SENSORS

WHAT IS SENSOR…??

A device that detects a physical quantity and converts it into a signal which can be read by an observer or by an instrument.

A sensor is a device, which responds to an input quantity by generating a functionally related output usually in the form of an electrical or optical signal.

 A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes. 

TYPES OF SENSOR

IR sensor Proximity sensor Temperature sensor

IR SENSOR

It is an electronic instrument that is used to sense certain characteristics of its surroundings by either emitting and/or detecting infrared radiation.

In the electromagnetic spectrum, infrared radiation is the region having wavelengths longer than visible light wavelengths, but shorter than microwaves.

WORKING PRINCIPLE

• The IR led keeps transmitting IR infrared rays up to some range infrared range, the IR waves hits the object and comes back at some angle, The Photo diode next to IR led detects that IR infrared rays which got reflected from the object

BASIC CONSTRUCTION

Circuit is divided into two sections. IR TX and IR RX are to be soldered on small general purpose Grid PCB.

ON PCB BOARD

SOUND SENSOR

A device that can detect sound is known as a Sound Sensor

A sound sensor is nothing but a Microphone.

 Based on the power amplifier LM386 and the electret microphone, it can be used to detect the sound strength of the environment. The value of output can be adjusted by a potentiometer.

TEMPERATURE SENSORS

Temperature Sensors measure the amount of heat energy or even coldness that is generated by an object or system, allowing us to “sense” or detect any physical change to that temperature producing either an analogue or digital output.

TYPES OF TEMP. SENSORS

Thermocouple RTD (Resistance-Temperature Detector) Bimetallic Thermostat

BIMETALLIC THERMOSTAT

 Basically consists of two different metals such as nickel, copper, tungsten or aluminium etc, that are bonded together to form a Bi-metallic strip.

Both the metals have different value of linear expansion due to which the metals bend in different proportions

•When Junction is cold – The switch is closed and the current begins to flow

•When junction is hot - The switch is open and the current flow is resisted

RTD (RESISTANCE TEMPERATURE DETEDTORS

RTD’s are precision temperature sensors made from high-purity conducting metals such as platinum, copper or nickel wound into a coil and whose electrical resistance changes as a function of temperature, similar to that of the thermistor.

THERMOCOUPLE

It consists of two junctions of dissimilar metals, such as copper and constantan that are welded together. 

Temp. of ref. junc. = constant

Temp. of measuring junc. = Variable

When the two junctions are at different temperatures, a voltage is developed across the junction which is used to measure the temperature sensor as shown below.

 The voltage difference between the two junctions is called the “Seebeck effect” as a temperature gradient is generated along the conducting wires producing an emf.

Hence O/P voltage is function of temperature

Thank you…