Any electrical engineers ?

No I don't think that will work, it's a Wheatstone bridge, you'd normally connect 5 volts to pin 1, ground pin 3 and measure the output across pins 2 and 4.

The output is normally measured using some form of differential amplifier.

The formula for a Wheatstone bridge is:
0bce336e8aa839df465e82325d169ec810596c1c


Where VG is the voltage across pins 2 and 4, and VS is the supply voltage across pins 1 and 3, R1, R2 and R3 are fixed, RX varies with pressure. Lots of stuff on the web to look at.

I think your be better buying a pressure gauge, that includes the required circuits, unless you want a project and learn about differential amplifiers and Wheatstone bridges.
 
simonfraser said:
ok,

Wide pressure range: 60 mbar to 10 bar | 6 kPa to 1 MPa | 1 psi to 150 psi

only have 0.5 psi pressure :(

can't see a pin diagram for the analog ones, or can i not just wire 5V in and less out ?
Click to expand...

are you referring to the honeywell ones I linked to? Look at the order guide on page 6 and select 5V, analog and the pressure you want, I guess the 60mbar one would do?
I am not particularly recommending that specific one, just pointing out that there are better options than the one you originally linked to.
 
brman said:
are you referring to the honeywell ones I linked to? Look at the order guide on page 6 and select 5V, analog and the pressure you want, I guess the 60mbar one would do?
I am not particularly recommending that specific one, just pointing out that there are better options than the one you originally linked to.
Click to expand...

tnx, the 60mbar would do, how do i wire this up ?

ah, found the data sheet :)
http://www.farnell.com/datasheets/1...0.1822445702.1516611481-1039311889.1516611481
 
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I am also curious as to the application, 0.5 psi full scale is a very low pressure to measure in a tank where water will be sloshing around etc.
 
0.5psi, equivalent to a head of water of about 1 foot.

I won't tell you anything about how much water is in a vented tank, that will always be at atmospheric pressure, irrespective of the water level in the tank.

It will tell you when the fill pipe is full, ie when the tank is full, providing that the fill pipe to the deck fitting is around 1 foot, but the pressure fluctuation caused by the water gurgling in, especially if the fill rate is high for the fill pipe diameter and the vent pipes ability to discharge the displaced air, will probably exceed 0.5 psi, so the circuit would intermittently trigger an alarm. It would work if the fill rate is slow, giving time for the displaced air to escape.

The application note I looked at, I couldn't get the link to work, shows quite complicated circuit, with 4 operational amplifiers driving an analogue to digital converter, and then into a microprocessor, the microprocessor then feeds back a signal to a digital to analogue converter, which intern applies a correction to the summing point on the 3rd opamp.The microprocessor also drives a display.

http://www.farnell.com/datasheets/1...2.1500486352.1516691026-1623992203.1516691026

Quite a complex circuit, I've breadboard thinks like that in the past, not that difficult but it would take some time to work out the various component values and make a stabilised power supply, look after stray noise and generally make good job of it.

I'm not sure whether this is what you had in mind?
 
Ian_Edwards said:
0.5psi, equivalent to a head of water of about 1 foot.

I won't tell you anything about how much water is in a vented tank, that will always be at atmospheric pressure, irrespective of the water level in the tank.

It will tell you when the fill pipe is full, ie when the tank is full, providing that the fill pipe to the deck fitting is around 1 foot, but the pressure fluctuation caused by the water gurgling in, especially if the fill rate is high for the fill pipe diameter and the vent pipes ability to discharge the displaced air, will probably exceed 0.5 psi, so the circuit would intermittently trigger an alarm. It would work if the fill rate is slow, giving time for the displaced air to escape.

The application note I looked at, I couldn't get the link to work, shows quite complicated circuit, with 4 operational amplifiers driving an analogue to digital converter, and then into a microprocessor, the microprocessor then feeds back a signal to a digital to analogue converter, which intern applies a correction to the summing point on the 3rd opamp.The microprocessor also drives a display.

http://www.farnell.com/datasheets/1...2.1500486352.1516691026-1623992203.1516691026

Quite a complex circuit, I've breadboard thinks like that in the past, not that difficult but it would take some time to work out the various component values and make a stabilised power supply, look after stray noise and generally make good job of it.

I'm not sure whether this is what you had in mind?
Click to expand...

I've not read the link but that description sounds like a simple pressure sensor with an external (and micro controlled) amplifier bridge with compensation. All that is included in the sensors I linked to so it can be a simple ADC input on a micro.

But yes, I agree getting a useful measurement could be tricky.
 
Ian_Edwards said:
0.5psi, equivalent to a head of water of about 1 foot.

I won't tell you anything about how much water is in a vented tank, that will always be at atmospheric pressure, irrespective of the water level in the tank.
Click to expand...

Unless you put the sensor at the bottom of the tank where it will tell you the height of water. This could be a reasonable proxy for how full the tank is. This does require a submersible pressure gauge, and possibly a hole in the side of the tank. It would also definitely be susceptible to dynamic pressures from water moving around.
 
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