A sensor can be a technical device or even a organ in the human body that has the ability to detect or sense a signal or physical condition and chemical compounds. In language of physics it is device that can detect the presence or absence of something. For instance a RTD (resistance temperature detector) can detect and measure the temperature. A magnetic device has a sensor that is used to trigger the burglar alarm system when it senses opening of the door. There are other sensors that measure parameters such as light, displacement, heat and so on so forth. Therefore sensors can be displacement sensors, position sensors, laser sensors, temperature sensors etc.
A displacement sensor measures the distance that an object moves. They can calculate the width and height of the object. They are of two types, contact types that use a dial gauge or differential transformer to measure. The other type is non-contact sensors that use magnetic field, laser beam, and ultrasonic wave to make measurements.
A displacement sensor can be in form of a rod, slide or cable operated device.
The type of sensor to be used depends on the length of displacement to be measured. Before making a measurement always ensure if the sensor can be placed near the movement, incorporated in the equipment or should be kept at a distance. Such sensor can be attached to the moving object with a mechanical interface or a spring biased probe. While carrying out the process, always pay attention to the impact of vibration on the sensor. Figure out if such an impact will have a detrimental effect. This will decide whether you should use a contact type or non contact type sensor.
However, there are some factors that affect displacement sensors. Shock is one of them. High level of shock can seriously affect the operation of a sensor. It can damage it forever or degrade the output. The temperature has also to be considered. Some sensors are to be operated within the temperature specifications. Such sensors result in drifting signals due to changes in temperature that is often mistaken as a movement of the object.
Besides temperature and shock, the environmental factors also make their influence on the sensors. In extreme conditions the ingress of harmful particles or liquids can damage the sensor. Incase you will be using the sensor in ambience that will bring it in contact with corrosive materials, then use a corrosion-resistant sensor. In hazardous areas, which are exposed to gases, use a sensor that has been designed and tested for usage under such conditions.
There are two factors that determine the accuracy of a sensor. They are the output signal conformity ('linearity' or 'non-linearity') and the temperature coefficient of the sensor. The resolution of a sensor is the smallest change that it can measure in the output signal. With the advance of technology new sensors have come up that provide almost infinite resolution. The capacity of a sensor to provide repeatable signals is of great significance.
While buying a sensor always consider the supply requirement to the sensor. Most sensors function within the range of 5VDC to 3OVDC. The output from the sensors can differ a little but will be DCV, DCmA, ACV or different digital signals (such as TTL, CAN or R5232). Last but not the least is the ability of a sensor to be able to operate in an electrically noisy environments is crucial.
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