SI7015-A20 Datasheet, PDF (13/39 Pages) Silicon Laboratories – DIGITAL IC HUMIDITY AND TEMPERATURE SENSOR

Si7015-A20
4.2. Relative Humidity Sensor Accuracy
To determine the accuracy of a relative humidity sensor, it is placed in a temperature and humidity controlled
chamber. The temperature is set to a convenient fixed value (typically 30 °C) and the relative humidity is swept
from 20 to 80% and back to 20% in the following steps: 20% – 40% – 60% – 80% – 80% – 60% – 40% – 20%. At
each set-point, the chamber is allowed to settle for a period of 60 minutes before a reading is taken from the
sensor. Prior to the sweep, the device is allowed to stabilize to 50%RH. The solid top and bottom trace in Figure 6,
“Measuring Sensor Accuracy Including Hysteresis,” shows the result of a typical sweep after non-linearity
compensation.
RHAccuracyvs.RHSetͲPoint
5
4

3
Hysteresis
2
1
0
Ͳ1
10
20
30
40
50
60
70
80
90
Ͳ2
Ͳ3
Ͳ4
Ͳ5
%RHSetͲpoint
Figure 6. Measuring Sensor Accuracy Including Hysteresis
The RH accuracy is defined as the center (dashed) line shown in Figure 6, which is the average of the two data
points at each relative humidity set-point. In this case, the sensor shows an accuracy of 0.25%RH. The Si7015
accuracy specification (Table 4) includes the following:
Unit-to-unit and lot-to-lot variation in non-linearity compensation
Accuracy of factory calibration
Margin for shifts that can occur during solder reflow.
The accuracy specification does not include the following:
Hysteresis (typically ±1%)
Effects from long term exposure to very humid conditions
Contamination of the sensor by particulates, chemicals, etc.
Other aging related shifts (“Long-term stability”)
Variations due to temperature
Rev. 1.0
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