what is a strain gauge pressure sensor?

Answer 1

Snow gave a good description of one type of strain gauge pressure sensor. Larry missed up the piezoresistive property of strain gauge with the piezoelectric property of quartz. Piezoresitive is the ability of the material to change its resistivity (not to generate charge) with applied stress.

Typically to make a pressure sensor, a Wheatstone bridge of two pairs of strain gauge resistances are placed behind a metal diaphragm: two in the center to sense the tension, two near the edge to sense compression.

In addition to metal, there are Silicon-diaphragm pressure sensors. Several p-type doped silicon make good piezoresistive material. Many of which with one very very wonderful property: When compressed in the 110 crystal direction, the resistivity changes at an increasing rate with stress. The Si pressure transducers industry exploits this to make sensors with high amplitude linearity. Si-diaphragm can also be made very small to have high natural frequency (up to 300KHz) this allows the measurements of dynamic pressures, e.g. in optimizing scaled-down aircraft models in wind tunnels, or in studying explosive expansion characteristics.

Si-diaphragm, however, suffers breakdown at relatively low temperature so its sensors can only be used at up to about 120C. A metal diaphragm pressure sensor is typically too big to have a good natural frequency. Hence the industry has a type of piezoresistive pressure sensor called SOS (silicon on sapphire). This sensor can have both small size and high temperature properties, and hence can be used in dynamic pressure studies such as the pressure curve on the exhaust manifold of an internal combustion engine.

Answer 2

Its a strain gauge attached to a plane which predictably undergoes a strain (according to a certain relationship, within required tolerances) under an applied pressure. IT DOES NOT DIRECTLY READ PRESSURE!! For example, if you attach a strain gauge to a coke can (and set your output voltage to read zero), and open the coke can, there should be a negative strain due to the can shrinking.
This value will be dependant on the direction in which the strain gauge is placed.
To calculate the pressure, you need to choose a strain/pressure relation, and align the strain gauge to the axis you are investigating.
"Strain gauge pressure sensors" must be tailor made for every application, ie. you can't just stick one on something and get a pressure reading. You need to
(a) Know a relationship between a strain in your vessel and the pressure you want to measure. (may be difficult if strange geometries are involved)
(b) Attach the strain gauge along the correct axis.
(c)Calibrate the strain gauge to give you a zero reading at a reference strain/pressure. (If the pressure you are measuring can't be changed temporarily to a known value like atmospheric pressure, you will need a duplicate pressure vessel)
(d) Read the strain gauge at the pressure you want to measure
(e) Use the relationship in (a) to figure out what pressure your measured strain corresponds to.
(f) Know exactly how accurate your measurement and calculations are.

Answer 3

I made one of these a few weeks ago...

Basically, take a peice of pipe, and weld a thin circular disk to one end of it. Then apply a strain guage, which is a device for measuring the deflection of metal. You can measure the deflection at zero pressure, and at your high pressure. Then use those values to determine a scale factor which directly relates the pressure. The strain in the plate is linear with pressure.

You can also purchase factory made strain guage pressure sensors, otherwise known as transducers. They work the same way, and contain electronics to output the calibrated strain into a 4-20 mA signal that can be used to directly read pressure, or a voltage output which is also correlated with a given pressure range.

Is that what you were looking for?

Answer 4

It is an instrument that relies on the piezoelectric effect to correspond to a value of pressure or strain in a given apparatus.
Piezoelectric effect is where a substance, for example, quartz, yields a slight amount of electricity when pressure is applied to it. The value of the electricity is proportional to the strain placed on the crystal.
So assume you have a crystal mounted on the surface of a pressure vessel. Then the pressure in the vessel can be determined by the voltage being generated by the crystal.