Presence Sensors.

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic or electrostatic field, or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor might be suitable for a plastic target while an inductive proximity sensor requires a metal target.

Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object. A proximity sensor is divided in two halves and if the two halves move away from each other, then a signal is activated. An example application of a proximity sensor is for window security. When the window opens an alarm is activated.

Environmental sensors include those used to measure temperature, humidity, wind speed, barometric pressure, etc. They are often connected in a network. An analog humidity sensor gauges the humidity of the air relatively using a capacitor-based system. The sensor is made out of a film usually made of either glass or ceramics. The insulator material which absorbs the water is made out of a polymer which takes in and releases water based on the relative humidity of the given area. This changes the level of charge in the capacitor of the electrical circuit.

Exercise 8. Match given types of Sensors with definitions

Velocity sensors, Motion sensors, Vibration sensors, Environmental sensors, A proximity sensor, A thermistor, Thermocouple, Pressure sensors, Force sensors, A strain gauge.

-a passive resistive device that changes its physical resistance with temperature producing a measurable voltage depending on the current through the device.

-converts thermal energy into electrical energy.

-used to obtain an accurate determination of pulling and/or pressing forces.

-a device used to measure the strain of an object. A positional sensor is one that permits a linear or angular position measurement.

-used to measure pressures of gases or liquids.

-include those used to measure temperature, humidity, wind speed, barometric pressure

- a sensor able to detect the presence of nearby objects without any physical contact.

-are sensors for measuring, displaying and analyzing linear velocity, displacement and proximity, or acceleration.

- measure the linear velocity of an object using either contact or non-contact techniques.

-designed to measure the rate of change of position, location, or displacement of an object that is occurring. Displacement sensors measure the distance an object moves and they can also be used to measure object height and width.

Lesson six