Electricity and Control May 2020

PLANT MAINTENANCE, TEST + MEASUREMENT

At a glance ■  Most manufacturers of gas monitors recommend that the monitors should be bump tested prior to each day’s use and calibrated at least monthly. ■  In two extensive studies, Industrial Scientific investigated whether or not such recommendations are followed in the field, and the levels of risk resulting from actual testing practices. ■ The challenges of safety and maintenance of current gas monitors can be overcome by incorporating sensor redundancy in monitors.

This confirms that the monitor with DualSense Technology is much safer than a traditional single gas monitor, irrespective of bump test schedule, on average 85 times safer. Even in the extreme comparison of a traditional monitor bump tested every day, versus a monitor with DualSense Technology bump tested every month, the monitor with DualSense Technology is 17 times safer than a traditional monitor. Incorporating DualSense Technology is a cost-effective means to improve safety of gas monitors significantly in real world conditions – conditions where it might not be possible to perform a bump test before each day’s use. DualSense Technology provides the user with a number of other benefits. The ready availability of working gas monitors is a critical factor in keeping production lines and drilling rigs, for example, working. Without working monitors, productivity can decline, costs can increase with the need for backup instruments, or at worst – a user goes into the field to work with no instrument at all. A redundant sensor provides a short-term solution when one sensor fails for people to still be able to go out and do their jobs, though overall safety must be maintained by performing more frequent bump tests. An analogy may be drawn to a spare tyre in a car. It is a valuable backup and means the car is available to drive although it must be driven with some constraints – at a slower speed and for a short distance. □

DualSense Technology, together with a daily self-check that verifies proper operation of the electronics and alarms, makes for a much safer and more cost-effective monitor.

An alternative technology The majority of failures in gas detectors are due to sensor failures. All major manufacturers of gas monitor sensors use similar technologies, mostly electrochemical sensors (used to detect H 2 S, CO, O 2 , and other gases) or catalytic bead sensors for explosive gas detection. These sensors have been in use for years and are well understood. They are simple, cheap and reasonably reliable as long as regular bump tests are performed. While newer sensors with cutting edge technology seem perpetually on the horizon promising significant benefits, the ready availability and cost effectiveness of traditional electrochemical and catalytic sensors make them the mainstay of the industry. DualSense Technology TM exploits the ready availability and cheap price of traditional sensors by adding sensor redundancy to overcome the safety and maintenance challenges of current gas monitors. The two sensors sense the same gas and provide simultaneous readings to the monitor’s electronics which apply a proprietary algorithm to calculate and display a single reading. DualSense Technology, together with a daily self-check that verifies proper operation of the monitor electronics and alarms, makes for a much safer and more cost- effective monitor. How much safer is a user of a single gas monitor with DualSense Technology than a user of a traditional single gas monitor with a single sensor? Using the data on failure rates presented above, the failure rate for DualSense- based monitors can be calculated. Figure 3 shows the comparative safety of the two types of monitors in terms of average instrument use days before failure. For both monitors – those with DualSense Technology and those with a single sensor – where they are bump tested before each day’s use, one failure in over 300 years can be expected for the instrument with DualSense Technology, compared to one failure in 3.5 years for the traditional instrument. If the monitors were bump tested every month, on average the failure rate of the instrument with DualSense Technology is one failure in just under six years, compared to one failure in 286 days for traditional gas monitors.

Comtest, leading local distributor of test and measurement instrumentation to industry represents Industrial Scientific (ISC) in South Africa. ISC, a leading global provider of gas solutions, develops, manufactures and services fixed and portable gas detection equipment for utilities and a wide range of industries. It provides gas monitors for remote sampling, detecting atmospheric hazards in confined spaces, area monitoring, or personal protection.

For more information visit: https://comtest.co.za

Electricity + Control MAY 2020

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