Pressure differential LED project.

[Boncuk]

Pressure differential LED project

Hi tsneidin,

you've got a point here. Better make a new thread about pilots, those of them who never were pilots and model aircraft pilots.

Here is a suggestion: If your reference pressure has a constant value you won't need a pressure sensor there. The transducers you have selected have an output range of 1 to 6V. That has to be reduced to 0 to 5V in order to control the LM3914 circuit properly. Use a difference amplifier to achieve that.

Use another difference amplifier to compare the measured pressure value with the reference pressure which should equal 5V. The higher the voltage difference the more LEDs will be lit. Check the schematic. It contains the difference amplifier and the appropriate LM3914 circuit to illuminate 10 LEDs at full difference and none at zero difference.

You can use a TLC271 instead of an LM324. That's one the simulation works with. Notice the voltage difference. There is an input voltage of 4.49V resulting in an output voltage of 0.51V. 0.5V is the minimum voltage to have the first LED illuminated (5V/10LEDs=0.5V per LED)

Regards

Boncuk

Edit: Don't forget current limiting resistors for the LEDs. Omitted for simulation purposes. The monitor doesn't fry because of that. RV=VDD-Vf/If (R(Ohm)=VDD(V)-Vf(V)/If(A))

 

[audioguru]

I think a differential sensor is used because the air pressure changes with altitude.

 

[Boncuk]

I think a differential sensor is used because the air pressure changes with altitude.

Hi audioguru,

in aviation pressure sensors with one pressure port are used. The other one is sealed with standard atmospheric conditions on one side of the diaphragm. The result is pressure altitude based on the standard atmosphere if the altimeter is set to standard 1013.2mb or 29.92in. For take-offs and landings the local pressure value is set resulting in indicating height above field elevation.

Differential pressure sensors have two pressure ports, one for low pressure (vacuum, more or less) and the other for high pressure. Measuring the total pressure of a fan the low value port must be connected inside the suction plenum and the high value part to the pressure chamber of the fan. They are also used to measure airspeed. The static pressure goes to the low port and the dynamic pressure to the high port. The difference of both is used to calculate the airspeed. (a pitot tube e.g. has two pressure output ports)

Pressure differential measurement is also used to move the ramps of the air intake duct for supersonic flight. (Supersonic air is not supposed to enter the engine - result=flameout)

In the particular case concerning the threat one side of the sensor goes to the reference pressure causing the diaphragm to deflect negative. Connecting a pressure source to the other side the diaphragm will return to neutral position if pressures are equal and the readout is zero.

Regards

Hans

 

[Leftyretro]

Pressure sensors come in 3 basic configurations:

1. Absolute pressure. This is a pressure sensor where the low pressure port has been evacuated to as near a perfect vacuum as possible and sealed. The active port will respond to positive pressure changes and can be calibrated in various engineering units (inches of mercury for barometer use) and would typically display 14.7 PSIA at sea level if scaled for PSIA readout. This is the type of pressure sensor used to measure elevation and elevation also requires the ablility to mechanically or electronically trim the calibration to compensate for local changes in barometric pressure due to weather conditions. The high top range is dependent on the specific sensor design.

2. Gauge pressure. This is a pressure sensor where the low pressure port is left vented internally and unavailable to the user. The active port will respond to pressure changes but because the low port is vented this will always measure 0 PSIG if the active port is vented to atmosphere no matter what changes there are to local barometric pressure or how high in elevation the sensor is moved to. The top of range depends on the specific sensor specs.

3. Differential pressure. This is a two port pressure sensor that only measures the difference between the high and low user ports and is not affected by local barometric or elevation changes, just the difference between the two ports. Some can read both negitive and positive differential pressure by and have a "center zero", others only read in one direction but the port tubing can always be swapped to cause a positive reading. The top of range depends on the specific sensor specs. This is the type of sensor used to measure flows, speed, liquid levels, pressure drop across some item, etc.

People tend to not add the A or G when using the PSI units and sometimes that can be misleading or misunderstood as it assumes the reader knows what kind of pressure reading is being performed and the type of sensor being used.

In summary all pressure sensors are two port sensors, it just depends if the second port is avalible to the user and if not, if it's evacuated and sealed or just vented internal to the sensor.

Lefty

 

[Aeroplane]

Any progress? how about this

Pressure Differential Sensor Motorola MPX2010DP

The ZD-1904 piezo resistive pressure sensor provides a very accurate and linear voltage output directly proportional to the applied pressure. The sensor housed a single monolithic silicon die with a strain gauge and thin film resistor network on each chip.
Specifications:
* 0°C to 85°C temperature compensation
* 0 to 10kPa (0 to 1.45 psi)
* 25mV full scale span



MPX2010DP.pdf QTY
1+ $39.95
10+ $35.90
25+ $27.90
https://www.electro-tech-online.com/custompdfs/2008/12/MPX2010DP.pdf

**broken link removed**