Which filter for which application?
How often is it necessary to recalibrate E+E humidity transmitters?
Are the E+E sensors wettable and how do you clean them?
How fast is the response time of humidity probes?
How is the long term stability of the E+E sensors in normal environmental conditions?
Which filter for which application
DUST FILTER CAPS
To protect the active surface of the humidity sensor from unwanted pollution, the sensor probes can be fitted with various dust filter caps, depending on the application.
| membrane filter: for room applications, minor pollution in HVAC environment, order code: HA010101 |
response time: size of pores: suitable up to: |
20 s 1 µm 80degC |
 |
| plastic grid: mechanical protection in clean atmospheres, very short response times order code: HA010104 |
response time: size of pores: suitable up to: |
5,5 s — µm 120degC |
 |
| sintered stainless steel filter: for hostile industrial environment, food applications, mechanical and thermal stress order code: HA010103 |
response time: size of pores: suitable up to: |
30 s 10 µm 180degC |
 |
| PTFE filter: chemical aggressive environment at high temperatures order code: HA010105 |
response time: size of pores: suitable up to: |
13,5 s 50 µm 180degC |
 |
| metal grid filter: high humidity applications, if there is saturation or quick changing humidity cycles; order code: HA010106 |
response time: size of pores: suitable up to: |
7 s 100 µm 120degC |
 |
How often is it necessary to recalibrate E+E humidity transmitters?
It is necessary to check the performance of the instruments from time to time with reference measurements, which show the steady changes taking place during long periods of time.
According to work certificates confirming the calibration accuracy and measurement reliability.
The calibration interval depends on the
- working range of the humidity and temperature
- particular application
- pollution
Recommended recalibration intervals
first value for measurement accuracy in the range of ± 2% r.H.
second value for measurement accuracy in the range of ± 5 % r.H.
Are the E+E sensors wettable and how do you clean them?
E+E capacitive humidity sensor elements are fully wettable and cleaning is very easy. The construction of the elements is robust and mechanically stable.
Cleaning can be done using distilled water or pure Isopropyl alcohol, industrial grade. (for example in an ultrasonic cleaner)
How fast is the response time of humidity probes?
typical response time t50 for different sensor types:
| capacitive | resistive | LiCl | Dew point mirror |
electrolytic | fiber |
| < 15 s | < 60 s | < 5 min | < 60 s | < 30 min | < 10 min |
typical response time for E+E transmitters:
| FILTER TYPE | t10/90[s] | FILTER TYPE | t10/90[s] |
| wihtout filter | 5,5 | membrane filter cap | 20 |
| sintered stainless steel filter | 30 | sintered PTFE filter | 13.5 |
| metal grid | 7 |
How is the long term stability of the E+E sensors in normal environmental conditions?
LONG TERM TEST ‘OUTSIDE CLIMATE’
EXPERIMENT
10 humidity / temperature transmitters are tested since 1993 at a meteorological station near the city of Linz in Austria between two motorways. Extremely hazardous environmental conditions. (High air pollution, more than 70,000 cars a day)
RESULTS
The transmitters operate without any failure since 1993. There is no deviation between transmitters. The long term drift related to the reference humidity is approximately 4 % RH over a period of 4 years. Recalibration is not necessary The test will be continued.
LONG TERM TEST ‘EXTREME INDOOR CLIMATE’
EXPERIMENT
4 humidity / temperature transmitters were installed on the loft of a residential building. At this site there are very unstable climate conditions, fluctuating values in the range of -10 – +50 °C and between 20 and 90 % RH.
RESULTS
After 3 years there is a maximum humidity deviation of -3% RH. There is no need for recalibration. The test will be continued.
LONG TERM TEST ‘SWIMMING HALL’
EXPERIMENT
Operation of 10 humidity / temperature transmitters in the climate control system of a swimming hall with chlorine. The temperature ranges between 20-40 °C and the relative humidity between 30 and 50 % RH
RESULTS
All transmitters are staying at the same value. The humidity drift is less than 2%. (see standard deviation in the charts). There is no deviation in humidity or in temperature. The test will be continued
LONG TERM TEST ‘COW STABLE’
EXPERIMENT
After one year of operation in a cattle stable and henhouse with a very high ammoniac concentration the transmitter was checked and compared with the initial characteristics.
RESULTS
Looking at the characteristics curve in the humidity range between 40 and 80 %rH, there is hardly no deviation noticeable. In the high and low humidity range the deviation is a little higher, but can be compensated by special humidity calibration.