Hello Experts,

I need a diagnostic bit to inform me when the CPU (S7-1500) is in STOP mode. The FB "LED" is working when CPU is in RUN mode only.

Is necessary excecated this FB in separate OB?

Thanks

Thanks for your replies.

I know how to produce an alarm if the PLC is stopped (via watchdog logic).

My topic focused if SIEMENS has a FB (or something else) in order to produce this alarm for STOP mode. 

For example the LED FB is not "correct" because refer the Run/ Stop mode but in reality LED is always run (due to in stop mode the LED FB is not executed.

Thanks

AutoGen_2199634

Thanks for your replies.

I know how to produce an alarm if the PLC is stopped (via watchdog logic).

My topic focused if SIEMENS has a FB (or something else) in order to produce this alarm for STOP mode. 

For example the LED FB is not "correct" because refer the Run/ Stop mode but in reality LED is always run (due to in stop mode the LED FB is not executed.

Thanks

Are you asking for some code to run on the PLC while the PLC is in STOP mode? User code is not allowed to run at all when the PLC is in STOP mode. 

If you have an FB that toggles a digital bit, be it internal M-bit, DB bool tag, or digital output, once the PLC is in STOP, (as already stated), the FB ceases to execute, and that digital bit will cease to toggle.

If there is another device connected to the Siemens PLC and sharing direct digital data (digital output to digital input for example), or via S7 DB exchange, or via Siemens S7-1500 sending data using a TCP, UDP, MB_TCP, or other method, many of those will stop sending automatically.

Without a watchdog bit included in any data exchange where the PLC is actively toggling, some remote devices will not be aware the comms have stopped.

However, if the remote device has a timer timing between S7-1500 data sends (like the NDR output of most S7-1500 comm blocks, for "new data received"), it will know when the S7-1500 has stopped sending when the timer reaches a predefined value. 

That time-out preset could be:

• 3-5x max time between updates
• Predefined timer timeout preset value, like 5 sec
• Results of an engineering calculation for max time remote device can be out of touch (with the s7-1500) before it must react to a loss of comms with the s7-1500, to save the process, or stop waiting for the s7-1500 and perhaps empty / run out the system, or stop allowing entry into the system

PLC logic is incapable of detecting STOP mode because the logic stops running.

However, there is a way in hardware to configure a digital output to fire when the PLC is in STOP, and while the PLC is running, the logic forces that digital output to OFF.

By using 2 mostly static DigOuts, you can inform outside devices whether the PLC is running or stopped, or powered off.

Configure DigOut A to fail ON, and DigOut B to fail OFF

In PLC Logic, configure DigOuts as follows:

    A      B
  -----  -----
   OFF    ON

State table for DigOut A & B:
  A      B   MEANING
-----  ----- ---------------------------
  OFF   OFF  PLC STOPPED, LOSS OF POWER
  OFF   ON   PLC STOPPED, POWERED UP
  ON    OFF  PLC RUNNING
  ON    ON   PLC RUNNING, BUT DIG OUT B FAILED OR MODULE LOST POWER

With this setup, the remote device or system can immediately react appropriately to each situation, without any of the delays associated with watchdog fault detection.

Most systems should avoid being this tightly bound, but if they are, this is a way to avoid watchdog fault detection delay.

There are other ways, but this is easy and simple to understand, explain, and deal with.

AutoGen_2199634

Thanks for your replies.

I know how to produce an alarm if the PLC is stopped (via watchdog logic).

My topic focused if SIEMENS has a FB (or something else) in order to produce this alarm for STOP mode. 

For example the LED FB is not "correct" because refer the Run/ Stop mode but in reality LED is always run (due to in stop mode the LED FB is not executed.

Thanks