Gas Sensor Experiment

A gas sensor is a device which is used in sensing of various gases without getting influenced by the external environmental conditions. The most important property of a gas sensor should be its selectivity and sensitivity. It should only sense the specific target gas and it should not be sensitive to the changing environmental conditions. In this paper, we see the ideal properties which are important for gas sensing and which makes a sensor ideal for sensing like Selectivity, sensitivity, detection limit, reproductibility , linearity, response and recovery time and sensor response. Carbon nanotube which is a cylindrical structure is used in sensing of these gases. CNTs are very useful for gas sensing because of their high SA and their ability

The multimeter used in the experiment was FLUKE 289.

• TO Header: The TO header provides a mechanical basis for the installation of electronic and optical components such as semiconductors, laser diodes or simple electronic circuits, while at the same time it provides power to the encapsulated components through the pins.

• Mass Flow Controller: A mass flow controller or MFC is a device which is used to control the flow of fluids and gases.

• Multi channel read out systems: The flow of the carrier gas as well as the sample gas is controlled through this system giving us the information of the amount of gas flowing through it.

• PFA tubes: The light weight connectors which connects the cylinder of the gas and mass flow controller.

AIM: To study the detection of MDCP by CNT sample.
a) Using same MDCP concentrations.
b) Using different MDCP concentrations.
EXPERIMENT
a) Using same MDCP concentrations.

The MDCP is kept in the bubbler at a constant temperature. N2 is used as a carrier gas, so as to carry the MDCP vapours it is passed through the bubbler and the saturated MDCP vapour was carried out of the bubbler. The output flow rate of MDCP vapour, FMDCP can be described by the bubbler equation;

FMDCP = (PMDCP/ P0 – PMDCP)Fc ..........................(1) where Fc is the carrier flow rate, Po is the outlet pressure in the bubbler headspace and PMDCP is the vapour pressure of the MDCP which is calculated by Antoine Equation,
PMDCP = 2.844 * 108 * exp(-11500/RT)...............(2)

There are two tunnels where in one of them dilutant is passed and through the other one N2 gas is constantly passed. We connect the Fluke 289 multimeter in order to observe the resistance change of the sensor. The multimeter is connected to the terminal of TO header and N2 is passed continuously for over 600 secs to stabilize the resistance of the sensor. The MDCP gas is then brought into play using N2 as carrier gas and is exposed over the sensor for 30 secs, Keeping the total gas concentration to be 1L/min. After 30 secs the MDCP gas exposure is removed and the N2 gas is passed through the sensor continously for 30 secs which helps it in the recovery. The whole procedure is again repeated after every 60 secs keeping the concentration of MDCP same throughout the experiment. The output of the gas was diluted with