ROTRONIC Hygromer CS 30 Humidity Sensor

Transcription

1 ROTRONIC Hygromer CS 30 Humidity Sensor Based on a unique technology, the CS 30 capacitive humidity sensor is designed specifically for high volume applications where high quality is as important as cost. Features: Wide range of operating temperatures Fast response time Durable and long term stable Chemically resistant Small dimensions Technical data: Humidity measuring range %RH Temperature operating range C Typical capacitance at 30 %RH and 23 C Typical sensitivity Linearity at 23 C when calibrated at 35 and 80 %RH Hysteresis Settling time t 90 Excitation Voltage 300 pf ± 40 pf 0.45 pf / %RH ( %RH) ± 2.0 %RH ( %RH) see linear deviation table < 2.0 %RH < 10 sec. (10! 80 %RH; V Air = 2m/sec.) alternating, must be free of DC component ± 12 V maximum, peak to peak khz (50 khz recommended) Dimensions: 3,8 mm 10 mm 10,8 mm 0,4 mm 2,54 mm Rotronic July 2001 Page 1/5

2 Sensor Characteristic at 23 C: Capacitance (pf) Relative Humidity (%RH) Linearity after calibration at 35 and 80%RH: The following table shows the deviation from a perfect linear response when the sensor is associated with a linear electronic circuit. The data is valid at 23 C, after adjusting the circuit by exposing the sensor to 35 %RH and 80 %RH (offset and gain adjustment). Rel. Humidity [%RH] LDR - deviation [%RH] Example: the humidity output reads 18.5%RH when the sensor is exposed to 20%RH. Linearity after calibration at two values other than 35 and 80%RH: The linearity of the humidity signal depends on the choice of the two nominal humidity adjustment points by the circuit designer. When the humidity adjustment points are two values other than 35 %RH and 80 %RH, the linearity of the humidity signal can be derived from the %RH table as follows: LD = (LDR LDR1) (LDR2 LDR1) x (RH RH1) / (RH2 RH1) with: LD: linear deviation at the humidity RH [ %RH], after adjustment at RH1 and RH2 RH: actual value of relative humidity [%RH] RH1: first calibration point [%RH] RH2: second calibration point [%RH] LDR: linear deviation at the humidity RH [ %RH], as per the above table LDR1: linear deviation at the humidity RH1 [ %RH], as per the above table LDR2: linear deviation at the humidity RH2 [ %RH], as per the above table Example: linear deviation at 50 %RH, after adjustment of the sensor and associated electronics at 11.3 %RH and 75.3%RH (values that are not in the table are interpolated) ( ) ( ) x ( ) / ( ) = 1.55 %RH When the sensor is exposed to 50%RH, the humidity signal reads %RH. Linearity and measurement accuracy - can be improved by correcting the output signal either digitally or with an analog circuit. Rotronic July 2001 Page 2/5

3 Humidity-Temperature Operating Limits: Humidity (%RH) Temperature ( C) Exceeding the above limits will affect the sensor characteristic response and may permanently damage the sensor. In some cases, the sensor can be regenerated by baking it at 120 to 140 C for a few hours. Temperature compensation of the humidity signal: As a general rule, the response of any humidity sensor is affected by temperature. Depending on the temperature range of the application, the electronic circuit associated with the CS 30 sensor should incorporate a temperature compensation so as to maintain measurement accuracy. The following table shows the compensation that should be added to the linearized sensor signal at different temperature and humidity conditions: Humidity! Temperature 0 %RH 10 %RH 35 %RH 50 %RH 80 %RH 95 %RH - 20 C C C C C C Notes: The above table assumes that humidity calibration was done at the temperature of 23 C Because relative humidity is normally calibrated at room temperature (here 23 C), the humidity sensor and associated electronics measure humidity in reference to liquid water even at temperatures below freezing. At a temperature of -20 C, this means that the maximum reading is about 82 %RH, which corresponds to 100 %RH (saturation) when humidity is referred to ice. Rotronic July 2001 Page 3/5

4 Chemical Resistance: The CS 30 sensor was subjected to the conditions listed in the table below. For reference purposes, each type of test is associated with a number between 1 and 16 (see diagram below) h in tap water 9 1 h in acetone 2 1 h in motor oil 10W-40 at 80 C h in water at 93 C 3 1 h in 2-butanone 11 1 h in xylene 4 1 h in ethanol 12 1 h in pyrrolidone 5 1 h in ethylene glycol 13 1 h in butyl acetate 6 1 h in ethyl acetate 14 1 h in hydrochloric acid 5% 7 1 h in isopropanol h in 1000 ppm ammonia 8 1 h in dipropyl ether h in 1000 ppm chlorine Prior to each test, the sensor was measured in a humidity generator both at 10 %RH and 80 %RH. After each test, the sensor was cleaned for 3 minutes with distilled water in an ultrasonic bath and then dried at 140 C for 25 minutes. Sensor response was measured again in the humidity generator, both at 10 %RH and 80 %RH. Deviation from the original sensor response is reported in the diagram below: 10 %RH 80 %RH Deviation in %RH Type of Test Rotronic July 2001 Page 4/5

5 Evaluation Circuit The following circuit provides a DC voltage signal that corresponds to the raw sensor output. Potentiometer H35 provides an adjustment for tolerances in the sensor nominal capacitance. The output from this circuit can be fed to an amplification circuit (not shown here) with 2 potentiometers (offset and gain) that will be used to adjust / calibrate the signal at two humidity values. Additional circuits may be required for signal linearization and sensor temperature compensation. Rotronic July 2001 Page 5/5