National Instruments AT-MIO-64F-5, User Manual

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Configuration and Installation Chapter 2
AT-MIO-64F-5 User Manual 2-34 © National Instruments Corporation
4.7 k
W
Signal
Source
Switch
33
DIG GND
Counter
OUT
SOURCE
GATE
+5 V
MIO Subconnector
AT-MIO-64F-5 Board
Figure 2-17. Event-Counting Application with External Switch Gating
To perform pulse-width measurement, a counter is programmed to be level gated. The pulse to
be measured is applied to the counter GATE input. The counter is programmed to count while
the signal at the GATE input is either high or low. If the counter is programmed to count an
internal timebase, then the pulse width is equal to the counter value multiplied by the timebase
period.
For time-lapse measurement, a counter is programmed to be edge gated. An edge is applied to
the counter GATE input to start the counter. The counter can be programmed to start counting
after receiving either a high-to-low edge or a low-to-high edge. If the counter is programmed to
count an internal timebase, then the time lapse since receiving the edge is equal to the counter
value multiplied by the timebase period.
To measure frequency, a counter is programmed to be level gated and the rising or falling edges
are counted in a signal applied to a SOURCE input. The gate signal applied to the counter
GATE input is of some known duration. In this case, the counter is programmed to count either
rising or falling edges at the SOURCE input while the gate is applied. The frequency of the
input signal is then the count value divided by the known gate period. Figure 2-18 shows the
connections for a frequency measurement application. A second counter can also be used to
generate the gate signal in this application.