IR Sensors: SAQ Solutions

Listed below are the solutions to the Self-Assessment Questions for IR Sensors.

1. Active sensors detect and emit IR, whereas passive sensors can only detect IR.
   Passive IR sensors have photodetectors or phototransistors to detect IR, while active IR sensors have these components in addition to an IR LED that can itself emit IR to be reflected off of other objects and detected. This is very useful in determining proximity or objects!
2. The potentiometer.
   The variable resistance properties of the potentiometer allows a fine tuning of the IR sensor calibration, which sets the threshold IR level to trigger the desired alarm or detection response.
3. Decreases, increases.
   Because the photodiode consists of the second resistive element of the voltage divider, a decrease in its resistance upon incident light is important because it increases the voltage drop across the first resistor in the voltage divider. This is what triggers the detection signal.
4. False
   Increasing the sensitivity in such a situation will instead lead to background objects or object that the user doesn’t want to detect to be detected. The IR sensor will thus be ineffective in detection.
5. Possible answers: excessive heat, humidity, or sunlight, cracked casing, frequently touching sensor (accumulation of grime), incorrect batteries, misalignment of LED
   Some complications stem from the inability to accurately sense or emit IR radiation (ex: grime accumulation, LED misalignment, and cracked casing). Others come from improper circuit functioning (ex: incorrect batteries, heat, humidity,  and sunlight).
6. Can be used over long ranges
   Because IR radiation detection is dependent on sufficient incident IR waves, it cannot work through impeding objects (IR light can’t get through these objects), and the light will spread out and be too diffuse to extract from background signals.