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Section 3-7
+'
3. In case of Circular Mode (refer to 3-2-2 "Circular Mode" for more information),
the Rate Value calculated after a Rollover, will be corrected to take this Rollover
into account.
Rate History Log File
The Rate Values, which are calculated during consecutive Time Windows, are
stored in the Rate History Log File inside the Unit. The Rate History Log File can
contain a maximum number of 64 most recent Rate Values.
The Rate Values can be read into your Ladder Program for further usage, by issu-
ing an IORD-instruction. Like this, one or multiple Rate Values (with a maximum of
64) can be read. If you specify to read only one Rate Value the youngest Rate
Value will be returned. If the Rate History Log File is full a new (youngest) Rate
Value will overwrite the oldest Rate Value. Refer to 4-5-3-2
for detailed information.
Frequency Measurement
After the Rate Value is read into the Ladder Program this value can be used to cal-
culate the Frequency [Hz] of the applied signals. The Frequency of the incoming
pulses can be calculated by using the following formula:
If for example the Time-Window is set to 2 seconds (= 2000 ms) and during the
Time-Window 20,000 up counts are received (i.e. Rate Value = 20,000) the corre-
sponding Frequency is 10,000 Hz.
Rotational Speed
Measurement
After the Rate Value is read into the Ladder Program this value can also be used
to calculate the Rotational Speed [rpm]. The Rotational Speed can indicate the
speed of a motor in rotations per minute [rpm]. The Rotational Speed can be cal-
culated by using the following formula:
If you want to calculate the Rotational Speed you need to know the number of
Pulses per motor or encoder revolution [P/R]. If for example the Time-Window is
set to 1 second (= 1000 ms), the Encoder Resolution is 2,000 P/R and during the
Time-Window 50,000 up counts are received (i.e. Rate Value = 50,000) the corre-
sponding Rotational Speed is 1,500 rpm.
Rate History Log File:
Oldest Rate Value
Youngest Rate Value
(The Rate Values occupy 2 words each)
Rate Value 1
Rate Value 2
Rate Value 3
Rate Value R
R <= 64
Frequency [Hz] =
Rate Value
Time-Window [s]
Rotational Speed [rpm] =
Rate Value
Encoder Resolution [P/R]
Time-Window [s]
60
W902-E2-03.book Seite 84 Donnerstag, 7. Oktober 2004 2:06 14
Summary of Contents for CS1W-CT021
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