How to Keep the Lens of a Pyrometer Clean

The lens of every infrared temperature sensor must be kept clean and dry to ensure the pyrometer has a clear view of the target. The simplest way to do this is to purge the lens continuously with clean air, preventing dust and moisture from reaching it. Here is how to use the air purge collar. 

1. Order a compatible air purge collar

It’s OK if you already have the sensor, but not the air purge collar. You can add the air purge collar at any time. A choice of air purge collar accessories is available to fit every Calex sensor:

Air Purge Collar Model Compatible With
APSW Sensors from the following ranges, with 2:1 optics: PyroCouple, PyroEpsilon, PyroBus, PyroCAN, PyroMini, PyroMiniUSB, PyroMiniBus
APSN All the above sensors, with all optics except 2:1
APL PyroUSB (all models)
APM ExTemp (all models)
APF FibreMini (all models)
APN PyroNFC (all models)
APC PyroCube S, G, P, MB
APCF PyroCube F, XSB

2. Fit the air purge collar to the sensor


The air purge collar is screwed onto the threaded part of the sensor, after the mounting nut. This diagram shows how: 


If you are mounting the sensor through your own metalwork instead of the Calex mounting bracket, we recommend the thickness is 2 mm or less for use with the air purge.

The air fitting has 1/8″ BSPT thread at both ends. You can unscrew it and replace it with an alternative air fitting if you prefer.


The air purge is screwed into a dedicated mounting thread over the lens of the PyroCube sensor. There is a female push-fit connection for a 4 mm air line.


The air purge screws onto the sensing head mounting thread after the FibreMini or ExTemp sensor has been fixed into position using the mounting nuts.

There is a barb-type fitting with diameter 5 mm. If you prefer to use your own air fitting, the thread is M5.


The air purge is attached to the face of the PyroNFC sensor using two longer mounting screws, which are supplied.

This air purge collar has the same barb-type air fitting as above, with a diameter of 5 mm and an M5 thread.

3. Supply some air

The air should be clean and dry (“instrument” air is recommended). Only a small amount of air is necessary – just enough to provide some positive pressure in front of the lens, keep it dry and prevent dust getting in. Less air is better than more. We suggest a flow rate of 5 to 15 litres per minute for most sensors (5 l/min max for PyroCube).

4. Happy measuring

After you start using the air purge collar, check the lens now and again to make sure it is working effectively. The lens may still need cleaning occasionally – if you find this is necessary, clean it with a soft lens cloth and water or isopropyl alcohol.

Don’t hesitate to get in touch with us if you have any questions.


By Anthony Smith