Flame proof (Ex d) Humidity transmitter

[spbdasan]

Hi,
We could not find any flame proof (Ex d) type humidity transmitter for hazards area in the market, while some manufacture for ?EX- d ?temperature transmitters and also for ?EX i? humidity transmitters.
If someone knows the ex d humidity transmitter brand please let me know.
Or share your knowledge why there is no ex d humidity transmitter in the market?

Thanks,

 

[GoldDigger]

Hi,
We could not find any flame proof (Ex d) type humidity transmitter for hazards area in the market, while some manufacture for ?EX- d ?temperature transmitters and also for ?EX i? humidity transmitters.
If someone knows the ex d humidity transmitter brand please let me know.
Or share your knowledge why there is no ex d humidity transmitter in the market?

Thanks,

I would guess that the explanation is in the nature of the measurement being made.
A temperature sensing element (thermocouple, resistor, bimetal, semiconductor,...) can be isolated from direct contact with the air or other medium by a protective sheath and still be at a temperature equilibrium with it.
But the active surface of a humidity sensor must be in direct contact with the gas (typically air and water vapor) that it is measuring. That would mean that it would be directly exposed to combustion products, including highly reactive molecules and ions , in addition to the high temperatures.