Potter T.D., Colman B.R. (co-chief editors). The handbook of weather, climate, and water: dynamics, climate physical meteorology, weather systems, and measurements
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3 PLASTIC FABRIC ATION
Two identical units of a second prototype design were delivered in March, 1981 (Fig.
2). The main purpose of these prototypes was to develop a streamlined and econom-
ical fabrication method since cost reduction was one of the primary design goals.
The main housing, nose cone, and tail assembly of these units were constructed of
thermoformed black vinyl plastic. Wood molds were fabricated for forming the main
housing and tail in two identical halves, which were then cemented together. These
molds could be easily modified to incor porate any desired changes. The tail assem-
bly was filled with polyurethane foam. To achieve the desired combination of rigid-
ity and low weight several different thickness and color vinyl materials were tried as
well as different foam densities. The wind speed and wind direc tion transducers were
the same as those used in the first prototype. A total of six sensors of this design
were fabricated for evaluation by a couple of different organizations.
Work on a third prototype design was already underway while prototype II units
were being field tested. We acquired a small injection molding machine ( previous
injection-molded propellers were made by an outside supplier) and began to redesign
the nose cone assembly and other internal parts for injection-molding. To minimize
outdoor ultraviolet (UV) deterioration, we had selected a black vinyl material for
Figure 2 Second prototype wind sensor, March, 1981.
766
COMMERCIAL RESPONSE TO MEASUREMENT NEEDS
thermoforming the main housing and tail assembly. The wind speed and wind direc-
tion transducers remained the same. A machined aluminum mounting post with set
screws provided for mounting on standard 1-in. schedule 40 pipe. This design was
designated as Model 05101 Wind Monitor. Approximately 25 units of this design were
produced in January, 1982. Field testing of these and the previous prototype units
revealed a problem with the black vinyl softening in the hot sun and residual expansion
of the internal foam causing irregular bumps in the surface of the tail assembly.
We changed to a superior material for thermoforming the main housing and tail
assembly. The new material was a white ABS (Ac rylonitrile-Butadiene-Styrene)
plastic with UV inhibitors, which had been developed and extensively tested speci-
fically for long-term outdoor exposure. Some changes were made in the shape of the
main housing, and additional mating par ts were designed for injection molding. An
aluminum orientation ring was also supplied. The orientation ring, which was
installed directly below the mounting post, had an index pin that allowed the
sensor to be removed and replaced for service while maintaining its original orien ta-
tion on the pipe support. These changes, which were included in the next production
lot of 60 units produced in April, 1982 (still designated Model 05101), made a
dramatic improvement in the performance of the sensor, especially in tropical condi-
tions (Fig. 3).
Figure 3 Model 05101 Wind Monitor, April, 1982.
3 PLASTIC FABRICAT ION 767
4 CUSTOMER INPUT
Meanwhile a number of changes in design continued to be made in response to
customer requests. The most significant change was the wind speed transducer. The
Hall switch was replaced with a coil that was wound on a bobbin with a central hole,
which allowed space for the potentiometer coupling to pass through. The wind speed
signal then became an alternating current (ac) sine wave (in place of the 5-V square
wave from the Hall switch) with the frequency directly proportional to wind speed.
The main advantages of the coil were greater reliability and the elimination of the
magnetic attraction of the soft iron flux plates required for the Hall switch that
caused a noticeable ‘‘jogging’’ of the propeller at threshold wind speeds. A separate
sensor interface circuit was developed to convert the wind speed signal to a square-
wave pulse output (similar to the Hall switch) as well as a calibrated analog voltage
output (0 to 1 V ¼ 0 to 100 mph). A smal l metal junction box with a terminal strip
was added to the sensor mounting post to provide an easy cable connection point.
Designated Model 05102 Wind Monitor, approximately 340 units of this design
were produced between October, 1982, and July, 1984.
Early in the fall of 1983 we had begun to incorporate additional changes desired by
NDBC and other customers. The potentiometer was changed from 1 kO, 352
function
angle to 10 kO with a 355
function angle. NDBC also wanted a reduction in the
number of external fasteners, which were difficult to deal with in a marine environ-
ment. Meanwhile Climatronics Corporation in Bohemia, New York, had been awarded
a contract by the Federal Aviation Administration (FAA) to instrument 51 major U.S.
airports with Low Level Wind Shear Alert Systems (LLWAS). The Climatronics
proposal included the Model 05102 Wind Monitor as the system wind sensor. This
contract resulted in a blanket order for 450 Wind Monitors that, added to the require-
ments of other organizations, was cause for a major redesign effort to incorporate
numerous improvements that had been suggested by several different customers. One
of the most significant changes was the elimination of nearly all external screws and
set screws. The main mounting post and orientation ring were changed from machined
aluminum, fastened with set screws, to injection molded plastic with stainless-steel
band clamps for tightening on the standard 1-in. pipe. The entire nose cone assembly
and the main body of the sensor were now being injection molded while the tail
assembly continued to be fabricated by vacuum forming the white ABS plastic and
filling with foam. A simple internal spring latch was designed to secure the main
housing to the rotor of the mounting post assembly. The latch was accessed by
removing the nose cone assembly that was now threaded with an O-ring seal.
Previously, the nose cone was secured to the main housing with four screws. An
injection-molded junction box with a slide cover was added to the mounting post.
Special packaging was designed with die-cut foam fitted to a custom carton to provide
optimum protection during shipment. This latest design was introduced in August,
1984, and designated Model 05103 Wind Monitor (Fig. 6). A sensor interface circuit
and a 4- to 20-mA line driver circuit both with a choice of wind speed scaling in meters
per second, miles per hour, or knots and a choice of 360
or 540
azimuth range were
also made available to provide calibrated outputs for direct input into most recorders
and data loggers, and also for long cable runs.
768 COMMERCIAL RESPONSE TO MEASUREMENT NEEDS
5 ICING PROBLEMS
The FAA was very concerned about the performance and survivability of the LLWAS
Wind Monitor in icing conditions. A number of different ideas were tried for heating
the sensor, and several test programs were carried out both in a controlled laboratory
environment and in field conditions. A variety of commercially available wind
sensors were tested simultaneously. It was apparent that wet snow, clear ice, and
rime ice affected the performance and calibration of all mechanical wind sensors to
varying degrees. Snow had a greater effect on cup anemometers than on propeller
anemometers while both clear ice and rime ice caused degradation of performance of
both types. The physically larger anemometers were able to operate longer in icing
conditions before performance was badly deteriorated. Heating of rotating joints
allowed some sensors to operate longer before complete freeze-up; however, because
of loss of calibration with ice build up, the benefit of heating only rotating joints was
doubtful. Climatronics developed a heating scheme that utilized a heat element on
the sensor mounting pipe and an aluminum mounting post (in place of plastic) to
conduct some of the heat to the sensor bearings. It was felt that this provided some
benefit in helping the sensor to recover from freeze-up and was therefore adopted for
the LLWAS program. Our conclusion was that only heating the entire sensor assem-
bly with an array of heat lamps was sufficiently effective to warrant the cost. The heat
lamp array worked satisfact orily for low wind freezing rain events when tempera-
tures did not drop very far below freezing but was not useful for situations where
higher wind speeds and colder temperatures made the heating ineffective.
During the winter of 1983–1984 a Wind Monitor was installed on Mt. Washington
in New Hampshire to check on the effects of severe rime icing. During a prolonged
rime ice event with sustained winds, the sensor continued to operate reasonably well
due to the high rotation rate of the propeller, which prevented the rime ice from
adhering, and the continuous action of the vane, which prevented the rime ice from
bridging the gap between the vane skir t and the mounting post. After several hours
of high winds and rime ice buildup, the sensor failed when it was impacted by an ice
chunk that had dislodged from a structure up wind. From this test we concluded that
the Wind Monitor could operate effectively in light rime ice situations with contin-
uous wind but would probably not be suitable for heavy rime ice conditions.
6 WIDESPREAD ACCEPTANCE
Several organizations had been evaluating the Wind Monitor for some time. In 1984
Campbell Scientific in Logan, Utah, added it to its stand ard line of wind sensors and
began to place multiple orders. In 1985 The U.S. Army Atmospheric Sciences
Laboratory (ASL) at White Sands Missile Range began operational use of the
Wind Monitor and began purchasing multiple units through New Mexico State
University. Also in 1985 the National Oceanic and Atmospheric Administration
(NOAA)=Pacific Marine Environmental Laboratory (PMEL) began operational use
of the Wind Monitor for marine applications. Late in 1985 the National Data Buoy
6 WIDESPREAD ACCEPTANCE 769
Center began operational use of a special model of the Wind Monitor that was
modified for its application. About 2 years later further modifications, including a
machined aluminum mounting post, were made to provide NDBC a ‘‘ruggedized’’
version that could better withstand the rigors of buoy deployment in rough seas.
Units previously shipped to NDBC were also retrofitted with these modifications.
In the fall of 1985 a new model of the Wind Monitor was developed to meet the
requirements of the U.S. Environmental Protection Agency and the Nuclear Regu-
latory Commission for air pollution applications. This model utilized an expanded
polystyrene foam tail for greater sensitivity (improved damping ratio and lower
threshold). The polypropylene four-blade propeller was normally supplied; however,
an optional larger and lighter propeller was offered at additional cost. This optional
propeller was hand fabricated of carbon fiber and proved to be very popular.
We imported these from a supplier in France; however, the cost of hand fabrication
plus transportation and duty made them disproportionately expensive. The calibra-
tion of these propellers was also more variable than desired. Eventually we deve-
loped a much less expensive and more uniform injection-molded carbon fiber
thermoplastic propeller, which we manufacture in our own plant and supply as
standard. This second standard version of the instr ument is designated Model
05305 Wind Monitor-AQ (air quality model) (Fig. 4).
Figure 4 (Top) Model 05305 Wind Monitor-AQ (air quality model), February 1986.
(Bottom) Model 05701 Wind Monitor-RE (research model), July, 1987. See ftp site for
color image.
770
COMMERCIAL RESPONSE TO MEASUREMENT NEEDS
7 SPECIALIZED MODELS
In early 1985 we received another development contract from the Nat ional Data
Buoy Center to design a special model of the Wind Monitor with a tachometer
generator for the wind speed transducer. This model required the use of slip rings.
We calibrated the output of the tachometer generator so that it exactly matched the
output of the Bendix=Belfort sensors, which were the operational sensors at many
NDBC sites. With the addition of a special cable connector and special mounting
adapter fabricated at the NDBC facility, this special model Wind Monitor could
directly replace the other sensors in the field without any changes to the data
collection package. W hen we began making deliveries in December, 1985, we
designated this special-purpose Wind Monitor as Model 05203-1. It was only manu-
factured for NDBC plus a very few other customers for special applications. At a
later date we developed a low-power circuit that converted the frequency output of
the standard Wind Monitor into an analog voltage with the same calibration as the
tachometer generator version. The combination of the special circuit b ox plus a
standard Wind Monitor achieved the same result and was more reliable than the
special Model 05203-1.
8 DESIGN IMPROVEMENTS
The magnet and coil wind speed transducer had proved to be very reliable; however,
the signal level was very low when rotating slowly near threshold speeds providing a
marginal signal-to-noise ratio. In 1986 we changed the wire size in the coil from
26AWG to 4OAWG, allowing more than twice as many turns and a corresponding
increase in signal level. We were concerned about the durability of the much finer
wire, but field testing indicated that it was quite satisfactory. We invested in a special
coil winding machine that was able to properly control the tension and layering of
the finer wire on the special injection-molded bobbins. Also in 1986 we changed the
wind direction transducer to a custom-designed very high quality conductive plastic
potentiometer, custom manufactured to our own specifications. Previously we had
used potentiometers made by several different well-known manufacturers. These
were all standard-type conductive plastic potentiometers with modifications to
meet our requirements. While they all worked fairly well, the failure rate seemed
to be unacceptably high with many warranty replacements. The new custom poten-
tiometer, while much higher in initial cost, proved to be far more reliable and
therefore less costly due to reduced repair costs and greatly improved customer
satisfaction.
A fair ly large number of Wind Monitors were deployed by Pacific Gas and
Electric Company (PG&E) in a study of the dynamic thermal rating of power
transmission lines. In 1986 PG&E reported a problem with the wind speed signal
from an instrument located near a substation. The electromagnetic pickup from the
60-Hz power lines was causing a wind speed reading of about 6 mph when the actual
wind speed was at zero. This problem was solved by adding an RC low-pass filter
8 DESIGN IMPROVEMENTS 771
circuit that attenuated the 60-Hz signa l below signal conditioning trigger levels. The
circuit was designed to pass the normal ac wind speed signal at the very low
frequencies near threshold. It also passes the 60-Hz real wind speed signal, which
has a higher amplitude than the induced power line signal. This circuit has been
incor porated on all subsequent models.
In July, 1987, we introduced a third standard model of the Wind Monitor, which
was designed for maximum sensitivity for research and special applications
requiring measurement of very low wind speeds. The tail assembly is similar in
construction to the air quality model but with a much lower foam density, resulting
in an optimum damping ratio of 0.65. The very sensitive helicoid propeller is made
from the same expanded polystyrene foam as the tail, resulting in a very low thresh-
old and a short distance constant. This sensor, designated Model 05701 Wind
Monitor-RE (research model), is sold only in limited quantiti es (Fig. 4).
At the same time the different versions of the Wind Monitor (as well as other
products) were being developed, we were gaining valuable experience in injection
molding. We had acquired new CNC (Computer Numerical Control) machinery for
mold making and also new and larger injection-molding machines with better
controls and greater capability. In mid-1987 we completed a fairly sophisticated
mold to injection mold the entire tail assembly of the standard Wind Monitor.
This resulted in a much more uniform and durable tail assembly, which we could
produce at a significantly reduced cost.
By now many Wind Monitors, especially the Wind Monitor-AQ, were being used
in critical applications that required wind tunnel certification and field auditing.
From the first production runs all units were serial numbered; however, since the
propellers were interchangeable between sensors, in March, 1988, we began to serial
number all three types of production propellers. Previously, serial numbers were
added only to propellers that had been individually tested in our wind tunnel.
9 JUNIOR MODEL
In April, 1988, the National Data Buoy Center asked us to design a new reduced size
model of the Wind Monitor. Its buoys were becoming progressively smaller and it
was felt that a smaller sensor would be required in the future. All NDBC buoys use
duplicate wind sensors for redundancy. A smaller sensor would allow the two
sensors to be mounted far enough apart to avoid mutual interference while keeping
the sensors close enough to avoid damage during buoy deployment. The new smaller
Wind Monitor turned out to be about two-thirds the size of the standard model.
Prototypes were delivered in October, 1989, for field testing; however, this model
has not yet been deployed operationally by NDBC. This fourth standard model,
which was designated Model 04101 Wind Monitor-JR ( junior model) (Fig. 5),
was not advertised until November, 1993. Eventually it proved useful for several
special applications with a number of different customers and several hundred have
been produced to date.
772 COMMERCIAL RESPONSE TO MEASUREMENT NEEDS
10 CONTINUING DESIGN MODIFICATIONS
Until the spring of 1988 all Model 05103 Wind Monitors used ball bearings that had
light-contacting plastic seals and were lubricated with instrument oil. The Model
05305 Wind Monitor-AQ and Model 05701 Wind Monitor-RE use the same size ball
bearings but with noncontacting metal shields and instrument oil lubrication. This
combination provides lower threshold as required by agency specifications, but the
bearings are more easily contaminated and require routine maintenance. To achieve a
longer field life, the bearing lubrication in Model 05103 was changed from oil to a
special, wide-temperature-range grease. This resulted in a slight sacrifice in thresh-
old but provided a dramatic increase in service life, which was extremely valuable to
those customers with remote installations.
We had tested these sensors in our own wind tunnel and in the NDBC wind
tunnel and had established a gust survival specification of 80 m=s. We had also done
several sustained high-speed tests with the sensor mounted on a vehicle on an
extended highway trip. We were beginning to get inquiries regarding survival at
even higher wind speeds , especially for monitoring hurricane- and typhoon-prone
areas. In August, 1988, we were able to make arrangements to test a Model 05103
Wind Monitor in the NASA=AMES Research Center wind tunnel at Moffett Field,
Figure 5 (Top) Model 05103 Wind Monitor (standard model, shown for relative size).
(Middle) Model 04101 Wind Monitor-JR ( junior model), November, 1993. (Bottom) Model
04106 Wind Monitor-JR=MA ( junior marine model), October, 1994. See ftp site for color
image.
10 CONTINUING DESIGN MODIFICATIONS 773
California. In this test the sensor was installed in their 7 10 ft Wind Tunnel No. 1
and subjected to wind speeds that were stepped from 0 to 250 mph (110 m=s) and
back to 0 (in 12 steps). The wind tunnel was held for 2 min at each speed. The Wind
Monitor performed well throughout the entire speed range. With these data we
increased our gust survival specific ation to 100 m=s, and we began to recommend
the sensor for applications that required higher wind exposure.
Woods Hole Oceanographic Institution (WHOI) had tested and deployed many
Wind Monitors beginning with the early models. Beginning in March, 1989, WHOI
began to incorporate the Model 05103 Wind Monitor into its IMET (Improved
Meteorological Measurements from Buoys and Ships) ‘‘intelligent’’ sensor program.
To satisfy its requirements, we had to adapt the upper portion of the sensor to a
specially designed base assembly that WHOI supplied to us. The potentiometer,
normally supplied for the wind direction transducer, was omitted and an elongated
coupling was provided for connection to an optical encoder located in the special
base assembly along with the signal conditioning and data logger circuits. Several of
these units have been built and successfully field tested on buoys and research
vessels by WHOI in an ongoing program. This same type of sensor package is
now being proposed for the new NOAA=Voluntary Observing Ship (VOS) program,
which may eventually include 300 to 400 vessels.
During the next several months additional design changes were made to improve
performance and to overcome some reported field problems. The junction box,
which contained the terminal strip for cable connections, was enlarged to accom-
modate a printed circuit board with transient protection devices. The circuit board
also mounted an improved device for cable connections. There had been a number of
potentiometer failures in the field that occurred during thunderstorm activity and
also similar failures associated with extremely dry and windy sites such as the
Antarctic. After extensive testing in our engineering department, we discovered
that the terminations of the conductive plastic element in the potentiometer were
susceptible to failure when a static charge would build up on the housing . Two
changes were made to combat this problem. A ground wire was added to the housing
of the potentiometer and connect ed directly to the earth ground terminal in the
junction box. In addition the molded plastic parts surrounding both the coil and
the potentiometer were changed to a conductive-type plastic. The mounting post was
also changed to conductive plastic. With these changes and a properly grounded
installation the static discharge failures were almost completely eliminated.
11 TESTING & CERTIFICATION
The World Meteorological Organization (WMO) had scheduled an intercomparison
study of wind instruments to take place between July, 1992, and October, 1993. The
Swiss Meteorological Institute (SMI) was already familiar with the Wind Monitor
and recommended that we include it in the study. We submitted an application
through the U.S. National Weather Service (NWS) to include the Model 05103
Wind Monitor, which was accepted. The WMO Wind Instrument Intercomparison
774 COMMERCIAL RESPONSE TO MEASUREMENT NEEDS
was conducted jointly by METEO-FRANCE and the Swiss Meteorological Institute.
The test site was the Mont Aigoual Observatory in the Cevennes Mountains in
southern France. The observatory is at an altitud e of 1567 m and normally experi-
ences strong winds and heavy rime ice conditions during winter. The Wind Monitor
was installed and operated satisfactorily without maintenance during the entire study,
including winter, except during several periods of heavy rime ice. During the ice
events the sensor became frozen and ceased to function; however, upon thawing it
recovered and again functioned within specifications. The final report was released
by METEO-FRANCE in October, 1997. We were sur prised and pleased to learn
that, after careful data analysis, the Wind Monitor had been selected as the reference
sensor for the study. As the results of the intercomparison became known, there was
a marked increase in acceptance of the Wind Monitor in Europe.
Late in 1992, to update our wind tunnel transfer standards, we arranged to have a
Model 05103 Wind Monitor (with a four-blade polypropylene propeller) and a
Model 05305 Wind Monitor-AQ (with a four-blade carbon fiber thermoplastic
propeller) tested at the National Institute of Standards and Technology (NIST) in
Gaithersburg, Maryland. Both models were run in the NIST 1.5 2.1 m (5 7 ft)
Dual Test Section Wind Tunnel (DTSWT) from 0 to 46 m=s (103 mph) as well as the
NIST Low Velocity Facility (LVF) from 0 to 10 m=s (22 mph). Based upon the data
from these tests we found that the calibration of the four-blade polypropylene
propeller differed from our published calibration by approximately 1%. The calibra-
tion of this propeller can be shifted slightly during manufacture by altering injection-
molding temperature and pressure. Therefore we were able to correct the slight
discrepancy in calibration. Unfortunately, the four-blade carbon fiber thermoplastic
propeller used on the Model 05305 Wind Monitor-AQ exhibited a calibration
discrepancy of 4.5%. The material used in the manufacture of this propeller does
not allow any adjustment during the molding process. It was therefore necessary to
publish a new calibration for this model and advise our customers of the revision.
Fortunately many custo mers were able to apply a correction factor to their data to
improve its quality.
12 MARINE MODEL
The number of Wind Monitors being used in marine applications was steadily
increasing and in April, 1993, we introduced a standard model that incorporated
many of the special modifications that we had done for the National Data Buoy
Center. The sealed ball bearings are lubricated with a special waterproof grease. The
junction box, normally attached to the mounting post, is omitted and a 3-m (10 ft)
heavy-duty cable is supplied with a waterproof cable gland. The surge suppression
components are contained in a potted module with the cable connections inside the
mounting post. This fifth standard sensor is designated Model 05106 Wind Monitor-
MA (marine model) (Fig. 6). The following year we introduced a marine version of
the Wind Moni tor-JR that incorporated the same special modifications. The Model
12 MARINE MODEL 775