Period value measurement
The terminal offers the option of calculating and outputting the period value in addition to the counter value.
The following limit values apply to the determination of measured values:
Measured value output | Measured value limit | Comment | |
|---|---|---|---|
lower | top | ||
Period value | 0.20 µs | 21 s | With 4-fold evaluation |
1 µs | 21 s | With 4-fold evaluation | |
Period value measurement sequence (Period value)
- For the period value measurement, the time between two positive edges of input A is measured with a resolution of 10 ns.
- In each case the last period within the PLC cycle is considered and output as separate process data in index 0x6000:14 "Period value".
- "Period scaling" (index 0x8000:14) indicates the resolution of the output period value. The default value is 10 ns. Alternatively the period value can be output in the unit 100 ns (0x8000:14 "Period scaling" set to 100dec) or 500 ns (0x8000:14 "Period scaling" set to 500dec).
- If no full period is detected within a PLC cycle (two positive edges of input A), the last valid value is output.
- The period measurement continues across cycles. As soon as a new value is available, the process data is updated in index 0x6000:14 "Period value".
- If no full period is detected within 21 seconds, the measurement is discarded and the output in index 0x6000:14 "Period value" is set to the maximum value, 2147483648.
Fig.165: Period value measurement
Fig.166: Period value measurement for long periods | Difference frequency and period value measurement The period value is recalculated for each cycle and output in the process data. The frequency measurement always averages the measured periods over a timeframe. The "Period value" is therefore a current value, the "Frequency value" is an averaged value. |