Pressure measurement of a piezo resisitve sensor

[Willykilly]

Hi all,
I was told by my friend that I need a 4mA current source for measuring a output from a pressure sensor. Why is that required?

Thanks in advance.

 

[keith1200rs]

pressure measurement

What is the pressure sensor? Without some more details it is impossible to answer.

Keith

 

[Willykilly]

Re: pressure measurement

Hi all,
Thanks for the reply. I am using a piezo resisitve sensor and a strain guage.

 

[keith1200rs]

pressure measurement

What is the pressure sensor, what strain gauge? Without some more details it is impossible to answer!!!

Keith

 

[weeyndha]

Re: pressure measurement

hello willykilly

if you use piezoresistive then you must supply the sensor using a stable 4 mA current source then amplified using charge amplifier. Some piezoresistive sensor already have current source and charge amplifier in it.

Regards

 

[FvM]

Re: pressure measurement

You're confusing piezoresistive with piezoelectric sensors. Piezoresistive sensors don't use charge amplifiers, just instrumentation
amps (differential amplifiers). Their operation principle is resistance change rather than charge generation, you can imagine them simply
as silicon manufactured strain gauges. As with a conventional (metal wire or foil) strain gauge, the bridge circuit turns a resistance
difference in a voltage difference.

Various supply options for piezoresistive bridges are in use. A few manufacturers actually prefer constant current supply, more use
constant voltage or special designed temperature compensating networks. As keit1200rs mentioned:

Without some more details it is impossible to answer!

 

[pakitos]

pressure measurement

HI there can you give info concerning the DMP015-A?
I found out that Vsignal = Vexc*(delta R)/R
= Vexc*F*S
s=sensitivity in mV/v
F= force
but in this datasheet no mv/v value was found
thx

 

[keith1200rs]

pressure measurement

140mV for 5V excitation,full scale, according to the data sheet.

Keith.

 

[pakitos]

pressure measurement

thx

there are two positive and two negative excitations why?

 

[keith1200rs]

pressure measurement

Just duplicate connections.

Keith.

 

[pakitos]

pressure measurement

I tried to give 5v and gnd to one then to both: the output changed. So this means that they are not connected together. Isn't it? Strange

 

[keith1200rs]

pressure measurement

It sounds like the two halves of the bridge are not connected internally, or through a high resistance.

Keith

 

[pakitos]

pressure measurement

in both cases when I tried to put pressure nothing happened at the output. Do I needed to use a differential amplifier to feel the change?
thanks for your help

 

[keith1200rs]

pressure measurement

You need to measure the voltage between the +out and -out. Bear in mind you only get 140mV from 15psi, but you should be able to see it on a multimeter.

Keith

 

[pakitos]

pressure measurement

well i got nothing when i pressed

 

[keith1200rs]

pressure measurement

What are you 'pressing'? It is an air pressure sensor.

Keith

 

[pakitos]

pressure measurement

how to try it then?
by force they mean air pressure?

I know air pressure sensors have a small tube where you can blow. This one is flat from both ends.

 

[keith1200rs]

pressure measurement

It is meant for sensing atmospheric pressure so it doesn't have a tube connection (although there is a version which does). I would suggest you try to find a tube that is something like 10mm diameter. You could then hold the end over the sensor & blow. Or cut a bicycle inner tube up and put it inside.

Keith.

 

[pakitos]

pressure measurement

ah ok, thanks sir, I thought by pressure any pressure. So it will measure the amount of air on the sensor surface Right? I asked for weight sensor they gave me this. This is why I thought it will sense any pressure.
Thanks again

 

[keith1200rs]

pressure measurement

Sorry, it is definitely an air pressure sensor.

Keith.