GDS   GMII-00-000-00/01-061-05/0-0

Inquiry

The GASMAX II gas monitor for VOCs uses a photoionization detector (PID) to detect concentrations of volatile organic compounds (VOC) such as benzene, toluene, xylene and chlorinated hydrocarbons.

The PID Smart Sensor is available in High Range (0-300 ppm) and Low Range (0-50 ppm) for maximum flexibility. The PID sensor is fitted with replaceable 10.6 eV or 9.6 eV source lamps designed to ionize the most commonly found VOCs while remaining insensitive to changes in humidity, oxygen or CO2 levels. Any compound with an ionization potential lower than the lamp value can be detected with the GASMAX II / PID monitor.

Built-in dual channel electronics allow the GASMAX II to support any GDS Corp oxygen or toxic gas sensor in combination with the photoionization detector.

The highly visible backlit display and high intensity alarm LEDs constantly show alarm status, gas reading and programmable tag name; a second screen shows alarm levels and the most recent 30 minute trend. An internal real-time clock and event log time-stamp calibration and alarm events for later review. A menudriven operator interface using magnetic keys eliminates all analog potentiometers and allows complete setup and calibration without hazardous area declassification.

In addition to standard dual 4-20mA current loop outputs, an optional dual isolated 4-20mA output board or an RS-485 2-wire MODBUS® interface with three 5A SPDT relays are available to communicate with controllers or drive local alarm indicators. When used with the C1 Protector Controller’s MODBUS master port, multiple GASMAX II monitors can be daisy-chained up to 500m.

Available in both single and dual channel models, the GASMAX II is CSA certified for use in Class I, Div 1 explosion proof installations. For low temperature applications, an Extended Temp option adds thermostatically controlled heaters to enable operation as low as –55°C ambient for electrochemical sensors.

• CSA Certified for Class I, Div 1 explosion-proof installations
• Monitor both toxic gases and VOCs with one detector
• Graphic display shows values, units, trend graph, alarm levels
• Supports both local and remote sensors for easy installation
• Non-intrusive, prompted calibration with programmable cal gas
• Power-up and post-calibration delays eliminate false alarms
• Backlit display for better visibility in low light conditions
• Options for 3x 5A alarm contacts, isolated 4-20mA and MODBUS®
• Security settings to lock critical parameters
• Auto-recognition of Smart Sensors uploads calibration data & more
• Fault supervision circuitry detects failed sensor & transmits warning
• Setup in hazardous area requires only simple magnetic wand
• Optional 9.6 eV sensor suitable for detection of Benzene
• Manufactured in USA

PID (Photo Ionization Detection) technology detects a wide variety of organic and some inorganic gases in ambient air, generally low concentration of complex hydrocarbon molecules; this allows an early warning for presence of these gases in concentrations not seen by conventional LEL detectors.Below is a list of common gases and their ionization potentials, PID technology can be used when the IP value is less than 10.6 eV, the lower the better.

VOCs are organic compounds characterized by a tendency to evaporate easily at room temperature with the potential of forming a toxic gas concentration. While some volatile organic compounds (VOCs) are acutely toxic at low concentrations, the harmful eff ects of most VOCs are delayed. Negative eff ects may occur long after the primary exposure thus many people ignore the potential danger. Long-term eff ects can include leukemia, memory problems, loss of hand-eye coordination, cancer, and a range of other physiological aff ects.

Many personnel throughout the world are unprotected from VOCs in their daily work either because they are unaware of the toxic hazards, or because they are without a monitor that detects for these gas concentrations.

Most VOCs have surprisingly low occupational exposure limits. An increased awareness has resulted in several newly revised VOC exposure limits, including TLVs for diesel vapor, kerosene, and gasoline. Photoionization detectors (PIDs) are able to detect VOCs and large hydrocarbon molecules that are undetectable by catalytic and electrochemical sensors.

Hexane provides a good example. The PEL for hexane in states that follow federal OSHA guidelines is an 8-hour time weighted average limit of 500 ppm. The NIOSH Recommended Exposure Limit (REL) followed by many states is an 8-hour TWA of only 50 ppm. The American Conference of Governmental Industrial Hygienists Threshold Limit Value (TLV) for hexane is also an 8-hour TWA of only 50 ppm. Many federal, state, and corporate health and safety standards require compliance with TLV exposure limits. The lower explosive limit concentration for hexane is 1.1%.

Below 1.1% volume hexane, the concentration of hexane vapor to air is too low to form an ignitable mixture. The most commonly cited hazardous condition thresholds for combustible gas are 5% LEL or 10% LEL. Thus, with a properly calibrated combustible gas reading instrument, assuming the alarm is set at 10% LEL, it would take a concentration of 10% of 1.1%, that is, 0.11% volume hexane, to trigger an alarm. Because 1% volume equals 10,000 ppm, every 1% LEL increment for hexane is equivalent to 110 ppm. It would therefore take a concentration of 1,100 ppm hexane to trigger an alarm set to the standard 10% LEL hazardous condition threshold. Even if instruments are set to alarm at 5% LEL, it still would still require a concentration of 550 ppm to trigger the alarm

The Photoionization Detector (PID) detects a wide variety of organic compounds and some inorganic gases in ambient air. Whether or not a compound can be detected by a PID depends on the lamp energy and the energy required to remove an electron from the target compound molecule (its ionization potential). If the lamp energy is greater than the compounds ionization potential, the PID will detect it.

Due to its sensitivity, a PID is not recommended for high concentrations of target gases. However, a PID does not require oxygen to operate and so would be the detector of choice in conditions where O2 levels are unpredictable. A PID can also react to a number of inorganic substances, including Ammonia, Carbon Disulfide, Carbon Tetrachloride, Chloroform, Ethylamine, Formaldehyde and Hydrogen Sulfide.

A typical PID block diagram is shown below. Molecules of interest (1) are being exposed to high-energy ultra-violet radiation (2), generated by the gas discharge lamp (3). Some percentage of these molecules are ionized, i.e. converted into positively charged ions and negatively charged electrons:

To be ionized, the molecule M should have its Ionization Potential (IP) smaller than the energy of UV lamp photons (E). As a rule, the bigger the difference is between E and IP, the bigger the detector response. Both E and IP are usually measured in electron-volts (eV). For the Ionization Potentials of various chemicals, refer to the Documents tab.

The pair of electrodes (4, 5) is located in the ionization volume near the lamp window. One of them (polarizing electrode, 4) is connected to the High Voltage DC source (7), the other (signal electrode, 5) is attached to the amplifier (6) input. The electric field, created by these two electrodes, forces both electrons and ions to drift towards their respective electrode, by which they are being collected. The resulting small current is being amplified by the amplifier chip and then the output analog signal is recorded and/or displayed in digital or analog format. The output signal is proportional to the concentration of ionizable molecules in detector chamber and thus serves as a measure of concentration. Major air components (N2, O2, CO2) are not ionized by typical lamp radiation and therefore do not generate any detector response. For this reason, PID is very useful for detection of a wide range of VOCs (Volatile Organic Compounds) in ambient air, down to the low-ppb concentrations, without interference from air components.