Keithley KPCI-3101 Series, Руководство пользователя

Страница: 45 / 146

KPCI-3101 — KPCI-3104 Series User’s Manual Principles of Operation 2-25
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 1ms.) In this configuration, frequency is determined
using the following equation:
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 2-13 .
Figure 2-13
Connecting frequency measurement signals (shown for clock input 0 and
external gate 0)
In this configuration, use DriverLINX 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 fre-
quency, gate type, type of output pulse (high or low), and pulse width.
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:
Determine the frequency of the clock input signal using the following equation:
Frequency Measurement
Number of Events
Duration of the Windows Timer
----------------------------------------------------------------------------- =
STA-300 Panel
TB26
Signal Source TB29
TB28
Gate 0
TB31
User
Counter
Output 1
TB25
Digital Ground
User Clock Input 0
Measurement period
1
Clock Frequency
-----------------------------------------
Active Pulse Width
×
=
Frequency Measurement
Number of Events
Measurement Period
------------------------------------------------- =