The NORP12 photoconductive cell has a spectral response similar to that of the human eye making it ideal for use in lighting control type applications. The LDR can be any standard type of cadmium-sulphide (cdS) photoconductive cell such as the common NORP12 that has a resistive range of between about 500Ω in sunlight to about 20kΩ or more in the dark. The second leg of the differential amplifier consists of a standard light dependant resistor, also known as a LDR, photoresistive sensor that changes its resistive value (hence its name) with the amount of light on its cell as their resistive value is a function of illumination. That is the difference between the light level for “ON” and the light level for “OFF”. The voltage value at V 1 sets the op-amps trip point with a feed back potentiometer, VR2 used to set the switching hysteresis. A fixed voltage reference is applied to the non-inverting input terminal of the op-amp via the R1 – R2 voltage divider network. Here the circuit above acts as a light-activated switch which turns the output relay either “ON” or “OFF” as the light level detected by the LDR resistor exceeds or falls below some pre-set value. This type of operational amplifier circuit is commonly known as a Differential Amplifier configuration and is shown below: Differential Amplifier Then differential amplifiers amplify the difference between two voltages making this type of operational amplifier circuit a Subtractor unlike a summing amplifier which adds or sums together the input voltages.
![instrumentation op amp offset instrumentation op amp offset](https://www.analog.com/-/media/analog/en/landing-pages/technical-articles/offset-adjust-for-a-differential-op-amp-driving-an-adc/10-blog-1.jpg)
But by connecting one voltage signal onto one input terminal and another voltage signal onto the other input terminal the resultant output voltage will be proportional to the “Difference” between the two input voltage signals of V 1 and V 2.
![instrumentation op amp offset instrumentation op amp offset](https://i.stack.imgur.com/VEAZ0.png)
Thus far we have used only one of the operational amplifiers inputs to connect to the amplifier, using either the “inverting” or the “non-inverting” input terminal to amplify a single input signal with the other input being connected to ground.īut as a standard operational amplifier has two inputs, inverting and no-inverting, we can also connect signals to both of these inputs at the same time producing another common type of operational amplifier circuit called a Differential Amplifier.īasically, as we saw in the first tutorial about operational amplifiers, all op-amps are “Differential Amplifiers” due to their input configuration.