27904 Parallax Inc, 27904 Datasheet - Page 4

• Manufacturer Part Number: 27904
• Description: ALCOHOL BENZINE GAS SENSOR
• Manufacturer: Parallax Inc

Specifications of 27904

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Calibration
The procedure for setting these potentiometers is explained below.
potentiometer clockwise decreases voltage, while turning the potentiometer counter-clockwise increases
it. This can be compared to a water valve.
The gas sensor module’s ALR pin should only be checked when the heater is on and the readings have
stabilized.
Note: Temperature and humidity are factors that could affect the sensor, making calibration difficult. If
this should happen try adjusting the voltages used in the calibration up or down as necessary to find a
more stable range.
Copyright © Parallax Inc.
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For the CO sensor, please read the CO Sensor Specifics on page 5 before attempting calibration.
Place the Gas Sensor Module in a clean air environment and supply power to the module. The
heater should be active during this time. Allow at least 10 minutes before making adjustments.
Adjust potentiometer R4 until the voltage across TP3 (+) and TP4 (-) reads approximately
0.80 V.
Adjust potentiometer R3 until the voltage across TP1 (+) and TP2 (-) reads approximately
At this point adjusting R3 up/down should make the LED toggle on/off. Adjust R3 so the LED
just goes off.
Apply your gas source to the gas sensor. The LED should light up.
Remove the gas source and allow the sensor to settle. The LED should go back out.
If the LED does not go out within 60 seconds, adjust R3 until the LED goes out and repeat the
two previous steps.
0.80 V.
Gas Sensor Modules (#27930, #27931, #27932, #27904) v2.2 8/2/2010 Page 4 of 6
Please note that turning the