NI cDAQ-9178 - Page 50

NI cDAQ-9178/9174 User Guide and Specifications 50 ni.com
Use this type of measurement to count events or measure the time that occurs between edges on
two signals. This type of measurement is sometimes referred to as start/stop trigger measurement,
second gate measurement, or A-to-B measurement.
Refer to the following sections for more information about the NI cDAQ-9178/9174 edge-separation
measurement options:
• Single Two-Signal Edge-Separation Measurement
• Implicit Buffered Two-Signal Edge-Separation Measurement
• Sample Clocked Buffered Two-Signal Separation Measurement
Single Two-Signal Edge-Separation Measurement
With single two-signal edge-separation measurement, the counter counts the number of rising
(or falling) edges on the Source input occurring between an active edge of the Gate signal and an active
edge of the Aux signal. The counter then stores the count in the FIFO and ignores other edges on its
inputs. Software then reads the stored count.
Figure 42 shows an example of a single two-signal edge-separation measurement.
Figure 42. Single Two-Signal Edge-Separation Measurement
Implicit Buffered Two-Signal Edge-Separation Measurement
Implicit buffered and single two-signal edge-separation measurements are similar, but implicit buffered
measurement measures multiple intervals.
The counter counts the number of rising (or falling) edges on the Source input occurring between an
active edge of the Gate signal and an active edge of the Aux signal. The counter then stores the count in
the FIFO. On the next active edge of the Gate signal, the counter begins another measurement. The
USB-STC3 transfers the sampled values to host memory using a high-speed data stream.
AUX
Counter
Armed
8
0000123 456788 8
Measured Interval
GATE
SOURCE
Counter Value
Latched Value