Campbell 21X Manual do Operador descarregar pdf (Página 71)

SECTION

7. MEASUREMENT

PROGRAMMING

EXAMPLES

The

relationship

between

temperature

and PRT

resistance

is a slightly

nonlinear one. Instruction

16 computes

this relationship

for

a

DIN

standard

PRT

where the nominaltemperature

coefficient

is

0.00385/oC. The

change

in

nonlinearity

of a

PRT

with

the

temperature

coefficient of

0.00392/oC is

minute

compared with

the

slope

change.

Entering a slope

correction factor

of

0.00385/0.00392

=

0.98214

as

the

multiplier in

Instruction 16

results

in a calculated

temperature which

is

wellwithin the

accuracy

specifications

of the PRT.

PROGRAM

01: Po

01: 1

02: 1

03:

3

04: 1

05: 5000

06:

11

07: .001

08:

.02344

o2:

01:

02:

03:

11

50

P16

1

11

12

.98214

0

Full Bridge

Rep

5 mV

slow

Range

lN

Chan

Excite

all

reps

w/EXchan

1

mV

Excitation

Loc

[:Rs/RO ]

Mult

Offset

BR

Transform Rf[)V(1

-X)]

Rep

Loc

[:Rs/RO ]

Multiplier

(Rf)

Temperature RTD

Rep

R/Ro Loc Rs/RO

Loc

[:TEMP

degO]

Mult

Offset

P59

1

03:

01:

02:

03:

Q4:

05:

7.12

PRESSURE TRANSDUCER

-

4

WIRE FULL BRIDGE

This

example describes

a measurement made

with

a Druck

PDCR

10/D

depth

measurement

pressure

transducer. The

pressure

transducer

was

ordered

with

passive

temperature

compensation for

use with

positive

or negative

excitation

and

has

a

range

of 5

psi

or

about 3.5

meters

of water. The

transducer

is

used to

measure

the depth of water

in a stilling well.

Instruction

6,

4 Wire Full

Bridge, is used

to

measure

the

pressure

transducer. The

high

output

ol the semiconductor

strain

gauge

necessitates the

use

of the 50mV

input

range.

The

sensor

is calibrated

by connecting it

to the

01:

01:

02:

03:

Q4:.

05:

06:

07:

08:

7-8

21X

and

using lnstruction

6 with

a multiplier of

and

an offset of 0, noting

the

readings

("6

with

10 cm of

water

above the

sensor and with

334.6 cm of water

above the sensor. The

of Instruction 6 is 1000

Vr/V* or millivolts

per

volt

excitation. At 1O

cm the

reading

is

0.19963mV4/ and at 334.6 cm the reading

is

6.6485mV4/.

The multiplier to

yield

output in

is:

(334.6

-

10)/(6.6485-.19963)

=

50.334

cm/mV

The

offset

is

determined

after

the

pressure

transducer

is installed

in

the

stilling well. The

sensor is

installed

65 cm

below

the water level

at the time of

installation. The

depth of water at

this time

is

determined

to be

72.6 cm relative to

the desired reference. When

programmed

with

the multiplier determined

above

and

an offset

0,

a

reading of

65.12 is obtained.

The

offset

for

the actual

measurements

is thus determined to

be72.6

-

65.12

=

7.48 cm.

The lead length is

approximately

10 feet,

so

there is no appreciable error due to lead wire

resistance. Example

7.13 shows a means of

compensating

for long

lead

lengths.

CONNECTIONS

PRESSURE TR

FfGURE 7.12-1.

Wiring

Diagram

for Full

Bridge Pressure Transducer

P6

1

3

1

1

5000

1

50.334

7.48

PROGRAM

Full Bridge

Rep

50 mV slow Range

lN Chan

Excite all reps

dEXchan

mV

Excitation

Loc

[:WATER

cm

]

Mult

Offset

1 2 ... 66 67 68 69 70 71 72 73 74 75 76 ... 190 191

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