Omron CJ1W-CT021 Operation Manual page 106

Extra Functions
Rate History Log File
Frequency Measurement
Rotational Speed
Measurement
86
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.
Oldest Rate Value
Youngest Rate Value
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 "Rate History Log File
data" for detailed information.
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.
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:
Rotational Speed [rpm] =
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:
Rate Value 1
Rate Value 2
Rate Value 3
Rate Value R
(The Rate Values occupy 2 words each)
Rate Value
Frequency [Hz] =
Time-Window [s]
Rate Value
Encoder Resolution [P/R]
Section 3-7
R <= 64
60
Time-Window [s]