Data Translation DT300 Series, Руководство пользователя, Страница: 100 / 164

Chapter 6
100
In this configuration, use software to specify the counter/timer mode as frequency
measurement or event counting, and the duration of the Windows timer over which to
measure the frequency. (The Windows timer uses a resolution of 1 ms.) In this configuration,
frequency is determined using the following equation:
Frequency Measurement = Number of Events
Duration of the Windows Timer
If you need more accuracy than the Windows timer provides, you can connect a pulse of a
known duration (such as a one-shot output of another user counter) to the external gate input,
as shown in
Figure 36 .
Figure 36: Connecting Frequency Measurement Signals
(Shown for Clock Input 0 and External Gate 0)
In this configuration, 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, clock
frequency, gate type, and type of output pulse (high or low).
2. Set up the counter/timer that will measure the frequency for event counting mode,
specifying the clock source 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 (events are not counted until the active period of the one-shot pulse is
generated);
4. Read the number of events 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
STP300 Panel
TB26
Signal Source TB29
TB28
Gate 0
TB31
User
Counter
Output 1
TB25
Digital Ground
User Clock Input 0