1. Resistive Transducers Sensors Used in Electronics

2. Key Ideas Resistive transducers are passive devices. They do not generate an electric current. Their resistance changes in response to a change in the environment. They are usually found in a potential divider circuit. When the resistance changes, the voltage balance changes. The processor detects the change.

3. Light Dependent Resistor You can see the CdS track. Its conductivity increases as more light falls on it. Be careful not to confuse the LDR with a photovoltaic cell which does generate electricity when light falls on it.

4. LDR in Circuits Here we see the LDR in a potential divider circuit. In this case Vout will go up as the light level goes up. The next slide shows the LDR in a circuit.

6. Thermistor Thermistors being used to detect high temperature in a power supply …and for a CPU in a computer

7. Thermistor in a Circuit The thermistor has a resistance that changes as the temperature changes. In a negative coefficient component, the resistance goes down as the temperature goes up. In a positive coefficient thermistor, the resistance goes up with temperature.

8. Thermistors The thermistor does not generate electricity with increased temperature. A thermocouple does. Don ’ t confuse the two! Thermistor Thermocouple

9. Potential Divider A simple but very useful circuit. Vout = Vin ×__R2__ R1 + R2 This applies when there is no load. If there is a load, treat it as a series and parallel resistor combination.

10. 05/06/2016 Two simple components: 2) Thermistor – resistance DECREASES when temperature INCREASES 1) Light dependant resistor – resistance DECREASES when light intensity INCREASES Resistance Amount of light Resistance Temperature