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X-320M™ User's Manual Appendix F: Methods and Calculation Details
Appendix F: Methods and Calculation Details
The following section describes the methods and calculations used for X-320M™ instrument
measurements and derived values.
Sensor Acquisition Periods
Sensors connected to X-320M™ are sampled or updated every 2 seconds.
Analog values are captured every two seconds.
1-Wire sensors are read every two seconds.
Frequency and counter-inputs counts are accumulated during the two second period, and the
measurements are derived from the accumulated value.
Solar measurements are only captured once per minute.
Actions associated with input state-changes are acted on when detected; they are not synchronous with
the two second acquisition period.
Calculated values (Wind Chill, Dew Point, and Heat Index) are updated every 2 seconds.
Note: The measured and calculated values are not retained by X-320M™ during a power loss.
Compensation
Once the raw measurement is taken, the Slope and Offset are applied.
y
=
mx
+
b
y = Adjusted Value
m = Slope
x = Raw Value
b = Offset
After the Slope and Offset are applied, further calculations are applied that are dependent on the sensor.
These calculations are described below for each sensor. Some values, such as heat index, are
calculated based on measurements from a combination of sensors.
Measured Values
Wind Speed
The Wind Speed reading, by default, is a running average of 30 samples per minute over the Avg.
Period specified in the
Wind Spd . setup tab. The default Avg. Period is 2 minutes, which would use 60
samples to calculate the displayed wind speed. The maximum Average Period is 10 minutes. As new
readings are made, the oldest values are replaced.
If the Averaging Period is set to 0, then the instantaneous wind speed is given, which is calculated from
the instrument counts over a 2 second period.
Note: Wind Speed and Wind Direction use the same Averaging Period. Changing the Avg. Period in
either setup page will affect the other setup page.
Wind Direction
The Wind Direction is a running average of 30 samples per minute over the Avg. Period specified in the
Wind Dir. tab. The default Avg. Period is 2 minutes. The maximum Average Period is 10 minutes. As
new readings are made, the oldest values are replaced. If the averaging period is set to 0, then the
instantaneous Wind Direction is given.
Note: Wind Speed and Wind Direction use the same Averaging Period. For example, if the Averaging
Period is changed from 2 minutes to 4 minutes, both Wind Speed and Direction will be changed to 4
minutes.
Internally, the polar coordinates are converted to Cartesian coordinates and then stored. The running
average is calculated using the Cartesian coordinates. These running averages are then converted back
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