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Input Signal
f = 90 Hz
Threshold = 0 V
Hysteresis = 200 mV
Triggering Stage
Pulse Generator
Filtered Output
Triggering Stage
Input signals that do not pass through 0 V, such as digital pulse trains, do not meet
Note
the triggering requirements and cannot be measured.
© National Instruments Corporation
Refer to Figure 3 as you read the following sections.
+100 mV
0 V
–100 mV
5 V
0 V
5 V
0 V
9 V
0 V
This stage consists of a trigger circuit that compares the input waveform to
a fixed threshold and hysteresis to create a square-shaped pulse for the next
stage.
The purpose of hysteresis is to reduce the number of false triggers caused
by noise. In order to be measured and trigger the pulse generator, the
amplitude of the input signal must exceed V
and both the maximum and the minimum peaks must lie outside the
hysteresis range. The threshold for the SCC-FV01 is fixed at 0 V and the
hysteresis is fixed at 200 mV. This means the amplitude of the input signal
must be at least ±100 mV
±100 mV hysteresis range in order for the signal to be measured (refer to
the first section of Figure 3). To ensure maximum accuracy, use an input
signal of amplitude 200 mV
The maximum input range is ±10 V. You can extend the input range
by using an analog input module as the first stage of a dual-stage
configuration. For example, the SCC-AI02 module has a gain of 0.5
and isolation. If you use an SCC-AI02 as the first stage, you increase the
Figure 3. Input Channel Stages
THRESHOLD
and the peaks must lie on each side of the
pk
(400 mV
) or greater.
pk
p-p
11
SCC-FV01 Frequency Input Module User Guide
± 1/2 V
,
HYSTERESIS
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