Data Translation DT9834 Series, Руководство пользователя

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Principles of Operation
101
Frequency Measurement
Use frequency measurement mode if you want to measure the number of rising edges that
occur on the Counter
n Clock input over a specified duration.
You can connect a pulse of a known duration (such as a one-shot output of another user
counter) to the Counter
n Gate input signal. Use software to set up the counter/timers as
follows:
1. Set up one of the counter/timers for one-shot mode, specifying the clock source as
internal, the clock frequency, the gate type that enables the operation as rising edge or
falling edge, and the polarity of the output pulse as high-to-low transition or low-to-high
transition of the output pulse.
2. Set up the counter/timer that will measure the frequency for event counting mode,
specifying the type of clock pulses to count and the gate type (this should match the pulse
output type of the counter/timer set up for one-shot mode).
3. Start both counters (pulses are not counted until the active period of the one-shot pulse is
generated).
4. Read the number of pulses counted. (Allow enough time to ensure that the active period
of the one-shot occurred and that events have been counted.)
5. Determine the measurement period using the following equation:
Measurement period = 1 * Active Pulse Width
Clock
Frequency
6. Determine the frequency of the clock input signal using the following equation:
Frequency Measurement = Number of Events
Measurement
Period
Edge-to-Edge Measurement
Use edge-to-edge measurement mode if you want to measure the time interval between a
specified start edge and a specified stop edge.
The start edge and the stop edge can occur on the rising edge of the Counter n Gate input, the
falling edge of the Counter n Gate input, the rising edge of the Counter n Clock input, or the
falling edge of the Counter n Clock input. When the start edge is detected, the counter/timer
starts incrementing, and continues incrementing until the stop edge is detected. The C/T then
stops incrementing until it is enabled to start another measurement. When the operation is
complete, you can read the value of the counter.
You can use edge-to-edge measurement to measure the following:
• Pulse width of a signal pulse (the amount of time that a signal pulse is in a high or a low
state, or the amount of time between a rising edge and a falling edge or between a falling
edge and a rising edge). You can calculate the pulse width as follows:
−
Pulse width = Number of counts/18 MHz