HMD-1000 Internal

Humidity Sensor

The sensor used is 7Semi - SHT20 Humidity and Temperature Sensor Probe MRS Type I2C

It is an assembly using the SHT20 sensor from Sensirion:

3: Time for achieving 63% of a step function, valid at 25°C and 1 m/s airflow.

Without any airflow, the response time would increase. In the current chamber, the sensor is placed away from the airflow which is not satisfactory.

Prolonged exposure to extreme conditions may accelerate ageing:

Important points of the HM humidifier:

Very high to very low humidity range. Current sensor may not be best suited for this application

Vapor coming out at high temperature (water ebullition), the tubes are 1.5m (and there is combination with cold dry air) but the temperature at the end may still be high so the dew point at the sample is very high, it may be higher than the sample temperature. This may create a dew on the sample and we would actually be analyzing another type of tribology than dry/dry contact with humidity as we have a thin water film on the lower sample. From my understanding this is not told to customers and may not be fully understood by them.

Condensation on the tubes splashed onto the sample and modifying the testing conditions when going to high %RH (small diameter tube, temperature lower than the dew point, condensation must happen, higher diameter would reduce that splattering effect).

Property	Existing humidifier	Possible modifications
Humidity Sensor position	On the side + low air contact area	Full contact area + on the air path
Humidity Sensor range	5-95%	1. Tell the customer that use outside normal range (10-88%) diminishes expected lifetime. 2. SHT45 may be better suited (better resolution, lifetime, range…)
Chamber sealing	Side entrance, top exit	Sealed ball holder hole, side entrance and opposite side air exit. Can it be adapted to pressure test chamber (rod seal ⇒ usable in MTM liquid chamber)?
Humid/Dry junction	Close to the exit	Before the tube, right after the exit to reduce the turbulences when entering the chamber
Tubes length	Long	As short as possible without low/top points
Tubes diameter	6mm	Larger to reduce flow speed for similar flow rate
Airflow	No recommendation	Analysis to recommend input pressure range for airflow without water perturbation
Condensation on the sample, no dew point control	Probably high temperature air coming out of the tubes ⇒ High dew point ⇒ dew on the sample	Water layer presence notified to customer or full humidifier technology modification (ex: membrane humidifier)