Campbell Scientific CR10 CR10 Measurement and Control - Page 98

SECTION

7.

MEASUREMENT

PROGRAMMING

EXAMPLES

01:

P5

01:

6

02:

15

03:

1

04;

1

05:

2500

06:

1

07:

1

08:

0

PROGRAM

AC

Half Bridge

Reps

2500

mV

fast

Range

lN Chan

Excite

all

reps

dEXchan

1

mV Excitation

Loc

[:H20

BARS

]

Mult

Offset

BR

Transform

Rf[)0(1

-X)]

Reps

Loc

[:H20

BARS

]

Multiplier

(Rf)

Polynomial

Reps

X

Loc H20 BARS

F(X) Loc

[:H20

BARS

]

.15836

C0

6.1445

C1

-8.4189

C2

9.2493

C3

-3.1685

C4

.33392

C5

7.15

NONLINEAR THERMISTOR

IN

HALF

BRTDGE

(MODEL

101 PROBE)

lnstruction

11,

107

Thermistor

Probe, automatically

linearizes the output

of

the

nonlinear

thermistor

in

the

107 Probe by transforming

the

millivolt reading

with a 5th order

polynomial.

lnstruction

55,

Polynomial,

can

be used to calculate temperature of

any nonlinear thermistor, provided the correlation

between temperature and probe output is known,

and an appropriate

polynomialfit

has been

determined.

ln this example,

the

CR10 is used

to

measure the temperature

of

five

101 Probes

(

with the CR21 but usually

not

the CR10).

4,

Excite, Delay, and Measure, is used because

high

source

resistance of

the

probe requires

a

input settling

time

(Section

12.3.1).

The

voltage

is

2000

mV,

the

same as used

in

the

The

signalvoltage

is

then transformed to

temperature using

the

Polynomial Instruction.

The

manual for

the

101 Probe gives the

of

the 5th order polynomial used to convert the

output in millivolts

to

temperature

(E denotes

power

of

10

by which

the

mantissa is multiplied)

-53.7842

0.147974

-2.18755E-4

2,',t9046E-7

-1.11341E-10

2.336s1E-14

The CR10

willonly

allow 5 significant digits to

or left

of

the decimal point

to

be

entered from

keyboard.

The

polynomialcannot

be applied

as given

in

the

101

manual. The

initial millivolt

reading must be scaled

if

the coefticients

of

the

order terms are

to

be entered with

the

maxi

number of significant

digits.

lf

0.001

is used as

multiplier on

the

millivolt output, the coefficients

divided by 0.001 raised to the appropriate

C0=C0,

C1

=Cl

/0.001,

C2=C21.000001, etc.).

this

adjustment, the coefficients entered in

Parameters 4-9

of

Instruction

55

become:

-53.784

147.97

-218.76

219.05

-111.34

23.365

02:

01:

02:

03:

03:

01:

02:

03:

o4:

05:

06:

o7:

08:

09:

c0

c1

c2

c3

c4

cs

P59

6

1

.1

P55

6

I

I

1

c0

c1

c2

c3

c4

c5

THERMISTOR PROBES

H1

cR1

0

LI

H2

L2

HJ

G

RED LEADS

TO

SINGLE

ENDED

INPUT

CHANNELS

1-5

7-14

FIGURE

7.15-1.

101

Thermistor

Probes

Connected

to CRl0

Campbell Scientific CR10 CR10 Measurement and Control - Page 98

Nonlinear Thermistor, Model

Page 98 highlights