Calibration
For accurate measurements, first calibrate the sensor. You will
need a solution of 1% ethanol in water; to prepare this solution,
pipette in 1.43 mL (or 1.24 g) of 70% ethanol in a 100 mL
volumetric flask and fill to the line with water. The solution should
be at the same temperature as the solutions to be measured.
Calibration data is stored in the sensor’s memory and persists
until the sensor is calibrated again, even if the sensor is
unplugged from the interface.
1. Connect the sensor to an interface as described above.
2. Place the probe above the 1% ethanol solution.
3. Observe the ethanol concentration reading in the software.
4. Wait until the reading stabilizes.
5. Press and hold the 1% CAL button on the sensor for 4
seconds.
Immediately after a successful calibration, the sensor’s output
will read 1%, and the button will be illuminated.
About the Membrane
A roll of membrane material is included with the sensor. The
material is PTFE thread sealing tape, about 25 mm wide,
typically used by plumbers. The membrane protects the sensing
element from liquid, but is permeable to ethanol gas.
Membrane Replacement
Change the membrane when it is torn or discolored.
1. Pull the retaining ring off the end of the probe.
2. Remove and discard the old membrane.
3. Cut a 25 mm square of new membrane material.
4. Place the new membrane over the end of the probe.
5. Push the retaining ring onto the end of the probe over the
new membrane.
6. Optional: Use a sharp knife to trim off excess membrane
from around the retaining ring.
Retaining ring
Old membrane
New membrane
Excess membrane
Factors that Affect the Measurement
Temperature and humidity: The sensor’s temperature is
determined both by its internal heater and the temperature of its
surroundings. Allow the probe time to reach a stable
temperature after you plug it in, or after the temperature of its
surroundings changes. Keep temperature and humidity constant
during calibration and measurement.
Air flow: Air flow around or into the probe affects its
temperature. Minimize air flow during calibration and
measurement.
Interference molecules: In addition to ethanol gas, the sensor
responds to hydrogen, isobutane, carbon monoxide, and
methane.
Sensor Response versus Temperature
The graph below shows how changing temperature affects the
sensor. The probe was placed in the gas above a 1% ethanol
solution and calibrated. The temperature was then varied
between 5° C and 45° C. Though the actual ethanol
concentration of the solution remained constant, the sensor’s
reading deviated from 1% at temperatures above and below the
calibration temperature. This data illustrates the importance of
keeping the temperature constant during calibration and
measurement.
Figure 2. Sensor response vs. temperature; the actual ethanol
concentration is constant
The relationship between temperature and sensor response
varies from probe to probe. To create a similar plot for your
specific probe, follow the steps below.
1. Place the probe and a temperature sensor just above a 1%
ethanol solution. Keep the temperature sensor about 1 cm
away from the heating element at the end of the ethanol
probe. Seal the container to keep the gas in.
2. Calibrate the ethanol sensor at room temperature.
3. Place the container in a cold water bath. Wait for the
temperature inside the container to equilibrate with the
water bath.
4. Start data recording.
5. Use a hot plate to slowly increase the temperature of the
water bath.
Ethanol Sensor | PS-2194
2
