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grig100
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Joined: 01 Jan 2015
Posts: 752
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 Posted: 21/05/2019 20:01 Post subject: How do you calculate the operating time in STEP 7 TIA Portal |
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How do you calculate the operating time for a terminal device (pump, for example) in STEP 7 (TIA Portal)?
https://support.industry.siemens.com/cs/document/52258130/how-do-you-calculate-the-operating-time-for-a-terminal-device- (pump-for-example)-in-step-7-(tia-portal)
You calculate the operating time for a terminal device by reading out the current data and the current time of the CPU and calculating the difference between the two times.
Fig. 1 shows an example for calculating the operating time for a terminal device. For this, STEP 7 (TIA Portal) provides the two extended instructions "RD_SYS_T" (read time) and "T_DIFF" (time difference). The output of the calculated time is then the difference between the data read and thus the operating time for the device.
Fig. 1
The library in the entry includes the FB "Timedifferent" with an SCL program in which the "RD_SYS_T" instruction is called conditionally twice in succession.
When the input parameter "startTime" has the signal"0", the first condition is fulfilled and the first instruction "RD_SYS_T" is executed.
When the input parameter "stopTime" has the signal "0", the second condition is fulfilled and the second instruction "RD_SYS_T" is executed.
The IF instructions are followed by the call of the "T_DIFF" instruction. Fig. 2 shows an example for the call of the FB "Timedifferent" in the OB "Main"
Instructions for determining the operating time for the terminal device:
| Code: | Step 1: "startTime" = "0" and "stopTime" = "0"
The two "RD_SYS_T" instructions simultaneously read out the current date and the current time of the CPU. In this way the difference between the two times calculated with the "T_DIFF" instruction is zero.
The value of the output parameter "outTime" of the "T_DIFF" instruction is reset to zero.
Step 2, start of time measurement: "startTime" = "1" and "stopTime" = "0"
The first "RD_SYS_T" instruction is not executed and thus reading of the CPU clock is interrupted. The last value read from the CPU clock is stored in a static variable.
The second "RD_SYS_T" instruction continues to be active and the current data is stored in a second static variable.
The difference between the time values of the two static variables is calculated with the "T_DIFF" instruction and stored in the output variable "outTime".
Step 3, end of time measurement: "startTime" = "1" and "stopTime" = "1"
The first "RD_SYS_T" instruction continues not to be executed. The last value read from the CPU clock remains stored in a static variable.
The second "RD_SYS_T" instruction is also no longer executed and thus, here too, reading of the CPU clock is interrupted. The last value read from the CPU clock remains stored in a static variable.
The difference between the two time values is calculated with the "T_DIFF" instruction. The result is then transferred as the operating time to the output parameter "outTime".
Note
Before a new time measurement can start you first have to reset the two parameters "startTime" and "stopTime" to zero. |
The table below shows the input and output parameters with the associated data types of the FB "Timedifferent".
https://support.industry.siemens.com/cs/mdm/109755202?c=88772662795&lc=en-WW
https://support.industry.siemens.com/cs/attachments/52258130/52258130_Timedifferent_Lib_STEP7_TIA_Portal_V13.zip
https://support.industry.siemens.com/cs/attachments/52258130/52258130_Timedifferent_Lib_STEP7_TIA_Portal_V15.1.zip |
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