LDR sensor has a wide range of application. Here is going to mainly talk about the electronic photometry and infrared thermometry.
The photometer can be used to measure the brightness of people and objects, so as to help the photographer choose the appropriate exposure speed. The following is the schematic diagram of the electronic photometer. The LDR photoresistor changes the intensity of light into the difference of resistance value, so that the brightness can be displayed directly by different currents flowing through the meter. Among them, R1 and R2 are used to adjust the surface calibration and W is used to control the sensitivity of the meter head.
The infrared light radiated by the measured object is modulated into 800Hz optical signal by a modulation disc with a filter, which is approximately sinusoidal wave. The modulated light entering into the LDR photoresistor is converted into electrical signals and then sent to the FET amplifier for amplification. The output U0 can reflect the temperature. In order to reduce the influence of noise and temperature change, the working temperature of photoresistor sensor should be about 5℃.
There are many kinds of LDR sensors, and each has its own characteristics. Their spectral response range should be considered when selecting LDR sensors. For visible light applications, cadmium sulfide LDR sensors with good sensitivity and stability are generally selected. Cadmium selenide LDR sensors with high sensitivity and good frequency characteristics can be selected for use under red light. For the light near infrared light, lead sulfide, lead selenide and other LDR sensors should be selected.