MONITORING STATION INSTRUMENTATION AND MEASUREMENTS - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 56

• Use wire with an ultraviolet (UV)-resistant insulating jacket
• Use insulation and conductor types that are flexible over the full temperature
range expected at the site
• Use shielded and/or twisted-pair cables. Both prevent ambient electrical noise
from affecting measurements. The normal practice is to tie only one end of a
shielded cable's drain wire to earth ground.

Most sensor and data logger manufacturers offer sensor cables that meet these
requirements and are compatible with their equipment.

4.10 MEASUREMENT SYSTEM ACCURACY AND RELIABILITY

Manufacturers use various definitions and methods to express their product's accuracy
and reliability. This section provides the basic information needed to select the proper
equipment and meet the specifications cited in Table 4-1.

4.10.1 Accuracy
The accuracy of any system tends to be dominated by that of its least accurate com-
ponent. For most types of wind resource measurement, that component is usually the
sensor. Errors associated with the electronic subsystem (data logger, signal conditioner,
and associated wiring and connectors) are typically negligible.
The system error of an instrument is defined as the standard deviation of errors
observed for a large number of instruments of that type, with respect to an accepted
standard. For a given instrument, the measured value should be within the quoted
system error of the true value with 68% confidence and within twice the system
error of the true value with 95% confidence. However, the system error applies
only to controlled conditions; factors that may arise in the field, such as turbulence
or tower influences on the free-stream wind speed, are not considered and may be
significant.
Not all manufacturers express system error in a consistent format. The error is
typically expressed in one of three ways:

1 ◦ C)

1. As an absolute difference (e.g., ≤

| Measured value − Accepted standard value |

2. As a percentage difference (e.g., ≤ 3%)

100 Measured value

−

Accepted standard value
Accepted standard value