Pressure sensing elements based ceramic materials becoming more common

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Pressure sensing elements based ceramic materials becoming more common

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Low-cost signal conditioning ceramic pressure sensing elements
Pressure sensing elements based ceramic materials becoming more common feature sensor applications. introduction monolithic device particular even permits sensing elements used applications where cost essence. advantages ceramic sensor elements their minor temperature drifts high media compatibility ceramic material used. major drawback, however, that sensing elements have only small differential output signal (see Table Thus practice high-precision amplifier normally used amplify convert sensor signal. setups such these temperature error sensing element usually just passed through inaccuracies electronics ignored. application outlined here will attempt illustrate system assembled which fulfils industrial requirements without need expensive high-precision amplifier ICs. chips from Analog Microelectronics GmbH used only condition signal also provide sensor system with number other functions.
General description application
application circuitry given Figure uses AM400 signal conditioning sensing element powered with provided integrated voltage reference. AM400 converts amplifies differential output signal pressure sensing element output voltage between referenced ground current loop signal between 20mA 3-wire). entire system operated supply voltage between without need additional voltage regulator protected against reverse polarity short circuits protective functions integrated AM400. following example describes system voltage output between dimensioned. exploiting specific features both sensing element will shown improved temperature drift span achieved without special compensation measures having carried out.
Table specifications ceramic sensing element
Unless otherwise noted, parameters supply room temperature. Parameter Supply voltage Span (Full Scale range) Offset Span temperature coefficient Offset temperature coefficient Bridge resistance Positive pressure Burst pressure Working temperature range Storage temperature range TAMB TSTO Symbol Min. Typ. Max. Unit mV/V mV/V FS/100°C FS/100°C Nominal pressure Nominal pressure
analog microelectronics
Analog Microelectronics GmbH Fahrt 55124 Mainz Internet: http://www.analogmicro.de Phone: (0)6131/91 Fax: (0)6131/91 E-mail: info@analogmicro.de
June 2001 Rev.
Low-cost signal conditioning ceramic pressure sensing elements
VREF VREF Connection 3-wire current-loop
AM400
Voltage Reference
RIAL
IOUT Ground
Figure application diagram using AM400
Equations AM400
general transfer function AM400 output voltage VOUT (circuit Figure VOUT GOUT With regard amplification instrumentation amplifier, amplification output stage GOUT 2.2. Gain external resistors where following applies current output:
with
Sense resistor value approximately independent output current ISET added enable 20mA applications implemented, example. With circuitry given Figure current ISET calculated (VIN VREF
analog microelectronics
June 2001
Low-cost signal conditioning ceramic pressure sensing elements
offset error sensing element amplifier circuit compensated (ZA, zero adjust) order determine offset instrumentation amplifier (connected ground Figure detailed description [3]).
Dimensioning circuit
Temperaturverhalten Spanne Spannungreferenz When dimensioning circuit influence sensing element 19,56 10,30 offset neglected. however 19,54 possible, suggested above, comV 19,52 10,25 pensate offset 19,50 span, value 30mV 19,48 10,20 taken basis calculation. evident Table span drift ver19,46 temperature always negative. 10,15 19,44 Over difference 100°C sens19,42 element span signal decreases 10,10 19,40 about 1%FS markedly lin19,38 curve (see Figure tem10,05 perature range 85°C voltage Temperatur [°C] reference integrated AM400 works opposite direction. Although drift VREF linear value Figure curve voltage reference integrated AM400 span increases about 100ppm/°C. drift ceramic pressure sensing element Figure also gives theoretical curve reference voltage versus temperature. This curve also found other voltage references designed Analog Microelectronics (AM401/11/02/42). such these thus also used follows construct analogue systems:
VREF
Spannungsreferenz
industrial current outputs 0/4.20mA 2-/3-wire applications: AM402 AM442 industrial voltage outputs 0.10V: AM401 AM411 industrial voltage current output parallel with AM400
Figure shows resulting curve span drift after signal been amplified VOUT 0.5V. that percentage span drift over 100°C (e.g. between 80°C) been considerably reduced effect described above without recourse additional external compensation elements. Taking VOUT 0.5V applying this Equation VOUT 30mV value 15.15 then obtained amplification GOP, adjusted. Taking Equation ratio
analog microelectronics
June 2001
Spanne
[mV]
Low-cost signal conditioning ceramic pressure sensing elements
14.15 obtained resistors order minimise remaining voltage caused residual current instrumentation amplifier output (pin load resistor RLIA needs connected [3]. Only then does output voltage VOUT really approaches zero.
Conclusion
setup described above illustrates sensor system with ceramic sensing elements assembled using low-cost integrated circuits. With detailed knowledge sensing elements characteristics which first appear problematic (such temperature drift integrated voltage reference) cleverly exploited reduce temperature drift span Temperature [°C] (TCS) overall sensing element/IC -0,2 system opposed drift sensing element alone. then compensate almost linear temperature drift offset come with inexpensive Figure curve error span system output VOUT when extremely precise solutions better pres- powered VREF sure sensing systems. archive even better results electronically, Analog Microelectronics' concept Frame ASICs then even possible compensate errors electronically. [%FS]
Temperature drift span VOUT 0.5V
Literature
Ceramic pressure cells Internet: http://www.amsys-sensors.com/ Analog Microelectronics GmbH Website: Data sheet AM400: concept Frame ASICs:
analog microelectronics
June 2001
Low-cost signal conditioning ceramic pressure sensing elements
http://www.Frame-ASIC.com/
analog microelectronics
June 2001

Pressure sensing elements based ceramic materials becoming more common

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