Interval Counter Input
4-3
SM 335 – High-Speed Analog Input/Output Module for the SIMATIC S7-300
6ES7 335-7HG00-8BA1
4.2
Principles of measuring with the interval counter
Purpose
Pulses from a simple sensor are acquired via an interval counter input. The sensor
might, for example, be located on the barrel extruder of an injection molding ma-
chine. You can determine the rotational speed of the barrel from the interval bet-
ween the 2 pulses.
Principle
The SM 335 measures the amount of time (time interval) that passes between two
pulses. The SM 335 determines the interval with a resolution of 0.5
m
s. The num-
ber of intervals measured is also tallied.
If you know the number of pulses the sensor generates for each revolution of the
barrel extruder, you can compute the speed, at which the barrel extruder rotates.
Example
N = 16 pulses are generated per barrel extruder revolution (N is also referred to as
the sensor’s number of pulses per revolution). The interval between two pulses is
50,000 increments. The rotational speed of the barrel extruder is thus computed as
follows:
v
+
1
T·N
+
1
50000·0.5
m
s·16
+
2.5 rps
+
150 rpm
Lower limiting value
The interval duration counter returns a 3-byte value, enabling representation of up
to FF FF FF
H
(16777215 in decimal representation). For N = 1, the critical fre-
quency thus computes to:
v
+
1
T·N
+
1
16777215·0.5
m
s
+
0.1192.5rps
+
7, 15rpm
