Campbell CR23X Especificações descarregar pdf (Página 205)

SECTION 13. CR23X MEASUREMENTS

13-5

For the rising case, V

= V

-V

, whereas for

the decaying transient, V

= V

Substituting these relationships for V

Equations 13.3-1 and 13.3-2, respectively,

yields expressions in V

, the input settling error:

= V

-t/R

, rise [13.3-6]

= V

e'o

-t/R

, decay [13.3-7]

Where V

e'o

= V

-V

, the difference between

the peak transient voltage and the true signal

voltage.

NOTE: Since the peak transient, V

causes significant error only if it is several

times larger than the signal, V

, error

calculations made in this section

approximate V

e'o

by V

; i.e., V

= V

-V

If the input settling time constant, τ , is known, a

quick estimation of the settling error as a

percentage of the maximum error (V

for

rising, V

e'o

for decaying) is obtained by knowing

how many time constants (t/τ) are contained in

the 450 µs CR23X input settling interval (t).

The familiar exponential decay relationship is

given in Table 13.3-1 for reference.

TABLE 13.3-1. Exponential Decay, Percent

of Maximum Error vs. Time in Units of τ

Time % Time %

Constants Max. Error

0 100.0 5 0.7

1 36.8 7 0.1

3 5.0 10 0.004

Before proceeding with examples of the effect

of long lead lengths on the measurement, a

discussion on obtaining the source resistance,

, and lead capacitance, C

L, is necessary.

CR23X

FIGURE 13.3-2. Typical Resistive Half Bridge

CR23X

HI OR LO

INPUT

FIGURE 13.3-3. Source Resistance Model for Half Bridge Connected to the CR23X

1 2 ... 200 201 202 203 204 205 206 207 208 209 210 ... 373 374

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Campbell CR23X Especificações Página 205

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