Gas Sensor and Transmitter Good morning to all of you I am ariz fernandez and im here to present one of the instruments called Gas Sensor and Transmitter Presented by: Ariz B. Fernandez BS Computer Engineering - 5

What are the function of Gas Sensor and Transmitter?

A gas sensor is a device which detects the presence of various gases within an area, usually as part of a safety system. This type of equipment is used to detect a gas leak and interface with a control system so a process can be automatically shut down. A gas sensor can also sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave the area. Gas sensor measures the concentration of gas in its vicinity.

Gas sensors can be used to detect combustible, flammable and toxic gases, and oxygen depletion. This type of device is used widely in industry and can be found in a variety of locations such as on oil rigs, to monitor manufacture processes and emerging technologies such as photovoltaic. Gas detectors are usually battery operated. They transmit warnings via a series of audible and visible signals such as alarms and flashing lights, when dangerous levels of gas vapors are detected.

As detectors measure a gas concentration, the sensor responds to a calibration gas, which serves as the reference point or scale. As a sensor’s detection exceeds a preset alarm level, the alarm or signal will be activated. As units, gas detectors are produced as portable or stationary devices. Originally, detectors were produced to detect a single gas, but modern units may detect several toxic or combustible gases, or even a combination of both types. Gas sensor measures the concentration of gas in its vicinity. Gas sensor interacts with a gas to measure its concentration. Each gas has a unique breakdown voltage i.e. the electric field at which it is ionized. Sensor identifies gases by measuring these voltages. The concentration of the gas can be determined by measuring the current discharge in the device.

Some Applications of Gas Sensor: Process control industries Environmental monitoring Fire detection Alcohol breath tests Detection of harmful gases in mines Home safety

Types of Gas Sensor Metal Oxide Based Gas Sensors Capacitance Based Gas Sensors Acoustic Wave Based Gas Sensors Calorimetric Gas Sensors Optical gas sensors Electrochemical gas sensors

Metal Oxide Based Gas Sensors Metal oxide sensors are also known as chemiresistors. The detection principle of resistive sensors is based on change of the resistance of a thin film upon adsorption of the gas molecules on the surface of a semiconductor. The gas-solid interactions affect the resistance of the film because of the density of electronic species in the film.

Capacitance Based Gas Sensors They measure the change in dielectric constant of films between the electrodes as a function of the gas concentration. The dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space. It is an expression of the extent to which a material concentrates electric flux, and is the electrical equivalent of relative magnetic permeability. Permittivity, also called electric permittivity, is a constant of proportionality that exists between electric displacement and electric field intensity. This constant is equal to approximately 8.85 x 10-12 farad per meter (F/m) in free space (a vacuum). In other materials it can be much different, often substantially greater than the free-space value, which is symbolized eo. The capacitive sensor relies on inter-digitated electrode structures, which correspond to the two plates of a standard capacitor, to monitor changes of the dielectric coefficient of the film. The simple theory behind it is if the dielectric constant of the film is lower than that of the analyte, the capacitance will increase and vice versa.

Acoustic Wave Based Gas Sensors Sound based gas sensors are known as acoustic wave based gas sensors. To launch the acoustic waves, this type of sensor use piezoelectric material either in the thin film form or in bulk form which has one or more transducers on its surface. Then type of acoustic wave generated and device resonant frequency has been determined. Depending on that, it is possible to measure properties, processes, or chemical species in the gas phase, liquid phase, vacuum or thin solid films.

Calorimetric Gas Sensors The principle of calorimetric gas sensors based on change in temperature at catalytic surfaces. It consists of a surface of a film of a catalytically active metal (e.g. Platinum, Palladium or Rhodium) . It burns combustible gases. Heat is generated due to the combustion. This heat is balanced by a reduction in the electrical heating power. Thus the power consumption indicates the concentration of gas.

Optical gas sensors Following methods are used : Ellipsometry (Technique for the investigation of the dielectric properties) Spectroscopy (luminescence, phosphorescence, fluorescence, Raman) Interferometry (white light Interferometry, modal Interferometry in optical waveguide structures) In these sensors a desired quantity is determined by: Refractive index (Speed of the light) Absorbance and Fluorescence properties (of the analyte molecules or a chemo-optical transducing element.)

Electrochemical gas sensors It consists of: Chemical reactants (electrolytes or gels) Two terminals (an anode and a cathode) Anode is responsible for oxidization process and cathode is responsible for reduction process. As a result, current is created. Positive ions flow to the cathode and the negative ions flow to the anode. We can find reducible gases (such as oxygen, nitrogen oxides and chlorine) at the cathode and oxidizable gases (carbon monoxide, nitrogen dioxide, and hydrogen sulfide) at the anode. The output is directly proportional to the concentration or partial pressure of the gaseous species.

Drager PIR 7000

Drager PIR 7000 The Drager PIR 7000 is an explosion proof point infrared gas detector for continuous monitoring of flammable gases and vapours. With its stainless steel SS 316L enclosure and drift-free optics this detector is built for the harshest industial environments, e.g. offshore installations.

Calibration Procedures 1. Zero-point Calibration 2. Sensitivity Calibration Possible Ways of Calibration for the Dräger PIR 7000 — Locally using the magnetic wand (part no. 45 43 428). — Using the Dräger CC-Vision GDS Software. — Using a HART® handheld terminal (only devices with integrated HART® interface). cc-vision Calibrate, configure, and document all maintenance of your Draeger instruments withDrager CC-Vision® Software. A complete maintenance record can be automaticallycreated and stored when calibrating your Draeger monitor with CC-Vision®.  CC-Vision® speeds up your maintenance while drastically reducing the amount of  paperwork. This tool is ideal for ISO 9001 or similar quality documentation. All serial numbers, installed sensors, and configurations are automatically stored with CC-Vision’s® on-board report generation and management system. CC-Vision® also allows the point-and-click setup of your instruments via a “Browser”–type interface, including alarm levels, menus, and sensor status. 

Preparing Calibration ● Provide calibration gas. For gas transmitters with mounted splash guard PIR 7000 / 7200: ● Push calibration adapter PIR 7000 onto the splash guard until it locks into place. For gas transmitters with mounted flowcell PIR 7000 / 7200, bump test adapter PIR 7000 / 7200, process adapter PIR 7000 or process cuvette PIR 7000: ● Connect calibration gas feed directly to the flowcell, the bump test adapter, the process adapter or the process cuvette.

Locally using the magnetic wand (part no. 45 43 428).

Using the Dräger CC-Vision GDS Software The Dräger CC-Vision GDS software is a calibration and configuration software and is available on request. The software allows for the complete calibration of the gas transmitters Dräger PIR 7000 / Dräger PIR 7200. For detailed information refer to the Instructions for Use Dräger CC-Vision GDS (available on installation CD- ROM of Dräger CC-Vision GDS). ● Install Dräger CC-Vision GDS software on your PC. ● Connect the USB PC adapter PIR 7000 and install the driver software, if necessary (enclosed with the Dräger CC-Vision GDS Software). ● Alternatively, use a HART® modem (only for Dräger PIR 7000 / Dräger PIR 7200 with HART® interface, optional).

● Carry out the electrical installation. ● Provide power supply for the gas transmitter to be calibrated. ● Start Dräger CC-Vision GDS software. ● In the start screen of the software, click the icon of the Dräger PIR 7000. ● If communication to the gas transmitter has been established, select Zero-point or Sensitivity in the Calibration menu.

The optional HART® communication allows you to communicate with the gas transmitter via longer distances / cable lengths so that hazardous areas do not have to be declassified. ● While applying zero gas or calibration gas to the gas transmitter, wait for a stable measured value. If the measured value is stable: ● Click the OK button; the corresponding value is accepted by the gas transmitter.

Commissioning ● To avoid false alarms, the alarm activation in the central device has to be disabled. ● Supply the system with power. The gas transmitter runs an internal self-test during which the status indicator's lights flash alternately for a short time. During the first warm-up phase of 60 seconds, the green status light is on and the yellow status light flashes. Operation then subsequently begins using the configuration set on delivery. ● We recommend checking if the factory-preset calibration and configuration match with the intended use of the gas transmitter. Due to national regulations, it may be necessary to run a calibration of the zero-point and the sensitivity (span). ● After installation, Dräger Safety recommends checking the measured value output within the configured measuring range (to the full-scale deflection) as well as checking if all relevant alarms are triggered. ● Enable the alarm activation in the central device to put the system back to normal operating mode. — Wait for warm-up time to end. The Dräger PIR 7000 / Dräger PIR 7200 gas transmitter is either set on delivery in accordance to the details in the table on page 63 and page 64 or is built-to-order. The essential settings of this configuration are specified on the configuration label on the device or on the configuration certificate provided with the device (see page 8). The device has been factory-calibrated, so after finishing the electrical and mechanical installation, the device is ready to operate. The gas transmitter distinguishes between two warm-up phases: Warm-up phase 1: Duration: 60 seconds. Green status light on, yellow status light flashes. The gas transmitter is in maintenance mode and provides the configured maintenance signal. No digital measured value is output via the serial interface or the HART® interface. Warm-up phase 2: Duration: 180 minutes. Green status light on. Gas transmitter is ready for use. A corresponding digital warning is output via the serial and the HART® interface. When warm-up phase 2 is finished, the warm-up phase of the gas transmitter is typically completed. The gas transmitter then reaches the specifications stated in the “Performance Characteristics (typical values)”

LITERATURE CITED: http://scholar.google.com/scholar?hl=en&lr=&q=ga s+sensor http://en.wikipedia.org/wiki/Gas_sensor http://en.wikipedia.org/wiki/Hydrogen_microsensor http://vernier.com/probes/co2-bta.html http://sensors- transducers.globalspec.com/LearnMore/Sensors_ Transducers_Detectors/Gas_Sensing/Gas_Sensor s http://etd.ncsi.iisc.ernet.in/handle/2005/281 Proceeding of the 2000 Hydrogen Program Review, NREL/CP-570-28890 http://www.gasdetection.com/TECH/sensorprincipl e2.htm http://physicsworld.com/cws/article/news/17869

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