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National Instruments Corporation
15
NI SCC-CTR01 User Guide and Specifications
Using the NI SCC-CTR01
The NI SCC-CTR01 is functional in a variety of applications including
counting events; pulse width, period, semi-period, position, and frequency
measurements; and frequency, pulse, and pulse train generation.
The variation between the LOW to HIGH and the HIGH to LOW
propagation delays on the input channels may affect semi-period or
pulse-width measurements. Adjusting the measurement by the difference
between the LOW to HIGH and the HIGH to LOW propagation delays
(typically 30 ns at 5 V operation) minimizes this effect, as illustrated by
the following equation for a positive pulse in positive logic:
Example:
If using typical LOW to HIGH and HIGH to LOW propagation
delays/relays (180 ns and 150 ns), and the actual measured pulse
width is 820 ns, then
Adjusted Pulse Width
= 820 ns + (180 ns – 150 ns) = 820 ns.
The variation between the switching times on the output channel can affect
duty cycle generation. Adjusting the output by the difference between the
LOW to HIGH (220 ns) time and the HIGH to LOW time (120 ns)
minimizes this effect.
Example:
While using the typical LOW to HIGH and HIGH to LOW times, if the
actual desired duty cycle is 0.50 at 400 kHz then:
Adjusted Duty Cycle
= 0.50 + (150 ns – 500 ns)
×
400 kHz = 0.36.
Adjusted Pulse Width
Actual Measurement
LOW to HIGH Delay HIGH to LOW Delay
–
(
)
.
+
=
Adjusted Duty Cycle
Desired Duty Cycle
Low to
High
High to Low Time
–
(
)
Frequency of Generation
.
×
+
=
