Altimeter cloud: Flight device/N-P86-dbe4

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Device information

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General flight settings

This is a snapshot of the settings that were used for this flight. If you want to configure the settings on your own device, pop over to the My devices page and then Configure settings on the device.

Forecast pressure

Set this to your local forecast pressure at sea level. This will offer you slightly improved accuracty for your flight, although it's not 100% essential every little helps!

Xcweather.co.uk is a decent place to grab pressures from for your location and time.

mbar

Launch detect

This is the altitude above the launch pad altitude where the altimeter will trigger itself into recording / flight mode.

The altimeter keeps a constant average of the pressure while waiting for launch, it uses a simple algorithm and the pre-flight buffers to do this. The most recent 120 samples (~4 seconds) are ignored so your pre-trigger altitude won't effect the ground baseline.

For almost all uses we suggest keeping this on the 25 Meter (~82 feet) default settings. If you want to test your altimeter by throwing it in the air, or are planning a very low flight you may want to lower the setting.

meters

Sample ratio

The altimeter runs at 50Hz however you can record every sample or every X samples in order to extend the log time. For example if you set the ratio to 1 it will save 1:1 samples, or if you set it to 3 it will save 1 in 3 samples.

1:

Max samples

This is the maximum samples the altimeter will log per flight. When it reaches this amount it will stop and save the recording.

Recording stop

This setting is how the altimeter decides to stop recording. You can choose either 300 or 600 samples stable or it will record until it's 10000 sample limit unless you press the BUTTON in Manual stop mode.

The samples stable method waits for the devices altitude not to change for the set number of samples. This is defined by not changing by more than +/- 1.0 meters for 98% of the samples, it's a reliable method to stop the recording after landing within 8-10 seconds (300 sample) or 16-20 seconds (600 sample).

Oversampling

Oversampling is a internal setting of the BMP 390 pressure sensor. It is how many samples are taken for each reading. By taking multiple samples for each pressure reading the altimeter reduces noise and increases the resolution of the output.

The sensor can run at 50 samples per second in 4X mode, so we suggest leaving it in this mode as it will offer the highest accuracy.

IIR filter

The IIR filter is another internal sensor for the BMP390 pressure sensor. It is a Infinite impulse response filter used to enhance pressure measurement accuracy by reducing noise. It's primarily for smoothing out rapid pressure changes.

We suggest not setting this too high as it will cause delay to changes in altitude if set very high.

Pressure filter

This filter is a software Kalman filter that runs on the altimeters processor.

The Kalman filter uses a prediction step based on a system model and then a correction step using new measurements to refine its estimate, it creates accurate most certain results from data with noise in it.

Lockout time

The Lockout time is how long the altimeter should stop making decisions and taking actions if it detects unusual high speed altitude changes that are unexpected.
These false readings can be caused by ejection charges (if the altimeter is in the same compartment as the motor ejection gases) or even when you transition to Mach speeds and can give false readings of altitude changes.

When these events are detected the system enters Lockout for the specified time while it stabalises. This effects things like triggering the output, or calculating other data.

Lockout change

This is how we detect a lockout. If the pressure changes by this much in a single sample downwards (pressure increase, lower altitude) then it's likely to be a false reading. Multiply the setting by 32 to get the speed in meters per second that it will trigger at.

Sync sensors

The filters on the pressure sensor can cause it to lag very slightly behind the Accelerometer and Gyroscope data. The Sync sensors option detects how far out of sync these sensors are. It then corrects the Acceleration and Gyroscope readings to match the pressure sensor.

Orientation

This is the orientation you intend to install the Altimeter in your rocket. It's needed to ensure completly accurate angles and orientation charts and reports. Check out the Manual for more information on this.

IMU filter

The IMU filter, or fusion filter takes the data from each axis of the Gyroscope and Accelerometer to calculate the Pitch, Roll, Yaw and tilt angle from vertical. These filters can build up some discrepency over time so it's important to calibrate your sensors to minimise this.

Launch ALP

This is prevention against accidental launch detection.

With this disabled the launch is based only on pressure and something that creates a low pressure can trigger the flight by accident. For example pulling your nose cone off can even trigger it.

With this enabled the rocket also needs to have seen 8 samples (0.25 seconds) of acceleration above this setting in the last 3 seconds as well as the pressure drop to trigger. There is a backup trigger of 1.05 seconds of altitude being above the launch detect setting too.

There are very few situations where this option would cause issues, so we suggest leaving it on.