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The 3M Multi-Gas Detector 740 Series is a portable device designed for detecting multiple gases, featuring data logging capabilities and a calibration process to ensure accurate readings.
The primary function of the 3M Multi-Gas Detector 740 Series is to monitor and detect various gases in an environment. It is equipped with sensors for methane (EX), carbon monoxide (CO), and hydrogen sulfide (HS), and also includes an oxygen (OX) sensor. The device is intended for daily usage, with a pre-use sensitivity test mandated by CSA Standard C22.2 No. 152. This test requires checking the detector's sensitivity on a known concentration of the currently selected gas, equivalent to 25-50% LEL (Lower Explosive Limit) of full-scale concentration. The accuracy must be within 0% to 20% of the actual concentration. If the accuracy is outside this range, a calibration of the unit is required. The detector's data logging option allows for the storage and display of calibration dates within a logging session, and it also notes if a bump test has been carried out. This feature helps in maintaining a record of the device's operational status and compliance with safety standards.
The device utilizes a four-gas certified calibration mixture, with methane as the combustible gas. A specific 3M Part Number (933-000-023) is provided for a 34 L cylinder of this mixture. The test gas concentrations can be adjusted at start-up, as detailed in the "Viewing and Changing Settings" video and user instructions. During the sensor test, the gas flow rate for calibration should be maintained between 0.2 and 0.5 liters per minute. The sensor test typically takes 30 seconds, but if values are outside the expected range, a "FULL TEST" is initiated, which can take up to 3 minutes. A full test or calibration can also be invoked by applying gas to the sensors for at least 30 seconds after the conclusion of the initial test.
Before each day's use, a sensitivity test is crucial. The calibration process is initiated by pressing and holding the TEST button for 3 seconds, then releasing it when prompted by the LCD. The LCD will display the days since the last calibration and ask to "ZERO SENSORS?" It is recommended to perform this zero calibration by pressing the POWER/SELECT button. Alternatively, pressing the PEAKS/NO button bypasses the zero calibration, but it's important to note that this also bypasses the oxygen sensor calibration. During the zeroing operation, it's critical to avoid breathing into the detector, as this can affect the oxygen level detected by the OX sensor. After zeroing, the LCD will ask to "TEST SENSORS?" Pressing the POWER/SELECT button initiates the sensor test, while the PEAKS/NO button bypasses it.
During the sensor test, the LCD will display "WAITING FOR GAS" and show the expected gas concentrations for methane (EX), carbon monoxide (CO), and hydrogen sulfide (HS) sensors. An internal timer provides time to connect the certified calibration gas hose. The calibration hood must be placed over the sensors and secured tightly with a retaining screw. A hose from the correct calibration gas bottle is then attached to the gas inlet of the detector, and the valve is turned on, ensuring the correct gas flow rate. The LCD will then change to "TESTING." Upon successful completion, the LCD will read "TEST PASSED" or "FULL TEST PASSED." After a successful test, the gas valve should be turned off, and the hose disconnected. If the test is unsuccessful, the LCD will read "SENSOR TEST FAILED," and it is recommended to repeat the test. If the detector fails the second test, it should not be used until the reason for the failure is determined and corrected. Troubleshooting information is available in the user instructions or by contacting 3M Technical Service.
Calibration of the unit is recommended every 30 days or immediately if it fails the bump test. Factors such as sensor age and exposure to high gas concentrations may necessitate more frequent calibration. The data logging feature assists in tracking calibration dates and bump test results, aiding in scheduled maintenance. The zeroing operation is a key part of maintenance, ensuring the sensors are reset to a baseline. If the detector consistently fails tests, it indicates a need for troubleshooting, which can be done by consulting the user instructions or contacting 3M Technical Service. Regular calibration and adherence to the daily sensitivity test protocol are essential for maintaining the accuracy and reliability of the 3M Multi-Gas Detector 740 Series.
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