National Instruments DAQCard-1200 User Manual page 50

Chapter 3 Signal Connections
DAQCard-1200 User Manual
Pulsewidth measurement is performed by level gating. The pulse you want
to measure is applied to the counter GATE input. The counter is loaded with
the known count and is programmed to count down while the signal at the
GATE input is high. The pulse width equals the counter difference (loaded
value minus read value) multiplied by the CLK period.
Perform time-lapse measurement by programming a counter to be edge
gated. An edge is applied to the counter GATE input to start the counter.
You can program the counter to start counting after receiving a low-to-high
edge. The time lapse since receiving the edge equals the counter value
difference (loaded value minus read value) multiplied by the CLK period.
To perform frequency measurement, program a counter to be level gated
and count the number of falling edges in a signal applied to a CLK input.
The gate signal applied to the counter GATE input is of known duration. In
this case, you program the counter to count falling edges at the CLK input
while the gate is applied. The frequency of the input signal then equals the
count value divided by the gate period. Figure 3-18 shows the connections
for a frequency measurement application. You can also use a second
counter to generate the gate signal in this application. In this case, program
the second counter for a one-slot mode. This configuration requires an
external inverter to make the output pulse of the second counter active high.
3-28 © National Instruments Corporation