Vernier Software and Technology
Vernier Software & Technology
Tech Info Library

CO2 Gas Sensor Troubleshooting and FAQs

CO2 Gas Sensor, order code CO2-BTA, $269
Specifications and User Guide

Note: There are two types of CO2 Gas Sensors. One model was sold up to about January 2007. The new model was sold after January 2007 and replaces the old model. Specifications for both models are in this article.

-Primary Test: Plug in the sensor, start the data-collection program and allow the sensor to warm up for at least 90 seconds. Blow directly on the shaft of the sensor. You should see an increase in CO2 levels. The older model will max out at 5000 ppm. The newer model will max out at 10,000 ppm if set to the Low Range and 100,000 ppm if set to the High Range (although your breath will probably not reach 100,000 ppm).

-Secondary Test: If the CO2 Gas Sensor is not giving reasonable readings in the Primary Test, try calibrating it. (If you recently blew into the sensor for the Primary Test, wave it around to clear it first.) To calibrate, use a paper clip to press and release the "Cal" button on the sensor. The red LED should begin to flash. (If you hold it so long that it is a solid red, you have reset the factory calibration, which is not what you want to do. If this happens, simply press and release again.) You may have to repeat this two or three times for the CO2 value to adjust to around 400 ppm. (Remember that the accuracy is +/- 100 ppm at this range, so it will not read exactly 400 ppm.) Ideally, this is done in outside air, which is around 400 ppm in unpolluted air, but for a quick test of the sensor, it can be done in inside air. Just don't forget to re-calibrate it in outside air before getting the most accurate values. Note: If the button feels like it's not depressing and the red light does not flash, the button may be stuck under the edge of the plastic. Use the paper clip to free the button and try calibrating again.

-TIL 1519: How to get good results with photosynthesis experiments when using a CO2 Gas Sensor.
-TIL 2318: Can I use a dishwasher to wash the Nalgene bottle that shipped with my O2 or CO2 Gas Sensor?
-TIL 2386: How can I insert a CO2 Gas Sensor or O2 Gas Sensor into my own container?
-TIL 2943: The calibration button on my CO2 Gas Sensor is unresponsive.
-TIL 2957: My CO2 Gas Sensor no longer Auto-IDs.
-TIL 1927: Why does my new CO2 sensor ID as a Current sensor when used with a Go!Link?
-TIL 3351: Do I have an old or current style CO2 sensor?
-TIL 3845: Can CO2 gas concentrations be expressed in units of mg/m^3?
-TIL 4006: What is the volume of gas displaced by the shaft of the CO2 and O2 Gas Sensor? What is the total volume of the Large and Small BioChambers?
-TIL 4339: Can I autoclave the bottle that comes with my CO2 or O2 sensor?

- new order code: CO2-BTA (2007 to present)
- old order code: CO2-DIN/CO2-BTA (prior to 2007)

- Measurement range: 0-5000 ppm CO2 (old model); 1-10,000 ppm and 0-100,000 ppm (new model)
- Accuracy (at standard pressure, 1 atm):
     +/- 100 ppm in the range of 0-1000 ppm
     +/- 10% of reading in the range of 1000-5000 ppm.
- Typical resolution, old model: 20 ppm
- Response time: 95% of full-scale reading in 120 seconds
- Warm-up time (connected to powered interface): 90 seconds
- Output signal range: 0-2.5 V
- Output impedance: 1 kΩ
- Input potential: 5 V (+/- 0.25 V)
- Gas sampling mode: diffusion
- Normal operating temperature range: 25 deg C (+/- 5 deg C)
- Storage temperature range: -40 to 65 deg C

- Accuracy
     +/- 100 ppm or +/- 10% of reading (low range)
     +/- 200 ppm or +/- 20% of reading (high range)
-Typical resolution:
     13-bit resolution (SensorDAQ): 1.5 ppm (low range); 15 ppm (high range)
     12-bit resolution (LabPro, LabQuest, Go! Link, ULI, or SBI): 3 ppm (low range); 30 ppm (high range)
     10-bit resolution (CBL 2): 12 ppm (low range); 120 ppm (high range)
-Response time: 95% of full scale reading in 120 seconds
-Warm up time: 90 seconds
-Pressure effect: 0.19% of reading/mm Hg from standard pressure
-Output signal range: 0-4.0 V
-Input potential: 5 V (+/- 0.25 V)
-Gas sampling mode: diffusion
-Normal operating temperature range: 25 deg C (+/- 5 deg C)
-Operating humidity range: 5-95% (non-condensing)
Storage temperature: -40 to 65 deg C

- Calibrate? Usually no.
- If you do find that you need to calibrate your CO2 Gas Sensor, it can be calibrated using one known CO2 level. Note: This calibration method is different from the usual two-point calibration performed using other Vernier sensors. See the CO2 Gas Sensor Specifications and User Guide for detailed instructions on how to calibrate.

- If you wish to reset the CO2 Gas Sensor to its factory default calibration values (new model only), press and hold the Calibration button for approximately 5 seconds. The red light will change from flashing to steady. When the light turns off, the sensor will be back to its factory settings for that range. This procedure is not the preferred method of calibration due to the fact that the sensor response may have drifted over time. A custom calibration as described above is preferred.

Sensor 'CO2 Gas' (pre-2007)
Calibration 'CO2 ppm':
Equation: Linear
y = bx + a
a: 0
b: 2000
Calibration 'CO2 ppt':
Equation: Linear
y = bx + a
a: 0
b: 2
Calibration 'CO2 %':
Equation: Linear
y = bx + a
a: 0
b: 0.2
Calibration 'CO2 mg/m^3':
Equation: Linear
y = bx + a
a: 0
b: 3551.6

Sensor 'CO2 Gas Sensor'(post-2007)
Calibration 'CO2 Low ppm':
Equation: Linear
y = bx + a
a: 20
b: 2500
Calibration 'CO2 Low ppt':
Equation: Linear
y = bx + a
a: 0.02
b: 2.5
Calibration 'CO2 Low %':
Equation: Linear
y = bx + a
a: 0.002
b: 0.25
Calibration 'CO2 Low mg/m^3':
Equation: Linear
y = bx + a
a: 35.516
b: 4439.5

Calibration 'CO2 High ppm':
Equation: Linear
y = bx + a
a: 20
b: 25000
Calibration 'CO2 High ppt':
Equation: Linear
y = bx + a
a: 0.02
b: 25
Calibration 'CO2 High %':
Equation: Linear
y = bx + a
a: 0.002
b: 2.5
Calibration 'CO2 High mg/m^3':
Equation: Linear
y = bx + a
a: 35.516
b: 44395

250 mL Nalgene Bottle w/Lid, order code CO2-BTL, $5
BioChamber 250, order code BC-250, $8
BioChamber 2000, order code BC-2000, $22

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