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EX1200-1538: Counter/Timer Operation
27
Here, the period is determined using consecutive,
non-overlapping
samples.
If
and for every
N
th
cycle,
= Measured period for each cycle
= Average count
= Number of cycles occurred
x
= Averaging window count
Pulse Width Measurements
Pulse Width
measurements measure the duration of an input signal’s high cycles (T
HC
). The
EX1200-1538 only measures the time between a positive and negative slope. Thus, to determine a
high cycle’s duration, the polarity parameter should be set to
Normal
(high). To measure an input
signal’s low cycle, the polarity must be set to
Inverted
(low). As a result, both measurements
cannot be performed simultaneously.
NOTE
Positive cycle width and negative cycle width cannot be measured simultaneously. However, by
using two separate channels, one for measuring positive cycle width and other one for measuring
low cycle width, this limitation can be surmounted
As a derivative of the
Period
function, pulse width measurements use the same averaging
methodologies (i.e.,
Aperture Time
and
Average Count
mode). The implementation of these
methods is shown in the figures below.
Aperture
Window Start
Aperture
Window End
T
1
T
2
T
3
T
4
T
5
Aperture Window
T
6
T
HC
= (T
1
+ T
2
+ T
3
+ T
4
+ T
5
+ T
6
)/6
Availability of
Measurement Result
F
IGURE
3-12:
P
ULSE
W
IDTH
M
EASUREMENT
U
SING
A
PERTURE
T
IME
A
VERAGING
Measurement Result 1, T
HC
= (T
1
+T
2
+T
3
)/3
Measurement Result 2, T
HC
= (T
2
+T
3
+T
4
)/3
Measurement Result 3, T
HC
= (T
3
+T
4
+T
5
)/3
Measurement Result 4, T
HC
= (T
4
+T
5
=T
6
)/3
Averaging
automatically
starts on the first
raising edge
Averaging Window 4
T
1
T
2
T
3
T
4
T
5
T
6
Averaging Window 3
Averaging Window 2
Averaging Window 1
F
IGURE
3-13:
P
ULSE
W
IDTH
M
EASUREMENT
(A
VERAGE
R
EPEAT
=
F
ALSE
)
