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How the FM 450-1 Counts
2.1
Definitions
What is Counting?
2
Count Range,
Count Limits
Load Value
Comparison
Values
Example
Three Different
Counting Methods
2-2
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Counting refers to the process of capturing and summing up events. In the
case of the FM 450-1 function module, encoder signals are captured and eva-
luated accordingly.
The FM 450-1 can count up and down. By selecting the count range, you
define the limits within which the FM 450-1 can count.
Count Range
Count range 1: 32 bits
Count range 2: + 31 bits
You can specify a starting value to the FM 450-1 for each of the two count-
ers. Counting starts at this value. The starting value is referred to as the load
value. The load value can be any value within the count limits.
In order to be able to trigger responses in the process independently of the
CPU when a specific counter status is reached, you can use two of the mo-
dule's digital outputs for each counter. You store two comparison values on
the FM 450-1 for each counter. If the counter status reaches either of the two
comparison values, the digital output assigned to the comparison value is set
and/or a process interrupt is generated.
In the example in Section 1.2, the motor for conveyor belt B is to be stopped
as soon as the carton contains the programmed number of parts. For this pur-
pose, you can specify this number to the FM 450-1 as the comparison value
for counter 1, for example, and use the assigned digital output to stop the
motor.
With the FM 450-1, you can count rectangular pulses in three different ways:
Continuous counting, with or without gate function
Single count, with hardware or software gate
Periodic counting, with hardware or software gate
The differences between the methods become obvious in the behavior of the
FM 450-1 when a counter has reached a count limit.
Lower Count Limit
0
+ 4,294,967,295
– 2,147,483,648
+ 2,147,483,647
FM 450-1 Counter Function Module
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Upper Count Limit
C79000-G7076-C450-01
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