Testing Guide For SHTxx Relative Humidity & Temperature Sensor Series Introduction This Qualification Guide defines how Sensirion is testing the various performance parameters of humidity and temperature sensors. Furthermore, it shall help to test and qualify the sensors reliably in due time. It is of great importance that all applicable documents (Datasheet, Users Guide and Handling Instructions) are carefully studied before integration, testing and qualification of the sensor. Testing RH Accuracy Sensor Testing and Qualification It is recommended to run the following test profile: For calibration and end testing of RH sensors Set temperature to 25C (77F) and run a low Sensirion is using expert calibration equipment and medium high RH profile (e.g. 15% 50% 90%) procedures to guarantee highest precision and and check hysteresis with a high medium low reliability. In order to ensure consistent testing of RH profile (e.g. 90% 50% 15%). See also Figure Sensirions SHTxx relative humidity & temperature 1. Allow at least 45 minutes settling time at each sensors the following preparing items should be relative humidity set-point, before starting a carefully considered: measurement. a) Test Objects: The test series should consist of 100% at least 5-10 sensors, which should be taken out of the original packaging. 80% b) Conditioning: Make sure that sensors have not 60% been contaminated prior to the testing. Original 40% packaging should not have been fixed with scotch tape, packaging should not have been 20% stored in plastic bags. If you are unsure 0% whether sensors might have been contaminated or not, follow re-conditioning RH set point profile (%) procedure (80-90C 176-194F at < 5%RH for 24h (baking) followed by 20-30C 70-90F at 0.2% > 74 %RH for 48h (re-hydration). 0.0% -0.2% c) Re-hydration after soldering: In case sensors -0.4% have been soldered to a PCB board please -0.6% make sure that re-hydration procedure (20- -0.8% 30C 70-90F at >74%RH for 48 hours) has -1.0% -1.2% been applied after soldering. -1.4% d) Test set-up: Make sure that test and reference -1.6% sensor experience equal humidity and temperature conditions. If possible apply a RH set point profile (%) professional humidity chamber. If such a Figure 1 Top Panel: Measurement profile for accuracy chamber is not available put the reference and testing (full squares: reference, open diamonds: test test sensor into a closed box and give the set sensor). Lower Panel: RH deviation profile, full line: up time to homogenize. Please make also sure ascending order, hatched line: descending order. that in the humidity housing there are no humidity absorbing materials present near the IMPORTANT: Relative humidity is highly sensors - materials like silicone sealing, rubber, temperature dependent. During the measurement etc. the temperature of reference and test sensor must e) Reference sensor: The reference sensor should show the same value to make RH values be of high reliability. If possible apply a dew comparable. For your test records it is highly point mirror or recently calibrated RH probes. www.sensirion.com Version 1.2 May 2010 1/3 RH Deviation (%) Measured RH (%) 10% 10% 30% 50% 30% 70% 90% 50% 90% 70% 70% 50% 30% 90% 10%RH = 5% Testing Guide for SHTxx Sensors recommended to note RH and T for each set-point 10%RH. Control the temperature carefully as well. and sensor. Then change the air source abruptly and make sure the temperature remains constant. In order to avoid It is also recommended to operate the SHTxx any temperature changes it is recommended to run sensors with EK-H3 or EK-H4 in order to avoid the measurement at ambient temperature. communication or conversion errors. The data should behave roughly inverse Testing RH Response Time exponential see Figure 3. The SHTxx sensors readings shall change 63% of the full RH step within For properly measuring RH response times a test less than 8 seconds. For example if the RH step is set-up shall guarantee a step function from dry air to between 10% and 90% then the RH value shall humid air at the very same temperature, or vice read >60% within 8 seconds. Please note, that for versa. Therefore, the following test set-up is the last few percentages to complete the full step recommended compare with Figure 2. The sensor the response curve will develop with a ilower time is placed into a small box. Across a rotary valve this constant. test chamber shall be fed with dry air taken from compressed, oil-free air and humid air taken There is an alternative option to measure response from a humidity chamber. As the compressed air time in a very simple and effective way which, cools down with expansion, the temperature shall however, may not fulfill scientific standards: Put the be brought to room temperature by a heater. The sensor into a humidity chamber with high humidity heater alternatively can be placed between air bottle (90% for example) or if no humidity chamber is and rotary valve or between rotary valve and test available, put the sensor into a closed box with an chamber. The tubing between the valve and the test open glass of water. Make sure that the chamber shall be kept as short as possible. This temperature inside the chamber or box is equal to allows for an abrupt change from dry to humid air. the outside temperature. Start measuring (for example with the EK-H2 system) and when the values are high and stable immediately quit the Test Compressed air sensor from the box or chamber and expose it to Chamber Humidity the outside conditions. Give the sensor enough time Generator to stabilize the RH value and this way define the full RH step. Now, response time can be derived from the data. RH = 90% T = 20C T = 20C 100% 90% Rotary 80% Valve 70% 60% Exhaust 50% 40% Figure 2 Response time test set up. Dry air from compressed air is blown into test chamber with sensor 30% a heater makes sure the air is at room temperature. With 20% Humidity Setting a rotary valve the relative humidity is taken from a Response Data 10% humidity chamber and therefore abruptly changed from 0% low to high. -10 0 10 20 30 40 50 60 Time (s) To start the measurement blow dry air into the sensor box and give the sensor time to display a Figure 3 Measurement profile of response time testing constant value. It should be in the range of 5 - www.sensirion.com Version 1.2 May 2010 2/3 Relative Humidity (%)