SD Series Dry Cabinets Setup and Operation Manual | A55-7379-00 Rev: 2.0.0 Page 95
Polymer Capacitive Sensor:
The most popular relative humidity electrical sensor, this device actually changes its capacitance as a function
of Relative Humidity, about 0.2pF to 0.5pF per 1%RH. Again, the manufacturer provides details on converting
this capacitance change to %RH. Polymer capacitive sensors are very dependent on the temperature; however
temperature is one of the easiest measurements to take, so this does not present any issues.
Extremely small, this sensor type is well suited for low power, digital humidity and temperature meters often
found in office and factory floor environments.
Typical Polymer capacitive sensor (magnified)
Human Hair Hygrometer (AKA: HHH):
Believe it or not, human hair has the unique property of expanding in high humidity and contracting in low hu-
midity, about 2.5% from 0% to 100%. So a ten-inch long hair will stretch 0.25” from 0% to 100% RH. Though it
is not recommended for measuring humidity in your factory, this method might make a great science fair ex-
hibit project with your school-aged children!
Accuracy:
The readings given by a measurement device are said to be more accurate if there is a small (low) difference
between those readings and the actual value of the parameter being measured. More accuracy is not neces-
sarily gained just because there are a lot of digits in the reading. This just means there is more resolution and
not more accuracy.
Resolution:
This is the total number of significant digits in the measurement value. More resolution is generally considered
better, however, more digits do not equal more accuracy.
Repeatability:
No matter the accuracy or the resolution, when making the same measurement, is the result the same? The
closer the readings of the same measurement are to each other (accurate or not), the better the repeatability.
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