Sensors is a tool to detect / measure something, which is used to convert variations in mechanical, magnetic, heat, light and chemicals into the voltage and amperage. In environmental control systems and robotics, sensors provide similarities that resemble eyes, ears, nose, tongue which will then be processed by the controller as his brain (Petruzella, 2001).

Measurement techniques and sensors in an electronic setting function change of physical quantities (eg temperature, force, rotation speed) into a proportional electrical quantity. Measurement techniques and sensors in this arrangement must meet the quality requirements:

1. Linearity
Conversion should really proportional, so the conversion should be linear characteristics.

2. Not dependent temperature
Converter output must not depend on the temperature around him, except the temperature sensor.

3. Sensitivity
Sensitivity of the sensor must be chosen such, that the input values ​​are obtainable output voltage significantly.

4. Response time
Response time is the time required to reach the sensor output value is finally on the input values ​​change abruptly. The sensor must be able to change quickly if the value input to the system where the sensor is changed.

5. Lowest and highest frequency limit
The boundaries are periodic input frequency of the lowest value and highest which still can be converted by the sensor correctly. In most applications require that the lowest frequency is 0Hz.

6. Stability time
For input values ​​(input) the sensor must be able to give a specific output (output) is still value in a long time.

7. Hysteresis
Symptoms of hysteresis on the magnetization of iron can also be found on the sensor. For example, at a certain temperature sensors can give different output.

Four of the nature of the terms of her top, namely linearity, dependence on temperature, time stability and hysteresis determine the sensor accuracy