Environmental Engineering Reference
In-Depth Information
3. As a minimum ratio to the accepted standard value (e.g., 95% accuracy)
100
Minimum Measured value
Accepted standard value
Accuracy is often confused with precision. System precision (sometimes also
expressed in terms of standard deviation) refers to the consistency of repeated values
recorded by the same instrument under the same conditions. Precision may also refer
to the number of digits reported by the data logger. To avoid rounding errors in
subsequent analysis, it is recommended that values be recorded to one significant
digit greater than the nominal precision.
4.10.2 Reliability
System reliability is the measure of a system's ability to constantly provide valid
data. Vendors usually test the reliability of their equipment to determine the product's
life cycle. They will often cite a mean time between failures under certain conditions.
Although this information is helpful, one of the best indications of a product's reliabil-
ity is the experience of other users. The vendor can be asked for references, and users
can be contacted at conferences and workshops. The user also has an important role to
play in ensuring system reliability by strictly following the manufacturer's guidelines
for installation and operation, using redundant sensors to maximize the recovery of
critical data, and implementing a comprehensive quality assurance plan.
4.11 QUESTIONS FOR DISCUSSION
1. What are the basic environmental parameters measured in all wind resource
assessment campaigns? What type of devices are used to make the measure-
ments?
2. Using the Internet, identify an anemometer that has sufficient technical informa-
tion available to determine if it would be suitable for a wind resource assessment
campaign. What is the accuracy of the device, and how is it expressed? What
is the distance constant for the device? Would you use the device for a wind
resource assessment campaign? Why or why not?
3. Using the Internet, identify a complete tower and instrumentation package for
wind resource assessment, including pricing and delivery information.
4. Suppose you are measuring the wind resource at a high elevation site in very
steep terrain where winters are very cold and severe. Design an instrumentation
package that you think would provide the information needed for an accurate
resource assessment.
5. What might be the purpose of having two anemometers at the same height on a
mast? Why not do the same with other sensors, such as direction, temperature,
or pressure sensors?
Search WWH ::
Custom Search