Piezoresistive Analysis of Pressure Sensor

[emily126]

Hi all~

I am doing a piezoresistive analysis of Pressure Sensor. A square diaphragm (3000?m x 3000?m x 50?m) with 4 resistors above is in interest.The pressure is applied perpendicular to the diaphragm. The resistors are collected in Wheatstone bridge so that the 4 resistors are aligned in the same direction.

I would like to ask, if I apply 5V as the input voltage and the pressure is 1M Pa, what should be the possible output voltage? ( I don't know the resistor value as I model it in ANSYS)

Does anyone have the formula to calculate the output voltage from the input voltage but does not need resistor values?

 

[Comcokid]

There is not enough information in your question to provide an answer.

Piezoresistive pressure sensors (ideally) have four equal-value resistors at zero pressure. The measurement is made from the center resistor pairs of the bridge. At zero pressure (ideally) there is zero volts out. The bridge is designed so one or more of the resistors varies in resistance with pressure, unbalancing the bridge and resulting in a output.

In reality, not all the resistors start out as exactly the same value, nor do all the resistors change the same amount with pressure, and the resistors may also have a temperature coefficient. A sensor manufacturer may use several methods of correction - extra resistors, some of which may have an opposite temperature coefficient, may be applied to the bridge for zero correction, span correction, and to compensate for the temperature coefficient. Alternately, a sensor manufacturer may program the characteristics of the sensor into an EEPROM, which a digitally-controlled gain and compensation circuit may use to correct the output.


For more information, check the following articles:

http://www.sensorsmag.com/articles/1198/fun1198/main.shtml

http://www.analog.com/library/analogDialogue/archives/38-05/AD8555.pdf

 

[AJone]

The resistor value itself will not get you the output. The relative change in resistance is what is needed.

Assuming we are talking about a diffused resistor, the resistor geometery and orientation, crystal orientation, doping concentration/depth, and strain distribution and direction among other items are needed for accurate calculation.

Anyways, it's much more complicated than a metal strain gage calculation. (At least in terms of rough calculations.)

However, we can walk thru some basic calculations if you are still interested. Is this an acedmic exerecise were we can make up some assumptions or do you need real numbers?