Peizoresistive pressure transducers part2

Peizoresistive pressure transducers part2 - SEN2MET Chapter...

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SEN2MET Chapter 6, part 2 SEN2MET Chapter 6, part 2 Week 41 1
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SEN2MET Chapter 6, part 2 Lecture today - Pressure sensor designs with different forms of diaphragms - Static sensor characteristics: Offset voltage, offset temperature variation, sensitivity variation with temperature - Non-linearity, calibration (student reading) 2
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SEN2MET Chapter 6, part 2 Practical pressure sensor designs Critical: Offset voltage and temperature coefficient of offset • If circuit and structure geometries are ideally symmetric, sensor output should be zero for zero pressure input (in a balanced deflection bridge) – Should remain zero for any temperature – Non-zero value at zero pressure = offset • Two factors contributing: 1.non-perfect geometries 2.package stress • We only consider geometric deviations in the deflection bridge 3
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SEN2MET Chapter 6, part 2 Deflection bridge analysis Ideal design: R 1 =R 2 =R 3 =R 4 =R B Layout design variations β 23 14 3 2 1 4 2314 Causing an offset voltage : () ( )( ) 4 4 4 4 where =( ) 4 4 OS OS S S S OS s V RR VV V RRR R V V V β ββ = = +−− ++ = = Equivalent circuit Note that the offset voltage V OS is not temperature dependent if all resistors have the same temp- coefficient But we can have resistor deviations due to process variations 4
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SEN2MET Chapter 6, part 2 Deflection bridge Offset voltage compensation techniques 1. Parallel compensation: is defined by in parallel with (1 ): ) ) 1 For small : BP B PB B RR R R β + ⋅+ = ++ For parallel compensation we can add an external resistor Design example: For 5 , 0.02: 250 Rk R k =Ω= = 5
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SEN2MET Chapter 6, part 2 Deflection bridge Offset voltage compensation techniques 2. Series compensation: SB RR β = Design example: For 5 , 0.02: 100 BS Rk R =Ω= = For series compensation we need to brake the bridge connections 6
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SEN2MET Chapter 6, part 2 Deflection bridge Typical arrangements of deflection resistors to enable compensation 5-terminal version Dual half-bridge version 7
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SEN2MET Chapter 6, part 2 Pressure sensors and temperature compensation
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This note was uploaded on 05/30/2011 for the course SEN 2MET taught by Professor Ulrikhanke during the Spring '11 term at VCU.

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Peizoresistive pressure transducers part2 - SEN2MET Chapter...

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