Vernier Software and Technology
Vernier Software & Technology

Go Direct® CO2 Gas Sensor User Manual

Go Direct® CO2 Gas Sensor

Go Direct CO2 Gas measures carbon dioxide concentration, temperature, and relative humidity. This sensor includes built-in temperature compensation and humidity protection. A 250 mL Nalgene bottle is included for running controlled experiments with small plants and animals.

Go Direct CO2 Gas is ideal for the following experiments:

  • Measure the change in CO2 gas concentration during cellular respiration.
  • Measure the change in CO2 gas concentration during photosynthesis.
  • Study the effect of temperature on cell respiration or metabolism of organisms.
  • Study how yeast metabolize different sugars.
  • Investigate artificial selection by comparing respiration rates of different yeast strains.

Note: Vernier products are designed for educational use. Our products are not designed nor are they recommended for any industrial, medical, or commercial process such as life support, patient diagnosis, control of a manufacturing process, or industrial testing of any kind.

What's Included

  • Go Direct CO2 Gas
  • Micro USB Cable
  • 250 mL Nalgene Bottle w/Lid

Compatible Software

Getting Started

Please see the following link for platform-specific connection information:

Bluetooth Connection

USB Connection

  1. Install Graphical Analysis 4 on your computer, Chromebook™, or mobile device. If using LabQuest 2, make sure LabQuest App is up to date. See for Graphical Analysis 4 availability or to update LabQuest App.
  2. Charge your sensor for at least 2 hours before first use.
  3. Turn on your sensor by pressing the power button once. The LED will blink red.
  4. Launch Graphical Analysis 4 or turn on LabQuest 2.
  5. If using Graphical Analysis 4, click or tap Sensor Data Collection. If using LabQuest 2, choose Wireless Device Setup > Go Direct from the Sensors menu.
  6. Select your Go Direct sensor from the list of Discovered Wireless Devices. Your sensor's ID is located near the barcode on the sensor. The LED will blink green when it is successfully connected.
  7. Click or tap Done. You are now ready to collect data.
  8. This is a multi-channel sensor. To change the channel selections, see
  1. If using a computer or Chromebook, install Graphical Analysis 4. If using LabQuest 2, make sure LabQuest App is up to date. See for Graphical Analysis 4 availability or to update LabQuest App.
  2. Connect the sensor to the USB port.
  3. Launch Graphical Analysis 4 or turn on LabQuest 2. You are now ready to collect data.
  4. This is a multi-channel sensor. To change the channel selections, see

Charging the Sensor

Connect Go Direct CO2 Gas to the included Micro USB Cable and any USB device for two hours.

You can also charge up to eight Go Direct CO2 Gas Sensors using our Go Direct Charge Station, sold separately (order code: GDX-CRG). An LED on each Go Direct CO2 Gas indicates charging status.


Blue LED on steady while sensor is connected to the Micro USB Cable or Charge Station.

Fully charged

Blue LED is off when charging is complete.

Powering the Sensor

Turning on the sensor

Press button once. Red LED indicator flashes when unit is on.

Putting the sensor in sleep mode

Press and hold button for more than three seconds to put into sleep mode. Red LED indicator stops flashing when sleeping.

Connecting the Sensor

See the following link for up-to-date connection information:

Connected and charging Blue and Green LED solid when sensor is connected to Graphical Analysis via USB and unit is charging. (Green LED is obscured by the blue one.)
Connected, fully charged Green LED solid when sensor is connected to Graphical Analysis via USB and the unit is fully charged.
Charging via USB,
connected via Bluetooth
Blue LED is solid and green LED is flashing, but the green flashing LED looks white because it is overwhelmed by the blue.

Identifying the Sensor

When two or more sensors are connected, the sensors can be identified by tapping or clicking Identify in Sensor Information.

Using the Product

Connect the sensor following the steps in the Getting Started section of this user manual.


Go Direct CO2 Gas has three measurement channels:

  • CO2 Gas
  • Temperature
  • Relative Humidity

CO2 Gas

This channel measures the carbon dioxide concentration in the air. Units can be changed from parts per million (ppm) to parts per thousand (ppt), percent (%), or mg/m3. See for more information. The readings are temperature compensated regardless of whether the temperature channel is activated. This is the default channel that is active when the sensor is connected.


This channel measures air temperature inside the sensor. Units can be changed from °C to °F or K. This channel is not active by default when the sensor is connected.

Relative Humidity

This channel measures the relative humidity of the air. It is not used to compensate CO2 gas readings. This channel is not active by default when the sensor is connected.


Calibrating the Sensor

CO2 Gas

The CO2 Gas sensor is factory calibrated. For many experiments, it will not be necessary to calibrate this sensor when using this channel. However, for best accuracy, the sensor can be calibrated using a one-point calibration based on a sample of outside air. Atmospheric air typically has a carbon dioxide concentration of around 400 ppm. Actual levels in your area may be slightly higher due to localized influences such as automobile or industrial emissions of carbon dioxide. To calibrate Go Direct CO2 Gas

  1. Fill the 250 mL Nalgene bottle to the brim with water, take it outside, and dump the water to ensure it is then filled with fresh air. While still outdoors, insert the sensor into the gas sampling bottle that now contains fresh outside air. Take the bottle and sensor to where the calibration will be done.
  2. Start the software and identify your sensor, if necessary. Let the sensor warm up for at least 180 seconds before continuing.
  3. When the sensor has warmed up (readings should have stabilized), calibrate the sensor using a one-point calibration. Enter a value of 400 ppm for the sample of air collected. Once finished, the sensor should read very close to 400 ppm.


The temperature sensor is factory calibrated and cannot be calibrated by the user.


The relative humidity sensor is factory calibrated and cannot be calibrated by the user.


CO2 Sensor




0–100,000 ppm


0 to 1,000 ppm ±100 ppm

1,000 to 10,000 ppm ±5% of reading +100 ppm

10,000 to 50,000 ppm ±10% of reading

50,000 to 100,000 ppm ±15% of reading


1 ppm CO2

Warm-up time

180 seconds

Gas sampling mode


Temperature Sensor







Relative Humidity Sensor




0 to 100% (non-condensing)


±5% or better



USB specification


Wireless specification

Bluetooth 4.2

Maximum wireless range

30 m unobstructed


650 mA Li-Poly

Battery life (single full charge)

~8 hours

Battery life (long term)

~500 full charge cycles (several years depending on usage)

Normal operating temperature range

20 to 40°C

Operating humidity range

5 to 95% (non-condensing)


Sensor tube: 82 mm length, 28 mm OD; total length: 200 mm

Care and Maintenance

Battery Information

Go Direct CO2 Gas contains a small lithium-ion battery. The system is designed to consume very little power and not put heavy demands on the battery. Although the battery is warranted for one year, the expected battery life should be several years. Replacement batteries are available from Vernier (order code: GDX-BAT-650).

Storage and Maintenance

To store Go Direct CO2 Gas for extended periods of time, put the device in sleep mode by holding the button down for at least three seconds. The red LED will stop flashing to show that the unit is in sleep mode. Over several months, the battery will discharge but will not be damaged. After such storage, charge the device for a few hours, and the unit will be ready to use.

Exposing the sensor to temperatures below –15°C or over 45°C will damage the sensor. Additionally, temperatures over 35°C (95°F) will reduce the battery's lifespan. If possible, store the device in an area that is not exposed to temperature extremes.

Note: It is recommended that you wash the Nalgene bottle by hand. Most dishwashers will melt plastic bottles.

Water Resistance

Important: Go Direct CO2 Gas is neither waterproof, nor is it water resistant, and should never be immersed in water.

If any liquid gets into the device, immediately power the unit down (press and hold the power button for more than three seconds). Disconnect the sensor and charging cable, and remove the battery. Allow the device to dry thoroughly before attempting to use the device again. Do not attempt to dry using an external heat source.

Note: Damage due to liquid is not covered under warranty.

How the Sensor Works

Go Direct CO2 Gas measures gaseous carbon dioxide levels in the range of 0 to 100,000 ppm by monitoring the amount of infrared radiation absorbed by carbon dioxide molecules. Carbon dioxide gas moves in and out of the sensor tube by diffusion through the vent holes in the sensor tube. The sensor uses a small light to generate infrared radiation (IR). The IR source is located at one end of the sensor’s shaft. At the other end of the shaft is an infrared sensor that measures how much radiation gets through the sample without being absorbed by the carbon dioxide molecules. The detector measures infrared radiation in the narrow band centered at 4260 nm. The greater the concentration of the CO2 gas in the sampling tube, the less radiation will make it from the source through the sensor tube to the IR detector.

The sensor also measures air temperature in the sensor shaft using a thermistor in an integrated circuit. When the temperature increases, the resistance of the thermistor decreases. The circuit measures the resistance value at a particular temperature and converts this to a digital signal.

Relative humidity is measured in the sensor shaft using an integrated circuit that uses a capacitive polymer to sense humidity. The circuit produces a signal which varies with relative humidity.


  • Very important: Do not place the sensor into any liquid. The sensor is intended only for measuring gaseous, not aqueous, CO2 concentration.
  • Allow the sensor to warm up for at least 180 seconds before use. The warm-up process begins when the sensor is charging, connected to a USB port, or connected to software via Bluetooth wireless technology.
  • The sensor is sensitive to high humidity. Do not use in a condensing environment.
  • The sensor has built-in temperature compensation but the sensor can still be sensitive to rapid and/or large changes in temperature. The sensor is designed to operate best between 20 and 40°C. This does not prohibit the sensor from being used in temperatures outside this range. Just allow enough time for the sensor to stabilize at the desired air temperature. For more accurate results, the sensor can be calibrated at the temperature used.
  • The recommended sampling rate is 0.5 samples per second or slower for this sensor. This allows the sensor to average a set of measurements before reporting a value. Gas must diffuse through the holes in the sensor tube before the sensor detects any changes in concentration. Because diffusion of gases is a slow process, there can be a delay in response time.
  • To collect data in a controlled environment, it is recommended that you use the 250 mL Nalgene bottle that is included with this sensor.
  • To collect data simultaneously with Go Direct CO2 Gas and Go Direct O2 Gas, it is recommended that you purchase either the BioChamber 250 (250 mL capacity) or the BioChamber 2000 (2 L capacity). Each BioChamber has a second opening with a grommet so that you can insert two probes at once.
  • Because the sensor operates on the basis of reading IR radiation, you should avoid using the sensor in direct sunlight as much as possible. Even though the IR detector is shielded, it is best to avoid the possibility of reflected light affecting the readings by keeping the sensor in the shade when used outdoors.
  • If the reported CO2 gas concentration appears to be incorrect (after the 180 second warm up), calibrate the sensor as described in the Calibration section. Keep in mind that indoor CO2 gas concentration can vary a great deal and that there can be unit to unit variability of up to 200 ppm CO2 between sensors.
  • If the sensor is reading at or near the maximum range of the sensor, the CO2 concentration may be exceeding the maximum range of the sensor. Place the sensor in outside air or in ambient room air and wait for the readings to decrease.
  • If there is no change in CO2 gas concentration during an experiment, it may be the experiment and not the sensor. Test the sensor by removing it from the reaction chamber and gently blowing on the shaft to see if it responds to exhaled air.

For more troubleshooting and FAQs, see

Repair Information

If you have followed the troubleshooting steps and are still having trouble with your Go Direct CO2 Gas, contact Vernier Technical Support at or call 888-837-6437. Support specialists will work with you to determine if the unit needs to be sent in for repair. At that time, a Return Merchandise Authorization (RMA) number will be issued and instructions will be communicated on how to return the unit for repair.



Vernier warrants this sensor to be free from defects in materials and workmanship for a period of five years from the date of shipment to the customer (bottle and lid are excluded). This warranty does not cover damage to the product caused by abuse or improper use. This warranty covers educational institutions only.


When disposing of this electronic product, do not treat it as household waste. Its disposal is subject to regulations that vary by country and region. This item should be given to an applicable collection point for the recycling of electrical and electronic equipment. By ensuring that this product is disposed of correctly, you help prevent potential negative consequences on human health or on the environment. The recycling of materials will help to conserve natural resources. For more detailed information about recycling this product, contact your local city office or your disposal service.

Battery recycling information is available at

Do not puncture or expose the battery to excessive heat or flame.

The symbol, shown here, indicates that this product must not be disposed of in a standard waste container.

Contact Support

Fill out our online support form or call us toll-free at 1-888-837-6437.

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