Analog front ends for network appliance and gas sensors

Liquefied petroleum gas (LPG) is the most commonly used gas found in our homes. Leakage of LPG can be life threatening. Even in low concentrations it can be suffocating whereas if the concentration is high enough it can lead to a fire or cause a blast. Hence, it is extremely important to monitor the LPG level in our surroundings. Another type of gas that needs to be constantly monitored and kept within certain limits is CO2. High embedded system concentration levels can cause breathing problems and prolonged exposure can lead to death.

We can prevent gas exposure-based COMe Module accidents from happening by recording and maintaining gas levels in the immediate environment. Gas sensors can play a key role to this effect by raising an alarm when the level crosses prescribed safe limits. Advances in modern semiconductor technology have empowered us to design low-cost and low-power sensing solutions to make embedded system our homes, offices, and network appliance lives safer by keeping a check on the gas levels in our surroundings.

Every sensing system comprises a basic network appliance element that measures one or more electrical parameters like resistance or capacitance, and a circuitry that measures the changes in those parameters. Most of these sensors can operate on battery power so they can work uninterrupted for years on end. Hence, it becomes imperative that they consume low power for their operation. To pass the sensed information to the controller, analog front ends (AFE) are used. These allow the microcontroller to understand analog signals sent by sensors by converting them to a digital signal and then performing post processing on the received data.

Parameters measured by sensors: sensors measure changes in resistance and capacitance.

Resistance
There are two common ways to measure a change in resistance: a potential divider COMe Module circuit and passing a known current. First, in a potential divider circuit, we connect a sensor whose resistance varies depending on some physical parameter like temperature, network appliance, etc. We compare the changing value of the sensor to a fixed value resistance. In such a circuit, the voltage of the connecting node (ADC) of the fixed resistance and the sensor depends on the resistance of the sensor and thereby on the physical parameter being measured.

refer to:
http://embedded-computing.com/articles/analog-front-ends-for-gas-sensors/