FAQ – Humidity Measurement

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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
 filter-1
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
 filter-2
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
 filter-3
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
 filter-4
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
 filter-5

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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

chart-1

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.

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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)

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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

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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.

Long term test OUTSIDE CLIMATE

Long term test INDOOR CLIMATE

Long term test SWIMMING HALL

Long term test COW STABLE

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