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High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

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Instrumentation amplifiers are intended to be used whenever acquisition of a useful signal is difficult. IA’s must have extremely high input impedances because source impedances may be high and/or unbalanced. bias and offset currents are low and relatively stable so that the source impedance need not be constant. Balanced differential inputs are provided so that the signal source may be referenced to any reasonable level independent of the IA output load reference. Common mode rejection, a measure of input balance, is very high so that noise pickup and ground drops, characteristic of remote sensor applications, are minimized.Care is taken to provide high, well characterized stability of critical parameters under varying conditions, such as changing temperatures and supply voltages. Finally, all components that are critical to the performance of the IA are internal to the device. The precision of an IA is provided at the expense of flexibility. By committing to the one specific task of
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NOZZLE – FLAPPER and DIFFERENTIAL PRESSURE CELLS

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The nozzle – flapper system is widely used in D.P. cells. The form shown below converts differential pressure
(e.g. from a differential pressure flow meter) into a standard pneumatic signal. This is widely used in the control of air operated pipeline valves.
The bellows respond to the differential pressure and moves the lever. This moves the flapper towards or away
from the nozzle. The air supply passes through a restrictor and leaks out of the nozzle. The output pressure hence
depends on how close the flapper is to the end of the nozzle. The range of the instrument is adjusted by moving
the pivot and the zero position is adjusted by moving the relative position of the flapper and nozzle.
This system is used in a variety of forms. Instead of bellows, a bourdon tube might be used and this is operated
by an expansion type temperature sensor to produce a temperature - pneumatic signal converter.