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Written By:Preeti Jain
The $2.5 Billion rover of NASA, Curiosity is all set to take the tiniest detail of the planet Mars. The rover is designed to be highly precise in observing its ambient conditions including atmospheric pressure and the gravitational force. For this purpose, it’s Instrumental Control Unit or the ICU has been equipped with pressure sensors. These sensors will help in detecting the Dust Devils that are a characteristic of the planet and will also detail with the concentration of various gases in the atmosphere at various points. Let’s have a look on what makes a pressure sensor capable enough to perform such specific tasks and where else it can be used.
A pressure sensor is a device which senses pressure and converts it into an analog electric signal whose magnitude depends upon the pressure applied. Since they convert pressure into an electrical signal, they are also termed as pressure transducers.
Need for Pressure Sensors
Since a long time, pressure sensors have been widely used in fields like automobile, manufacturing, aviation, bio medical measurements, air conditioning, hydraulic measurements etc. A few prominent areas where the use of pressure sensors is inevitable are:
1. Touch Screen Devices: The computer devices and smart phones that have touch screen displays come with pressure sensors. Whenever slight pressure is applied on the touch screen through a finger or the stylus, the sensor determines where it has been applied and accordingly generates an electric signal that informs the processor. Usually, these sensors are located at the corners of the screen. So when the pressure is applied, usually two or more such sensors act to give precise location information of the location.
2. Automotive Industry: In automotive industry, pressure sensors form an integral part of the engine and its safety. In the engine, these sensors monitor the oil and coolant pressure and regulate the power that the engine should deliver to achieve suitable speeds whenever accelerator is pressed or the brakes are applied to the car.
For the purpose of safety, pressure sensors constitute an important part of anti-lock braking system (ABS). This system adapts to the road terrain and makes sure that in case of braking at high speeds, the tires don’t lock and the vehicle doesn’t skid. Pressure sensors in the ABS detail the processor with the conditions of the road as well as the speed with which the vehicle is moving.
Air bag systems also use pressure sensors so that the bags get activated to ensure the safety of the passengers whenever high amount of pressure is experienced by the vehicle.
3. Bio Medical Instrumentation: In instruments like digital blood pressure monitors and ventilators, pressure sensors are needed to optimize them according to patient’s health and his requirements.
4. Industrial Uses: Pressure sensors are used to monitor gases and their partial pressures in industrial units so that the large chemical reactions take place in precisely controlled environmental conditions. In oil industry, sensors detail with the depth that the oil rig has reached while exploring.
5. Aviation: In the airplanes, these sensors are needed to maintain a balance between the atmospheric pressure and the control systems of the airplanes. This not only protects the circuitry and various internal components of the airplane but also gives exact data to the system about the external environment. Also, particular levels of air pressure need to be maintained in the cockpit and the passengers lobby to provide nominal ground like breathing conditions.
6. Marine Industry: For ships and submarines, pressure sensors are needed to estimate the depth at which they are operating and for detailing the marine conditions so that the electronic systems can remain safe. Oxygen requirements of under water projects are also regulated by the pressure sensors.
Types of Pressure Measurements
Pressure measurement can either be relative to a reference value or on an absolute scale.
1. Absolute Pressure Measurement: Pressure measured relative to perfect vacuum is termed
as absolute pressure. Perfect vacuum is a condition where there is no matter present in the atmosphere and hence, nil air pressure exists in that region. Absolute pressure sensors have limited usage because it is impossible to attain a state of perfect vacuum. Hence, sensors based on absolute pressure measurement require strict specifications for precise outputs. Sensors based on this type of measurement are used in barometric or altitude related pressure measurements.
2. Differential Pressure Measurement: In differential pressure measurement, pressures of two distinct positions are compared. For example, pressure difference calculated by measuring it at different floors of a tall building will give us differential pressure. Differential pressure measurements, typically taken in pound per square inch differential (psid), are applied when high amount of pressure is to be measured. These types of measurements are used for feed pressure monitoring purposes where the pressure with which the fluid is flowing in a medium is monitored, so that homogeneity in the flow can be maintained.
Differential pressure measurements find an important application in monitoring filters in various types of purification systems. They take the reference of the normal pressure with which the filters clean the fluid. Whenever the filters face the problem of clogging due to contaminants, these pressure sensors give a reading relative to the normal pressure. This helps in keeping the filter clean and operational.
3. Gauge Pressure Measurement: It can be defined as a subtype of differential pressure measurement where we compare pressure at any point to the current atmospheric pressure. Gauge pressure measurement is used in applications like tire pressure or blood pressure measurement. There is no consistency in gauge pressure measurements because atmospheric pressure does vary with altitude and hence its applications are limited to non-critical measurements.