466 CHAPTER 8. LABORATORY MEASUREMENT AND ANALYSE
5. Capability to interchange instruments and data recorders
is desirable because it allows immediate replacement of
faulty sensors or recorders by using backup instruments or
by relocating sensors. This will help reduce “down time.”
6. The natural frequencies of the sensor’s moving parts must
be high compared to the expected frequencies of the measurements to assure a negligible time lag and an accurate
amplification between sensor and recorder. Also, some instruments will vibrate (“strum”) on their mounts when
placed in the flow. The effects of this strumming on the
measurements must be evaluated.
7. The instrument’s physical size with respect to the scale of
the measurements is very important. Mid-scale and large
scale facilities require more robust equipment (but not as
robust as field instruments), whereas small scale experiments need small, and sometimes delicate, instruments.
In all cases we strive to minimize flow disturbances arising
from the presence of the sensor while providing a commensurate level of resolution.
8. The particular physical geometry of an experiment may
favor one instrument over another.
9. Instruments should be evaluated to determine if they collect data in a form that is suitable for the intended methods
of data analyses.
10. If possible, the instrument should give clear indication of
questionable data values. In other words, failure to obtain
high-quality data should be obvious rather than subtle.
11. Instrument cost and skill required to operate the instrument are always key considerations.
12. Factors related to the instrument’s operation include the
following:
• Instrument sensitivity over the projected range of the
measurements
• Instrument temperature stability or ability to make
temperature compensation
• Ease of calibration and ability to hold calibration over
extended time periods
• Range of environmental conditions in which the instrument can be operated
5. Capability to interchange instruments and data recorders
is desirable because it allows immediate replacement of
faulty sensors or recorders by using backup instruments or
by relocating sensors. This will help reduce “down time.”
6. The natural frequencies of the sensor’s moving parts must
be high compared to the expected frequencies of the measurements to assure a negligible time lag and an accurate
amplification between sensor and recorder. Also, some instruments will vibrate (“strum”) on their mounts when
placed in the flow. The effects of this strumming on the
measurements must be evaluated.
7. The instrument’s physical size with respect to the scale of
the measurements is very important. Mid-scale and large
scale facilities require more robust equipment (but not as
robust as field instruments), whereas small scale experiments need small, and sometimes delicate, instruments.
In all cases we strive to minimize flow disturbances arising
from the presence of the sensor while providing a commensurate level of resolution.
8. The particular physical geometry of an experiment may
favor one instrument over another.
9. Instruments should be evaluated to determine if they collect data in a form that is suitable for the intended methods
of data analyses.
10. If possible, the instrument should give clear indication of
questionable data values. In other words, failure to obtain
high-quality data should be obvious rather than subtle.
11. Instrument cost and skill required to operate the instrument are always key considerations.
12. Factors related to the instrument’s operation include the
following:
• Instrument sensitivity over the projected range of the
measurements
• Instrument temperature stability or ability to make
temperature compensation
• Ease of calibration and ability to hold calibration over
extended time periods
• Range of environmental conditions in which the instrument can be operated