Sensor and it's Utility/Function

SENSOR AND IT’S UTILITY/FUNCTION
by. mario batubara
(Installation and Aerospace Observer Unit)
LAPAN – BANDUNG 2008

HISTORY OF SENSOR
Formed in 1967, Sensor established itself as a high quality manufacturer of precision transducers used in the rapidly growing hydrocarbon exploration industry. Aster its formed, sensors had became increasing in many type, function, etc.
DEFINITION
A sensor is a device which measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument
TYPE OF SENSOR
In this era – since sensor was formed, its technokogy has growth as fast as era change. One of them is the type of sensor. Talking about the type of sensor, ofer the world many type of those had made, such as :
1. THERMAL SENSOR
2. ELECTROMAGNETIC SENSOR
3. MECHANICAL SENSOR
4. CHEMICAL SENSOR
5. OPTICAL RADIATION SENSOR

THERMAL SENSOR

TEMPERATURE SENSOR
Temperature sensor is used to measure the degree of heat of thing or anything. Kind of these are (Thermometers, Thermocouples, Thermistors, bi-metal, resistance temperature detectors)

THERMOCOUPLE
The Thermocouple is a thermoelectric temperature sensor which consists of two dissimilar metallic wires, e.g., one chromel and one constantan, coupled at the probe tip (measurement junction) and extended to the reference (known temperature) junction.
The temperature difference between the probe tip and the reference junction is detected by measuring the change in voltage (electromotive force, EMF) at the reference junction.
The absolute temperature reading can then be obtained by combining the information of the known reference temperature and the difference of temperature between probe tip and the reference.

BASIC CONCEPT OF THERMOCOUPLE
Look picture no.1

HEAT SENSOR
The second type of thermal sensor is heat sensor. This is usually to measure heat. Heat, its mean the energy which produced by the its thing’s temperature changing. Type of this sensor are (Bolometer, calorimeter, heat flux sensor)

THERMISTOR
A thermistor is a type of resistor with resistance varying according to its temperature. The word is a combination of thermal and resistor. The relationship between resistance and temperature is linear, then:
ΔR = Kδt
Where :
ΔR = change in resistance
ΔT = change in temperature
k = first-order temperature coefficient of resistance
(if k is possitive, its called PTC and if k is negative its called NTC)

MECHANICAL SENSOR
One of type sensor is mechanical sensor. This is used to measure mechanical quantity such as : altitude, flow, speed, acceleration, pressure, etc.
Here are the pictures of mechanical sensor :

Look picture no.2
HOW IS A GOOD SENSOR?

A good sensor obeys the following rules:
1. the sensor should be sensitive to the measured property
2. the sensor should be insensitive to any other property
3. the sensor should not influence the measured property

Ideal sensors are designed to be linear. The output signal of such a sensor is linearly proportional to the value of the measured property. The sensitivity is then defined as the ratio between output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is a constant with the unit [V/K]; this sensor is linear because the ratio is constant at all points of measurement.