3M ™ Multi-Gas Detector 740 Series with Data Logging
Software – Calibration
Calibration of the unit should be performed every 30 days or immediately if it does not
pass the bump test. Factors such as age of the sensor and exposures to very high
concentrations of gas may require the sensor to be calibrated more frequently.
The data logging option for the detector allows for storage and display of the calibration
dates with a logging session, and makes a notation if a bump test has been carried out.
CAUTION – CSA Standard C22.2 No. 152 states that before each day’s usage
sensitivity must be tested on a known concentration of the currently selected gas
equivalent to 25-50% LEL of full scale concentration. Accuracy must be within 0%
- 20% of the actual. Accuracy may be corrected by performing a calibration of the
unit.
To calibrate the detector:
a)
Go to a non-contaminated environment to perform the calibration.
b)
Turn on the unit and allow it to warm up.
c)
Choose the appropriate certified gas by matching the sensors with the gas
mixtures noted in the user instructions.
NOTE:
A four-gas certified calibration mixture is available from 3M using
methane as the combustible gas (
3M Part Number 933-000-023
in a 34 L
cylinder). Test gas concentrations can be changed by changing the test
concentration at start up (shown in the “Viewing and Changing Settings”
Video). See the user instructions for more information.
d)
Press and hold the TEST button for 3 seconds while observing the LCD,
release the button when indicated by the LCD.
e)
The LCD will then display the days since the sensors were last calibrated and
ask if you wish to “ZERO SENSORS?” It is recommended that you do so.
f)
Press the POWER/SELECT button to accept the zero calibration.
g)
Press the PEAKS/NO button if you wish to by-pass a zero calibration, note
that this will bypass the oxygen sensor calibration.
h)
The oxygen sensor is calibrated during the zeroing operation so avoid
breathing into the detector during this operation as you could affect the
oxygen level being detected by the OX sensor.
i)
At the conclusion of the zeroing step, the LCD will ask if you wish to “TEST
SENSORS?”
