A level revision

Sensors

In physics a sensor converts some physical property such as temperature or light to an electrical property such as resistance or voltage. Sensors are usually used in potential divider circuits

Properties of sensors

You need to know 3 key properties of a sensor

Sensitivity

Sensitivity is the amount of electrical change per physical change. For example the change in voltage for the change in light level in a photovoltaic cell. Sensitivity is calculated by dividing the change in the electric property by the change in physical property. For example if a thermistor increases resistance by 10 Ohms when the temperature increases by 5 degrees the sensitivity is:

The units will depend on the what properties the sensor uses. In this case it is Ohms per degree.

Resolution

Resolution is the smallest physical change the sensor can detect, this is usually limited by the accuracy of the measurement devices. For example an ohmmeter, used to measured resistance, may only be able to measure resistance to the nearest 0.01 Ohm. To calculate the resolution of the sensor divide the smallest change in electrical property by the sensitivity of the system:

As both the electrical units cancel out you are left with a value in the form of you physical property, in this case degrees. Our sensor can detect a change of 0.005 degrees.

Response time

Response time is simply the time it takes for the sensor to respond to the change in the physical property it is sensing.