Siemens SIMATIC S5-100U, System Manual

Page: 248 / 552

Integrated Blocks and Their Functions S5-100U
9.2.5 Analog Value Conditioning Modules FB250 and FB251
Function block FB250 reads in an analog value from an analog input module and outputs a value XA
in the scale range specified by the user.
Function block FB251 allows you to output analog values to analog output modules. Values from the
range between the “UGR” (lower limit) parameters and the “OGR” (upper limit) parameters are
converted to the nominal range of the selected module.
You will find more information on the following topics in section 11.6:
• Calling up and setting parameters in FB250.
• Calling up and setting parameters in FB251.
• An example of analog value processing with FB250 and FB251.
9.3 Integrated Organization Blocks
9.3.1 Scan Time Triggering OB31, for CPU 103 and Higher
A scan time monitor monitors the program scan time. If program scanning takes longer than the
specified scan monitoring time, the CPU goes into the STOP mode. This can happen when one of
the following errors occurs:
• The control program is too long.
• The program enters a continuous loop.
You can retrigger the scan time monitor at any point in the control program by calling up OB31.
Calling up this block restarts the scan time monitor.
Call up OB31
• Prerequisite: SYSTEM COMMANDS “YES” has been specified on the programmer.
• JU OB31 can be programmed at any point in the control program.
Programming
One statement in OB31 is sufficient, e.g. “BE” to make the retriggering effective. Other
statements are also possible.
9.3.2 Battery Failure OB34
The CPU constantly checks the status of the battery in the power supply. If a battery fails (BAU),
OB34 is processed before every cycle until the battery is replaced. You can program the reaction of
the programmable controller to battery failure in OB34. If OB34 is not programmed, there is no
reaction.
9-14
EWA 4NEB 812 6120-02b