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How the Relative Humidity Sensor Works
The heart of this sensor is the Hy-Cal Engineering IH-3602-L Integrated Circuit
Humidity Sensor, which uses a capacitive polymer to sense humidity. An integrated
circuit then produces an output voltage which varies with relative humidity. The
response time of the unit in moving air is much shorter than in still air. In some
cases, you may want to create air currents (by moving the sensor or using a fan) to
speed up the response of the sensor.
The sensor is slightly light sensitive. The housing is designed to minimize the
amount of light that can penetrate the sensor opening. The calibration of the sensor is
somewhat affected by temperature. This effect is negligible at the low relative
humidity readings, but increases at high humidities. If you want to correct for this
error, you can create different calibration files for different temperatures. In most
cases, this is unnecessary.
This sensor is equipped with circuitry that supports auto-ID. When used with
LabQuest 2, LabQuest, LabQuest Mini, LabPro, Go! Link, SensorDAQ, EasyLink,
TI-Nspire™ Lab Cradle, or CBL 2™, the data-collection software identifies the
sensor and uses pre-defined parameters to configure an experiment appropriate to the
recognized sensor.
Optional Calibration Procedure
You do not need to perform a new calibration on the Relative Humidity Sensor. We
have set each Relative Humidity Sensor to match the stored calibration before
shipping it. You can simply use the appropriate calibration file that is stored in your
data-collection program from Vernier.
For greatest accuracy, this Relative Humidity Sensor can be calibrated. Calibration
can be done by comparison to another instrument that measures relative humidity
(hygrometer or psychrometer). Another way is to use salt solutions. You would do a
two-point calibration as you probably have done with other sensors such as pH
sensors. The salt solutions are used to maintain environments with different known
relative humidities. If you place moist salts in a sealed container, the air above it will
reach a known relative humidity. A table of values is shown on the next page. The
relative humidity above the salt depends slightly on the temperature, so the table also
lists temperature.
Here is a step-by-step procedure,
1. Place a handful of salt in the bottom of a jar (quart or liter size is fine).
2. Add a little water to the jar so that the salt is wet. The goal is to end up with wet
salt, not to totally dissolve the salt.
3. Place the Relative Humidity Sensor in a jar. Do not get the salt or salt solution on
the sensor.
4. Seal the jar. We usually use plastic wrap and rubber bands.
5. Start the program and allow some time (2 to 6 hours) for the air inside the sensor
to reach the proper relative humidity level.
6. Go through the procedure for the first point of calibration. Type in the relative
humidity for the salt you used, as determined from the table.
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7. Repeat the procedure for the second calibration point using a different salt. Be
sure to allow enough time for the Relative Humidity Sensor to adjust for the
change in humidity.
Even though none of the salts listed here is especially dangerous, use normal
precautions with these chemicals.
Here are the relative humidity readings to use when calibrating with salts. These
numbers were taken from Hy-Cal Engineering IH-3602-L data sheets.
All Data in %
15°C 20°C 25°C 30°C 35°C
Lithium
Bromide
6.86 6.61 6.37 6.16 5.97
Lithium
Chloride
11.3 11.31 11.3 11.28 11.25
Potassium Acetate
23.40 23.11 22.51 21.61 -
Magnesium Chloride
33.3
33.07 32.78 32.44 32.05
Potassium Carbonate
43.15 43.16 43.16 43.17 -
Magnesium Nitrate
55.87
54.38 52.89 51.4 49.91
Potassium Iodide
70.98
69.90 68.86 67.89 66.96
Sodium
Chloride
75.61 75.47 75.29 75.09 74.87
Ammonium Sulfate
81.70
81.34 80.99 80.63 80.27
Potassium Chloride
85.92
85.11 84.34 83.62 82.95
Potassium
Nitrate
95.41 94.62 93.58 92.31 90.79
Warranty
Vernier warrants this product to be free from defects in materials and workmanship for a
period of five years from the date of shipment to the customer. This warranty does not
cover damage to the product caused by abuse or improper use.
Vernier Software & Technology
13979 S.W. Millikan Way
Beaverton, OR 97005-2886
Toll Free (888) 837-6437
(503) 277-2299
FAX (503) 277-2440
www.vernier.com
Rev 6/5/2012
Logger
Pro
, Logger Lite, Vernier LabQuest 2, Vernier LabQuest, Vernier LabQuest Mini, Vernier LabPro, Go! Link,
Vernier EasyLink and other marks shown are our trademarks or registered trademarks in the United States.
TI-Nspire, CBL 2 and CBL, TI-GRAPH LINK, and TI Connect are trademarks of Texas Instruments.
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