Siemens SIMATIC S7-1200 System Manual page 563

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SDT: HSC_Period

The "HSC_Period" data type corresponds to an HSC configured for "Period" mode. The

CTRL_HSC_EXT instruction provides program access to the number of input pulses over a

specified measurement interval. This instruction allows for the time period between input

pulses to be calculated with a fine nanosecond resolution.

HSC_Period structure

Structure element Declaration

ElapsedTime returns the time, in nanoseconds, between the last counting events of

sequential measurement intervals. If no counting events occurred during a measurement

interval, ElapsedTime returns the cumulative time since the last counting event.

ElapsedTime has a range from "0" to 4,294,967,280 nanoseconds (0x0000 0000 to 0xFFFF

FFF0). The return value 4,294,967,295 (0xFFFF FFFF) indicates that period overflow has

occurred. Overflow indicates that the time between pulse edges is greater than 4.295

seconds and the period cannot be calculated using this instruction. The values from 0xFFFF

FFF1 to 0xFFFF FFFE are reserved.

EdgeCount returns the number of counting events received during the measurement interval.

The period can only be calculated when the value of EdgeCount is greater than zero. If

ElapsedTime is either "0" (no input pulses received) or 0xFFFF FFFF (Period overflow), then

EdgeCount is not valid.

When EdgeCount is valid, use the following formula to calculate the period in nanoseconds:

Period = ElapsedTime/EdgeCount

The calculated time period value is an average of the time periods of all of the pulses that

occur during the measurement interval. If the period of an incoming pulse is greater than the

measurement interval (10, 100, or 1000 ms), then the period calculation requires multiple

measurement intervals.

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK

See description below.

See description below.

Enables the HSC for Period measurement when true; disables

Period measurement when false.

Enables NewPeriod value to take effect.

Specifies the measurement interval time in milliseconds. The

only allowed values are 10, 100 or 1000 ms.

Technology instructions

10.1 Counting (High-speed counters)