The electrochemical sensor has been a vital device in ensuring workplace safety, and protecting lives, for over five decades. The electrochemical sensor was used for oxygen monitoring for the first time in the 1950s. Over the years, the expansion of the technology made the sensor a key component in the determination and monitoring of toxic gases.
In the 1980s, the Occupational Safety and Health Administration (OSHA) announced a proposal for a new safety standard, which would demand toxic gas monitoring in permit-required confined spaces. This announcement triggered the development of more compact and powerful electrochemical sensors with improved sensitivity and selectivity for a broad range of toxic gases.
The proposed OSHA safety standard came into effect in 1993 as 29 CFR 1910.146, mandating rigorous worker safety and further widening the scope of application of the electrochemical sensor.
Detcon’s Electrochemical Toxic Gas Sensors
The simplest form of all electrochemical gas detection sensors consists of a porous membrane and at least two electrodes, namely a sensing electrode and a counter electrode. During operation, the gas permeable sensor membrane allows the target gas to diffuse through it onto the surface of the sensor electrode. This generates an electrical current proportional to the quantity of target gas reacted at the electrode.
Electrochemical toxic gas sensors offered by 3M Gas & Flame Detection include three electrodes embedded in an electrolyte solution and placed in a diffusion membrane (Figure 1). Sensitivity to a specific target gas is achievable by changing the composition of any combination of the sensor components. These sensors have long service life of three or more years because the cells are diffusion limited by tiny capillary barriers.
Figure 1. Detcon’s electrochemical toxic gas sensor
Detcon’s electrochemical sensors are rugged, perform well at elevated temperatures and in challenging environments, and can determine toxic gases ranging from 0-1 ppm up to 0-10,000 ppm. 3M Gas & Flame Detection produces six sensor assemblies for toxic gas monitoring using this electrochemical cell technology.
MicroSafe® Models DM-500/600, Model DM-100, SmartWireless® Models CX/CXT-DM, and Model DM-700 are user-friendly field replaceable plug-in sensors with smart electronics and a non-intrusive operator interface that uses a hand-held magnet. These intuitive sensors feature comprehensive fault diagnostics and automatic calibration.
DM-100 2-Wire Loop-Powered
The Model DM-100 (Figure 2) features two-wire 4-20 mA loop-powered sensors packaged in an electro-polished 316 stainless steel vault. This versatile, low power gas detector has a safe design with fully encapsulated electronics. An explosion-proof junction box, with or without loop powered LED display, is available as one of options. The DM-100 is rated Class I, Division I, Groups A, B, C, D and ATEX approved as II1G Ex ia IIC T4 Ga and as II26 Ex mb [ib] ib IIC T4 Gb.
Figure 2. The Model DM-100
DM-700 Environmentally Bulletproof
The Model DM-700 (Figure 3) comes as standard with 4-20 mA and Modbus RS-485 outputs. Designed for harsh environments, this new generation of intelligent sensor module is packaged in an intrinsically safe electro-polished 316 stainless steel vault with dual layer surge protection and fully encapsulated electronics. An integrated alphanumeric LED display shows the sensor status.
Figure 3. The Model DM-700
The DM-700 contains an explosion-proof junction box, and is Class I, Division I, Groups A, B, C, D and ATEX approved as II 2G Ex d ib IIC T4 Gb. The sensor module has a SIL2 rating assessed by Exida. Integration options are a wireless interface module, HART, and Remote Alarm Module (RAM).
Models DM-500 and DM-600 MicroSafe gas detectors (Figure 4) are equipped standard with a linear 4-20 mA output. An additional RS-485 serial communications port and three alarm relays are featured in the DM-600. Both sensor types can be purchased with a remote sensor and remote transmitter option. They are rated Class I, Division I, Groups B, C, D and are housed in explosion-proof junction boxes with a glass lens cover.
Figure 4. Detcon Models DM-500 and DM-600 MicroSafe gas detectors
SmartWireless CX-DM and CXT-DM gas detectors (Figure 5) can be deployed easily in both temporary and permanent installations. They are advanced, low-power field devices with rating of Class I, Division I, Groups C, D.
Figure 5. Detcon’s SmartWireless CX-DM and CXT-DM gas detectors
The CXT model consists of a low power sensor and wireless transceiver housed in a single enclosure. Power is supplied by means of rechargeable or disposable battery options. The CX model comes with standard analog 4-20 mA and Modbus RTU RS-485 outputs. It is possible to use both CX-DM and CXT-DM as components of the transportable Site Sentinel gas detection system.
This information has been sourced, reviewed and adapted from materials provided by 3M Gas & Flame Detection.
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