 Hello everyone. In today's session, we are going to learn about instrumentation amplifier. At the end of this session, students will be able to explain and analyze instrumentation amplifier implemented using operational amplifiers. These are the contents of my presentation. The measurement and control of physical parameters like temperature, pressure, light intensity, humidity are very important in many industrial and consumer electronics applications. A device known as a transducer, a device transducer is used at measuring site to get required information easily and safely. The transducer is a device that converts one form of physical energy into another form. So, generally, a transducer provides equivalent proportional electrical energy signal. The examples of transducers are thermistor, strain gauge, LVDT, LDR, etc. An instrumentation system consists of some type of transducer plus preamplifier as an input stage, instrumentation amplifier as an intermediate stage, and meter or oscilloscope or display system or recorder as an output stage. The major function of instrumentation amplifier is to amplify very low level output signal of a transducer so that its output can drive some indicator or a display system and can be used to control a physical parameter producing it. Of features of instrumentation amplifier for superior performance, the desirable features of instrumentation amplifier are instrumentation amplifier should have high input resistance, it should have accurate closed loop gain, low power consumption, high CMRR, CMRR stands for common mode rejection ratio, it should have high slew rate means the rate of change of output voltage should be high, low noise and low thermal and time drift so output should not change with respect to time or a temperature change in temperature so that is as well as output should contain minimum amount of noise. Now this figure shows instrumentation system in which differential amplifier used as instrumentation amplifier so that is differential instrumentation amplifier with transducer bridge. Electrical bridge is used in which transducer is connected so output of electrical bridge is provided to that is voltage VAB is applied to the two operational amplifiers A1 and A2. Operational amplifiers A1 and A2 are acting as a voltage followers. Output of op-amp A1 and A2 is applied as differential input voltage for basic differential amplifier using op-amp A3 so input for A3 is a differential input and output of this differential amplifier that is working as instrumentation amplifier can be provided to connected to submitter which measures corresponding physical parameter physical quantity. Resistive transducer whose resistance changes as a function of some physical quantity like temperature is connected in one arm of the bridge it is denoted by RT plus minus delta r where RT is resistance of transducer and delta r is a change in RT that is transducer resistance. The bridge is excited powered by either DC or AC power supply for the balanced bridge at some reference condition the voltage VB that is the voltage across resistor RB is equal to voltage across resistor RA VB equal to BA so that can be written as the voltage across RB RB upon RB plus RC into total voltage that is VDC so this is equal to the voltage across resistor RA in electrical bridge RA upon RA plus RF into total voltage that is VDC. After simplification that is it is a ratio of resistor RC to RB is equal to ratio of transducer resistors RT to RA that is RC upon RB equal to RT upon RA. Generally resistors RA RB and RC are selected so that they are equal in value to the transducer resistance RT at some reference condition. The reference condition is the specific value of a physical quantity under measurement at which the bridge is balanced. Normally this value is defined or set by the instrumentation system designer and depends on the transducer characteristics and the type of physical quantity to be measured and desired application. Initially the bridge is balanced at desired reference condition when the physical quantity changes the resistance of transducer also changes. So this causes bridge to unbalance when bridge is unbalanced so voltage across resistor RA that is VA is not equal to voltage across RB that is VB in electrical bridge. So the output voltage of bridge can be expressed as a function of changing resistance of transducer. Let the change in resistance of transducer is delta R since resistor RB and RC are fixed resistors so the voltage across resistor RB that is VB the voltage VB is constant but the voltage VA varies as a function of changing transducer resistance RT. So voltage across resistor RA changes as change in resistance of transducer. So using the voltage divider rule in the bridge let us get the voltage across VA. VA equal to voltage across RA that is RA upon RA plus RT plus delta R change in transducer resistance multiplied by total voltage that is VDC whereas VB is equal to that is voltage across resistor RB is equal to RB upon RB plus RC into total voltage VDC. So voltage VAB that is output voltage of the electrical bridge that is VAB is equal to VA minus VB that is a potential difference. So substituting the value of VA and VB so RA into VDC upon RA plus RT plus delta R minus RB upon RB plus RC into VDC if RA equal to RB equal to RC equal to RT equal to R means all resistors in electrical bridge are of same value then the voltage VAB is simplified to that is output voltage of electrical bridge is equal to delta R upon 2 into bracket 2R plus delta R into VDC. The negative sign minus sign that is indicates that voltage VA is less than voltage VB since increase in value of delta R. The output of bridge VAB is applied to differential instrumentation amplifier using three op-amps. The gain of basic differential amplifier is minus RA upon R1 so therefore output voltage of differential instrumentation amplifier is equal to VAB into gain that is minus RA upon R1. So this is equal to delta R into VDC upon 2 into bracket 2R plus delta R multiplied by gain that is RA upon R1. So generally delta R is very small we can approximate 2R plus delta R approximately equal to 2R. So final output voltage of instrumentation amplifier Vo is equal to RA upon R1 into delta R upon 4R multiplied by VDC. The final equation indicates that output voltage is directly proportional to change in resistance delta R. Since the change in resistance is caused by change in physical quantity or energy meter can be connected at output can be calibrated in terms of units of physical energy. Now student can pause video here and think over this question and try to write the answer. What is the significance of voltage followers A1 and A2 at both inputs of differential amplifier A3 acting as instrumentation amplifier? So op-amp A1 and A2 are acting as a voltage follower they provide very high input resistance and low output resistance. So the op-amp A1 and A2 prevent loading on loading effect of electrical bridge. So maximum voltage is provided to differential amplifier without drawing current from electrical bridge. So to avoid loading effect op-amp A1 and A2 are acting as a voltage follower. This is the reference. Thank you.