Instrumentation Amplifier – Many industrial systems, consumer systems and process control systems require a precise measurement of the physical quantities like temperature, pressure, humidity, weight etc. A sugar factory requires a measurement of flow, level and temperature of juice. The plastic furnaces require precise measurement of the temperature. The dairy plant requires a precise measurement of temperature and the humidity. Such measurements help the industries to have the production of quality products.
The measurement of the physical quantities is generally carried out with the help of a device called transducer. A transducer is a device which converts one form of energy into another. For example a thermocouple converts the heat energy into an electrical energy, microphone converts the sound energy into an electrical energy, strain gauge converts pressure, force like mechanical energy into an electrical energy. Such a proportional electrical signal output from a transducer can be used further to control or operate the other parts of the system or can be used to get the display or recording of the measured physical quantity,
But most of the transducer outputs are generally of very low level signals. Such a low level signals are not sufficient to drive the next stage of the system. One more difficulty in the practical systems is thatthe transducer used may be mounted on pieces of equipment or structures which are remote from the control location. Long connecting wires or cables are required in such a case, to get the transducer output to the control room. Due to this, the signal which itself is low level, gets subjected to the noise and atmospheric interference. Such a signal may be as low as few mV or even p.V.
Hence before. the next stage, it is necessary to amplify the level of such signal, rejecting the noise and the interference. Hence general single ended amplifier like high gain emitter amplifier is not suitable to amplify such signals. For rejection of noise, such amplifiers must have high common mode rejection ratio. Hence a special amplifier is used to amplify such signals.
The special amplifier which is used for a such low level amplification with high CMRR, high input impedance to avoid loading, low power consumption and some other features is called an Instrumentation Amplifier. Such special featured instrumentation amplifiers have become an integral part of modern testing and measurement instrumentation.
The instrumentation amplifier is also called data amplifier and is basically a difference amplifier. The expression for its voltage gain is generally of the form,