Extech Instruments CO240 User Manual

4 CO240-en-US_v1.9 10/22
Auto Power Off
The CO240 will automatically turn off after 20 minutes of inactivity. To disable the auto power
off function: With the meter OFF, press and hold the HOLD button and then press the POWER
button. The LCD will show “n”, and will then return to normal measurement mode.
Measurements
When the meter is turned on, a self-test is implemented. Due to the nature of the NDIR sensor,
it typically requires approximately ten minutes to obtain stable, accurate readings. If the USB
cable is connected to the CO240, the USB symbol will be shown on the LCD.
The temperature and relative humidity readings will alternate on the lower LCD line along with
the CO
2
reading on the top display line. Use the MODE button to switch to DP (Dew Point
Temperature) and WB (Wet Bulb Temperature) modes (lower display line).
Maximum and Minimum Readings Memory
Momentarily press the MAX/MIN button to review the maximum and minimum readings
captured since the meter was powered on. Pressing the button once will show the maximum
value. Pressing the button again will display the minimum value. Pressing the button a third time
will return the meter to its normal mode of operation. While in MAX-MIN mode, press and hold
the HOLD button for 2 seconds to reset (clear) the stored maximum and minimum values.
Selecting
o
C/
o
F units of measure
Press the UNIT button to select the desired temperature unit of measure.
Calibration
Press and hold the SET + UNIT buttons for 2 seconds to enter the self-calibration mode. Ensure
that there is as little CO
2
present as possible. It is recommended that this be done in outside air.
The LCD will display “CAL” and will perform a 60-second countdown as it performs the
calibration. A reading of “400” is displayed as a normal CO
2
level reference value during the
calibration. After the calibration has completed, the meter will return to its normal mode
operation.
Automatic CO
2
Baseline Calibration (ABC)
The ABC algorithm continually tracks the sensor’s lowest reading over a fixed time interval and
slowly corrects for any long-term drift (as compared to the expected fresh air value of 400ppm).
The ABC period is 15 days, during which the ABC function default is always on.

Extech Instruments CO240 Specifications

Display and Measurement

display	Dual multifunction LCD
CO2 measure range	0 to 9, 999 ppm
CO2 accuracy	± (75 ppm + 5% of reading) 0 to 2, 000 ppm

Operating Environment

operating temperature	0 to 50°C (32 to 122°F); 0.1° resolution
operating relative humidity	0 to 95% RH (avoid condensation)
relative humidity accuracy	± 5% of rdg at 25°C (77°F) otherwise ±7% RH

Temperature Ranges

dew point temperature range	‐72.9 to 47°C (‐99.22 to 118°F); 0.1° resolution
wet bulb temperature range	‐11 to 48.2°C (12.2 to 118.8°F); 0.1° resolution
temperature accuracy	± 1°C (1.8 °F)

Storage Conditions

storage temperature	‐20 to 50°C (‐4 to 122°F)
storage humidity	0 to 95% RH (avoid condensation)
dimensions	211 x 60 x 40 mm (8.3 x 2.4 x 1.6")

Power and Weight

power	AAA batteries x 6 pcs or AC adaptor
weight	181.4 g (6.4 oz.)