5: S
PECIAL
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AXIS P
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ANUAL
FT9Y-B1378
Frequency Measurement
This section describes frequency measurement, which measures the frequency of pulses input to an external input. Frequency
measurement is a function that measures the frequency of pulses input to an external input.
These input pulses are processed with dedicated hardware device in SmartAXIS, so frequencies can be measured with no relation
to the scan time. Groups that do not use frequency measurement can be used as normal inputs, high-speed counters, catch input,
and interrupt input. The measurement results are stored in special data registers and they are updated with each scan.
Function Specification
The SmartAXIS external inputs are used by switching between normal input, high-speed counters, catch input, interrupt input, and
frequency measurement. To use frequency measurement, specify the relevant group as Frequency Measurement in the
WindLDR Function Area Settings.
The frequency measurement results are stored in the following special data registers (Read-only):
Notes:
• If the input pulse cycle is longer than the scan time, the measurement results are updated at pulse cycle + 1 scan time.
• The data registers for the upper word and the lower word of the measurement value change according to the 32-bit data storage method
specified. For details, see "32-bit Data Storage Setting" on page 5-62.
Applicable Models
• The AC power type does not support frequency measurement. In situations where the frequency measurement function is required, use the
DC power type.
• Of the DC power types, only the the 24-, 40-, and 48-I/O types can use external inputs I6 and I7 for frequency measurement. The 12-I/O
type cannot use external inputs I6 and I7 as the frequency measurement function.
Group 123456
External input I0 I2 I3 I5 I6 I7
Frequency measurement
value (32 bits)
Upper word D8050 D8056 D8062 D8068 D8134 D8140
Lower word D8051 D8057 D8063 D8069 D8135 D8141
Frequency measurement range 1 Hz to 100 kHz 200 Hz to 100 kHz
Measurement error
Less than ±1%
(Truncated after the decimal point)
Calculation cycle Each scan time
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