Campbell CR23X Spécifications télécharger pdf (Page 100)

SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES

7-12

2: BR Transform Rf[X/(1-X)] (P59)

1: 6 Reps

2: 1 Loc [ Vs_Vx_1 ]

3: .1 Multiplier (Rf)

3: Polynomial (P55)

1: 6 Reps

2: 1 X Loc [ Vs_Vx_1 ]

3: 1 F(X) Loc [ Vs_Vx_1 ]

4: .15836 C0

5: 6.1445 C1

6: -8.4189 C2

7: 9.2493 C3

8: -3.1685 C4

9: .33392 C5

7.14 NONLINEAR THERMISTOR IN

HALF BRIDGE (CAMPBELL

SCIENTIFIC MODEL 101)

Instruction 11, 107 Thermistor Probe,

automatically calculates temperature by

transforming the millivolt reading with a 5th order

polynomial. Instruction 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 polynomial fit has been determined.

In this example, the CR23X is used to measure

the temperature of 5 Campbell Scientific 101

Probes (used with the CR21). Instruction 4,

Excite, Delay, and Measure, is used because the

high source resistance of the probe requires a

long input settling time (see Section 13.3.1).

The signal voltage is then transformed to

temperature using the Polynomial Instruction.

The manual for the 101 Probe gives the

coefficients of the 5th order polynomial used to

convert the output in millivolts to temperature (E

denotes the power of 10 by which the mantissa

is multiplied):

C0 -53.7842

C1 0.147974

C2 -2.18755E-4

C3 2.19046E-7

C4 -1.11341E-10

C5 2.33651E-14

The CR23X will only allow 5 significant digits to

the right or left of the decimal point to be entered

from the keyboard. The polynomial cannot be

applied exactly as given in the 101 manual. The

initial millivolt reading must be scaled if the

coefficients of the higher order terms are to be

entered with the maximum number of significant

digits. If 0.001 is used as a multiplier on the

millivolt output, the coefficients are divided by

0.001 raised to the appropriate power (i.e.,

C0=C0, C1=C1/0.001, C2=C2/.000001, etc.).

With this adjustment, the coefficients entered in

Parameters 4-9 of Instruction 55 become:

C0 -53.784

C1 147.97

C2 -218.76

C3 219.05

C4 -111.34

C5 23.365

CR23X

FIGURE 7.14-1. 101 Thermistor Probes

Connected to CR23X

PROGRAM

1: Excite-Delay (SE) (P4)

1: 5 Reps

2: 24 1000 mV, 60 Hz Reject,

Slow Range

3: 1 SE Channel

4: 1 Excite all reps w/Exchan 1

5: 10 Delay (units 0.01 sec)

6: 400 mV Excitation

7: 1 Loc [ V_1 ]

8: 1.0 Mult

9: 0.0 Offset

2: Polynomial (P55)

1: 1 Reps

2: 1 X Loc [ V_1 ]

3: 1 F(X) Loc [ V_1 ]

4: -53.784 C0

5: 147.97 C1

6: -218.76 C2

7: 219.05 C3

8: -111.34 C4

9: 23.365 C5

1 2 ... 95 96 97 98 99 100 101 102 103 104 105 ... 373 374

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Campbell CR23X Spécifications Page 100

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