Direct sensing

Applications of Physics Direct Sensing – Part 1 Mukesh N. Tekwani [email_address] CIE – A2 Level, Nov 2009

Direct Sensing ,[object Object],[object Object],[object Object],[object Object]

Examples of Sensors ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Electronic Sensor ,[object Object],Sensing Device – Example: LDR (L ight D ependent R esistor ) – to measure changes in light Strain gauge – to measure strain experienced by a material Important – Some physical property of the sensing device MUST change so that it can detect changes in whatever is to be monitored. Sensing Device Processing Unit Output Device

Electronic Sensor ,[object Object],Processing Unit Any change in a physical property of the sensor must be processed. (measured / converted / amplified) so that it can be indicated by an output device. Output Device The output device may be a simple lamp or a digital meter that indicates a voltage or a current – basically any device that can respond to a change in voltage. So: Connect the sensing device to the output device via a processing unit Sensing Device Processing Unit Output Device

Light Dependent Resistor (LDR) ,[object Object],[object Object]

Light Dependent Resistor (LDR) ,[object Object],[object Object],[object Object],[object Object]

Characteristics of LDR ,[object Object],[object Object],[object Object],[object Object],[object Object]

LDR Characteristics ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

LDR Characteristics ,[object Object],[object Object],[object Object]

LDR ,[object Object],[object Object],[object Object],[object Object],[object Object],An LDR has a resistance of 15 ohms at a certain very high light level. What value of protection resistor is needed if a current of no more than 10 mA is to flow when the supply voltage is 9.0 V?

Potential Divider Circuit An output voltage Vout is obtained from a junction between the two resistors.

Potential Divider circuit ,[object Object],[object Object]

[object Object],So, Vout = So, the output voltage is the same fraction of the input voltage as R 2 is the fraction of the total resistance .

LDR Problem What is the output voltage of this potential divider?

LDR ,[object Object],[object Object]

Direct sensing

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Direct sensing