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NT$695

APM / Ardupilot 專用空速計
[MPXV7002DP]

APM / Ardupilot 專用空速計

APM / Ardupilot 專用空速計 

 

Breakout Board MPXV7002DP

(Differential Pressure Sensor board)

 

這個模組是副廠製造的, 品質上與原裝產品一樣, 因都是使用 Freescale 原廠的 MPXV7002DP 壓力傳感器!
  

The MPXV7002 series piezoresistive transducer in the small outline package (SOP) is a state-of-the-art monolithic silicon pressure sensor designed for a wide range of applications, but particularly those employing a microcontroller or microprocessor with A/D inputs. This patented, single element transducer combines advanced micromachining techniques, thin-film metallization, and bipolar processing to provide an accurate, high level analog output signal that is proportional to the applied pressure.

The MPXV7002 is designed to measure positive and negative pressure. In addition, with an offset specifically at 2.5V instead of the conventional 0V, this new series allows to measure pressure up to 7kPa through each port for pressure sensing but also for vacuum sensing (refer to the transfer function in the data sheet for more detailed information).

 

Features:

- -2 to 2 kPa (-0.3 to 0.3 psi).

- 0.5 to 4.5 V Output

Weight: 0.1 oz; 4 g


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使用步驟:

http://code.google.com/p/ardupilot-mega/wiki/Airspeed

Using an Airspeed Sensor

ArduPlane supports the use of an airspeed sensor (shown above), which can help in windy condition, slow flight and autonomous landings. It is not recommended for most new users, however, as it does require additional tuning and adds one more layer of control to set up.

The way it works is that the top tube is "active" (measures air pressure from the pitot tube that is open at the front and has air driven into it by airspeed) and the bottom one is "static" (measures ambient air pressure from tube with intakes on the side).

Here's how to hook it up:

 

On APM 2

Plug it into the pins on the "A0" port, as shown:

Software configuration

You need to enable the airspeed sensor as part of the Mission Planner setup as shown below. You can test that it is working in the CLI by using the "airspeed" command in the "test" menu.

Note: Oscillation between zero and small values (2-3) is normal. The airspeed varies with the square root of the pressure, so for differential pressures near zero it varies quite a bit with very small pressure changes, while at flying speeds it takes much greater pressure changes to produce a similar change in speed. If you see mostly 0, 1, 2, with an occasional bounce to 3 or 4, consider it normal. You will not see that sort of variability at flying speeds. As a check, you can take the fleshy part of your fingertip and press it against the pitot tube to raise the airspeed reading up to say 15 m/s. It is easy to see that holding a significant constant differential pressure like this the reading does not bounce around (if you keep constant pressure).

Installing the Pitot Tubes

When you place the airspeed sensor in your aircraft, use this pitot tube set. The kit comes with a single tube to measure both static and total pressure. In the case of the EasyStar, you'll need to push it through the foam in the cockpit so it points straight into the airstream. Make sure the holes in the side of the tube are not covered. They should be at least 1 centimeter out past the nose. First connect the two tubes coming out the back to the airspeed sensor. The tube coming straight out the back should go into the top port and the tube exiting at an angle should connect to the bottom port on the airspeed sensor. Drill or cut a small hole in the foam and push it through to the front.

If you are using APM in an aircraft with the propeller in the nose, the pitot tube must be mounted out on one wing, at least a foot from the fuselage to be outside the prop flow.

Checking operation

You can check the airspeed reading with Mission Planner or another ground station. Just blow on the pitot tube and observe the response. In still air oscillation between zero and small values (2-3) is normal. The airspeed varies with the square root of the pressure, so for differential pressures near zero it varies quite a bit with very small pressure changes, while at flying speeds it takes much greater pressure changes to produce a similar change in speed. If you see mostly 0, 1, 2, with an occasional bounce to 3 or 4, consider it normal. You will not see that sort of variability at flying speeds.

You can also check it with the ArduPlane CLI in the Mission Planner's terminal screen. Just go into CLI/test menu and type "airspeed". Detailshere.

Finally, you can run a small Arduino sketch that will also test the airspeed sensor. It's here.

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