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3.5 Measurement Time and
Measurement Ranges
3.5.1 General
Selection of MEASURE RATE (SLOW, MEDIUM,
and FAST) obviously relates to measurement time,
providing the user with an easily made choice. (The
slower rates provide greater accuracy.) Programming
a DELAY (typically because the normal setting time
is insufficient for a particular handler or biasing rou-
tine) also obviously affects measurement time. In this
paragraph, the many items that affect measurement
time are explained. The measurement time (required
to complete a measurement and display the results)
depends not only on the selected measure rate, and
programmed delay, but also on the presence or ab-
sence of the high-speed measurement option, test
conditions, choice of display, whether data is being
sent out to other devices, etc. The best combination
of conditions for any particular job should be selected
recognizing their effects on speed and accuracy. The
following examples are representative; some of the
numbers are approximate.
NOTE: Except where stated otherwise (as in para-
graph 3.5.10), measurement time is given for the
condition that the "quick acquisition" special function
is NOT selected. So accuracy is as specified. (See
page xiii at the front of the manual.)
1693 Digibridge. The minimum measurement time
is about 34 ms (30 meas/sec). The corresponding
conditions are: measure rate = fast, IT factor set to
0.25 (integration time factor - paragraph 3.5.5), test
frequency = 10 kHz to 100 kHz, display selection =
bin no., measure mode = continuous (which elimi-
nates the settling time that is normal with triggered
mode), no data output via IEEE-488 bus.
For test frequency = 1 kHz, the minimum is about 44
ms (23 measurements per second).
Surprisingly Long Times. Please be aware of the long
time periods that can be required by this very fast
measuring instrument.
Operation
NOTE: Under some conditions, testing can consume
so much time that the opera tor might wonder whether
the Digibridge is really operating. See below.
The longest single measurement cycle (including
programmable delay set to 99999 ms and the special-
function selection of "median value") is about 5
minutes. The Digibridge will execute up to 255 full-
length cycles if you select maximum averaging, for
a total of about 22 hours from START to display of
measured result.
3.5.2 Measure Rate Selection at
Keyboard
Choose one of 3 basic measurement rates with the
[MEASURE RATE] key: SLOW, MEDIUM, or
FAST. The continuous-mode rates are respectively
about 1, 4, and 8 measurements per second, if the
other test conditions and programmable selections
are left at normal power-up defaults.
The tradeoff is speed vs. accuracy. The Digibridge
will make a more precise and accurate measurement
at a slower rate. For the above conditions, in very
simplified terms, the basic accuracy is 0.02%, and
the tradeoff is as follows:
• SLOW rate: 1 measurement per second, 0.02%
accuracy (or better);
• MEDIUM rate: 4 measurements per second,
0.05% accuracy (or better);
• FAST rate: 8 measurements per second, 0.12%
accuracy (or better).
For details on accuracy, refer to the specifications.
In the accuracy formulas, the effect of measure rate
selection appears as the term "Ks."
1693 RLC Digibridge
45
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