Campbell Scientific CR10 CR10 Measurement and Control - Page 94

+.,

SECTION

7.

MEASUREMENT

PROGRAMMING

EXAMPLES

nonlinearity of

a

PRT with the

temperature

coefficient of

0.00392/"C

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

Full Bridge

01:

1

Rep

02: 21

2.5

mV

60

Hz rejection Range

03:

3

lN Chan

04:

1

Excite

all

reps

w/EXchan

1

05:

2500

mV Excitation

06: 11

Loc

[:Rs/Ro

]

O7:

0.001

Mult

08:

.02344

Offset

02: P59

BR

Transform Rfl)V(1-X)l

01:

1

Rep

O2: 11

Loc

[:Rs/Ro

]

03: 50

Multiplier (Rf)

=P17qg

03: P16

Temperature

RTD

01:

1

Rep

02: 11

F/Ro

Loc Rs/Ro

03: 12

Loc

[:TEMP

C

]

04:

.98214

Mult

05: 0

Offset

7.12

PRESSURE

TRANSDUCER

.4

WIRE FULL

BRIDGE

This example

describes a

measurement made

with

a

Druck PDCR 930

depth

measurement

pressure

transducer. The

pressure

transducer

was ordered

for

use with

5

volt

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.

lnstruction

6,

4

Wire

Full Bridge, is used

to

measure

the

pressure

transducer. The

high

ou

of

the semiconductor strain gage necessitates

use

of

the

25

mV input

range.

The

sensor

is

calibrated

by

connecting

it

to the CR10 and

Instruction 6, an excitation voltage of 2500

mV,

multiplier

of

1

and an offset of 0, noting

the

readings

(.6

Mode)

with

10

cm

of

water above

sensor and with 334.6 cm

of

water above the

sensor.

The output

of

Instruction

6 is

1000

V

or

millivolts per volt

excitation. At

10

cm

the

reading

is

0.19963 mVA/ and

at

334.6 cm the

reading

is

6.6485

mV

/.

The

multiplier to yield

output

in

cm

is:

(334.6

- 10y(6.648s-.19963)

=

50.334

cm/mV/t/

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 of

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.

01:

01:

02:

03:

04:

05:

06:

07:

08:

P6

1

23

1

1

2500

1

50.334

7.48

Full Bridge

Rep

25

mV

60

Hz rejection

lN

Chan

Excite

all

reps

w/EXchan

1

mV Excitation

Loc

[:HT

cm

]

Mult

Offset

TRANSDUCER

PRESSURE

E1

R10

H1

LI

AG

7-10

FIGURE

7.12-1. Wiring

Diagram

for

Full Bridge

Pressure

Transducer

Campbell Scientific CR10 CR10 Measurement and Control - Page 94

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