8.1.2 Wind Direction
section provides guidance for procurement of wind vanes; i.e., mechanical
wind direction sensors which rely on the force of the wind to turn a shaft.
Guidance for the procurement of remote sensors for the measurement of wind
direction is provided in Section 9.
wind direction measurement with a wind vane is a relative measurement with
respect to the orientation of the direction sensor. There are three parts to
this measurement which must be considered in quality assurance. These are:
- the relative accuracy of the vane performance in converting position to
- the orientation of the vane both horizontal (with respect to
"true north") and vertical (with respect to a level plane), and
- the dynamic response of the vane and conditioning circuit to changes in
procurement document should ask for:
- the starting torque of the vane
shaft (with the vane removed) which represents a new bearing (and
potentiometer) condition, and
- the starting torque above which the vane
will be out of specification.; when the latter value is exceeded, the
bearings should be replaced.
An example performance specification for a wind
vane is shown in Table 8-2.
range of 1 to 540 degrees was originally conceived to minimize strip chart
"painting" when the direction varied around 360 degrees. It also
minimizes errors (but does not eliminate them) when sigma meters are used.
It may also provide a means of avoiding some of the "dead band"
errors from a single potentiometer. In these days of "smart" data
loggers, it is possible to use a single potentiometer (1 to 360 degrees)
system without excessive errors for either average direction or A.
the wind direction samples are to be used for the calculation of A,
the specification should also include a time constant requirement for the
signal conditioner. Direction samples should be effectively instantaneous.
At 5 m/s, a 1m delay distance represents 0.2 seconds. A signal conditioner
specification of a time constant of <0.2 seconds would insure that the A
value was not attenuated by an averaging circuit provided for another
8. QUALITY ASSURANCE AND QUALITY CONTROL
8.1 Instrument Procurement
8.1.1 Wind Speed
8.1.2 Wind Direction
8.1.3 Temperature and Temperature Difference
8.1.4 Dew Point Temperature
8.2 Installation and Acceptance Testing
8.2.1 Wind Speed
8.2.2 Wind Direction
8.2.3 Temperature and Temperature Difference
8.2.4 Dew Point Temperature
8.3 Routine Calibrations
8.3.1 Sensor Check
8.3.2 Signal Conditioner and Recorder Check
8.3.3 Calibration Data Logs
8.3.4 Calibration Report
8.3.5 Calibration Schedule/Frequency
8.3.6 Data Correction Based on Calibration Results
8.4.1 Audit Schedule and Frequency
8.4.2 Audit Procedure
8.4.3 Corrective Action and Reporting
8.5 Routine and Preventive Maintenance
8.5.1 Standard Operating Procedures
8.5.2 Preventive Maintenance
8.6 Data Validation and Reporting
8.6.1 Preparatory Steps
8.6.2 Levels of Validation
8.6.3 Validation Procedures
8.6.4 Schedule and Reporting