which is used to mislead into climate alarmism.