Campbell 21X Instrukcja Operatora Pobierz pdf (Strona 67)

SECTION

7. MEASUREMENT

PROGRAMMING

EXAMPLES

7.7

ANEMOMETER

WITH

PHOTOCHOPPER

OUTPUT

An anemometer with

a

photochopper

transducer

produces

a

pulsed

output which

is monitored

with

the Pulse

Count Instruction,

configured for

High Frequency

Pulses. The

anemometer

used

in

this example is the

R.M. Young

Model No.

12102D

Cup Anemometer which

has

a 10

window

chopper

wheel.

The

photochopper

circuitry is

powered

from

the 21X

or 21XL

12V

supply.

Supplemental charging,

AC

or solar,

should

be used

with

the 21XL.

lf a

charging

source is not

practical,

back-up

batteries

should

be used

to compensate for the increased

current

drain.

Wind

speed is desired

in

meters

per

second.

There

is

a

pulse

each time a window

in

the

chopper

wheel,

which

revolves

with the

cups,

allows light

to

pass

from

the source

to

the

photoreceptor.

Because there are 10

windows

, A

in the

chopper wheel, there are t0

pulses per

I

'6

revolution.

Thus, 1 rpm is

equalto 10

pulses

per

60 seconds

(1

minute)

or 6 rpm

=

1

pulse

per

second. The manufacturer's

calibration for

relating

wind speed to rpm is:

Wind speed

(m/s)

=

0.01632

m/s/rpm

x rpm

+ 0.2 m/s

Pulse

count instruction has the

option of

converting

counts

to frequency

in Hz

(counts/second).

The multiplier

and

offset to

conveft Hz

to meters

per

second

are:

m/s

=

0.01632

m/s/rpm

x

6

rpm/Hz

x XHz

+ 0.2 m/s

=

0.0979 mls/Hz x XHz +

0.2 m/s

There

are times when the 21X is not

able to

reset

the

pulse

counters at the exact

time

interval

programmed.

lf

the artificially large wind

speed

that results from a long interual

is

used,

it

causes a false

average or

maximum

value. To

avoid this,

the 21X

is instructed

to discard

values

resulting

from

long intervals

and use

the

previous

value instead.

7-4

ANEMOMETER

SUPPLY

GROUND

AND SIGNAT REFERE

PULSE

OUI

01: P3

01: 1

02: 1

r03:

20

04: 10

05:

06:

FIGURE

7.7-1.

Wiring Diagram for

Anemometer

PROGRAM

Pulse

Rep

Pulse Input

Chan

High frequency;

Output

Hz.

Loc

[:WS

m/s

1

.0979 Mult

.2 Otfset

TIPPING

BUCKET

RAIN

GAUGE

WITH

LONG

LEADS

A tipping bucket

rain

gauge

is measured

with

the Pulse

Count

Instruction

configured for

Closure.

Counts

from

long intervals will be

(an

option in Parameter 3),

as

the

final

output

desired is

total

rainfall

(obtained

with lnstruction

T2,Totalize).

lf

counts from long intervals

were

discarded,

less

rainfallwould

be

recorded than

was actually measured by the

gauge

(assuming

there were

counts

in

the long intervals).

Output

is desired in millimeters of

precipitation.

The

gauge

is

calibrated

for a 0.01 inch tip;

a

multiplier

of 0.254

is used.

CONNECTIONS

3OO, LEAD

LENGTH

FIGURE 7.8-1.

Wiring

Diagram for Rain

Gauge

with

Long Leads

In a long

cable

there is appreciable

capacitance

between the lines,

which is

discharged across

the

switch when

it closes. In

addition to

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