NI C Series Getting Started

where
■
f
x
is the frequency of the input signal
■
N
periods
is the number of signal periods measured
■
f
k
is the counter timebase frequency
You can calculate the maximum frequency error using the following equation:
Measurement Frequency Error ( Hz ) = f
x
×
f
x
( N
periods
× f
k
) - f
x
For example, when measuring the frequency of a 1 MHz input signal with the divisor
count of 10, and the counter timebase of 100 MHz, the maximum error is
1 MHz
(10 × 100 MHz ) - 1 MHz
× 100 % = 0.1 %
The maximum frequency error is
1 MHz ×
1 MHz
(10 × 100 MHz ) - 1 MHz
= 0.001 MHz
The resulting measured frequency is 1 MHz ± 0.001 MHz.
Note This error does not include the error introduced by the timebase
accuracy.
Trigger Settings
Counter Arm—You can control when the counter starts the frequency measurement
through the counter arm control. Aer the counter is armed, it waits for the active
edge on the signal-to-measure, and then it begins measuring the signal period. The
measurement data is only ready and valid once the counter has finished measuring
the first measurement according to the Divisor and Measurement Time settings. The
counter returns a value of zero for both the N
ticks
and N
periods
times prior to the first
measurement becoming ready. Refer to your soware documentation for more
information on arming the counter.
Pulse Width Measurement
You can take pulse width measurements with the NI-9361.
The counter measures and returns the duration of a pulse on a signal. The NI-9361
returns the current pulse width measurement value when the counter is read. The
measurement values consist of the pulse width duration of the signal-to-measure in
© National Instruments
21
NI-9361 Getting Started

NI C Series Specifications

General

Brand	NI
Model	C Series
Category	Control Unit
Language	English