Campbell Scientific CR10 CR10 Measurement and Control - Page 151

SECTION

11.

OUTPUT PROCESSING INSTRUCTIONS

r**

69

WIND

VECTOR

***

FUNCTION

Instruction

69

processes

the

primary variables

of

wind

speed and direction

from

either

polar

(wind speed and direction) or

orthogonal

(fixed

East

and

North propellers)

sensors.

lt

uses

the

raw data

to

generate

the

mean wind speed,

the

mean wind

vector

magnitude, and

the

mean

wind vector direction over an output interval.

Two different calculations of wind

vector

direction (and standard deviation of wind

vector

direction) are available, one

of

which

is

weighted for wind speed.

When

used

with

polar sensors,

the

instruction

does

a

modulo divide by 360 on wind direction,

which allows the wind direction

(in degrees)

to

be

0

to 360,

0

to 540,

less than 0, or greater

than

540.

The ability

to

handle a negative

reading is useful in

an

example where a ditficult

to

reach wind

vane

is improperly oriented and

outputs

0

degrees at

a

true

reading of 340

degrees.

The

simplest solution

is

to enter an

offset of

-20

in

the

instruction measuring the

wind vane,

which

results in

0

to

360 degrees

following

the

modulo divide.

When

a

wind

speed

sample

is

0,

the

instruction

uses 0

to

process scalar

or

resultant

vector

wind speed and standard deviation, but the

sample is not used

in

the

computation of wind

direction. The

user may

not

want

a sample less

than

the

sensor

threshold

used

in

the

standard

deviation.

lf

this

is

the case

instruction 89 can

be

used to check

wind

speed, and if less than

the

threshold,

Instruction 30 can set

the

input

location

equalto

O.

Standard deviation

can

be processed one of

two

ways:

1) using every sample taken during

the

output

period (enter

0

for

parameter 2),

or,

2) by averaging standard deviations processed

from

shorter

sub-intervals

of

the

output

period.

Averaging sub-interval standard deviations

minimizes

the

effects

of

meander under light

wind conditions,

and

it provides more complete

information

for

periods

of

transition'

.

t

EPA

On-site

Meteorological Program

Guidance

for

Regulatory Modeling Applications.

Standard deviation

of

horizonlal wind

fluctuations

from sub-intervals

is

calculated as

follows:

o(o)=[((oo1

l2+(c@2)2

...+(

oo")z;/vt1

t

rz

where

o(@) is

the

standard deviation over the

output

interval, and

o@1

...o@u are

sub-interval

standard deviations.

PARAM.

DATA

NUMBER

TYPE

DESCRIPTION

01:

2

Repetitions

02:

4

Samples

per sub-

interval

(number

of

scans, enter

0

for

no

sub-interual)

03:

2

Sensor/Output2digits:

AB

A

Sensortype:

0

=

Speed and

Direction

1

=

East and North

B

Output option:

0

S,

@1,

o(@1)

1

s,01

2

S,

U,

@u,

o(@u)

04:

4

First wind speed

inPut

location no. (East wind

speed)

05:

4

First wind direction

input location

no.

(North wind speed)

Outputs

Generated: 2-4

(depending on output

option)

for each

repetition

A

sub-interval

is specified as

a

number

of

scans.

The

number of scans

for

a sub-interval

is

given

by:

Desired

sub-interval

(secs)

/ scan

rate (secs)

In

an example where

the scan

rate is

1

second

and

the Output

Flag is set every

60

minutes,

the

standard

deviation

is

calculated

from

all 3600

scans when

the sub-interval

is

0.

With

a sub-

intervalof

900

scans

(15 minutes)

the

standard

deviation

is

the

average

of

the

four

sub-interval

standard

deviations.

The last

sub-interval

is

weighted

if

it

does

not contain

the

specified

number of scans.

1

1-1

Campbell Scientific CR10 CR10 Measurement and Control - Page 151

Output Processing Instructions

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