Hello,

I am currently working on a program for an Siemens S7-1200 PLC, I need to monitor the states of a few analog inputs, and in case that they do not get to a preset value within a specified time, I need to stop the program execution and change an output value (essentially stopping a motor).

My idea so far is to use a Time delay interrupt and hopefully reset the time delay every time my analog input is at a satisfactory level, so the interrupt will only occur IF the time expires, and some hardware will have failed. My issue is, I am not sure how I can reset the timer after I have invoked the SRT_DINT block, or whether I can just invoke SRT_DINT on the same block?

If you have any help with this idea, or an alternative way to achive the functionallity it will be much appreciated.

Thanks in advance,

- Rolf

Alright, so if I want to reset the time, before the interrupt has actually occured, I can just invoke the start Again with the same time, and the time before the interrupt occurs will be reset?

Ah alright, thank you, do you (or anyone else for that matter) then have any idea what happens if I invoke SRT_DINT on a previously started time delayed interrupt (But before the first interrupt has occured).

I.e. do I overwrite the time in the timer register, essentially setting a new time for the interrupt, or is it a queue so now two interrupts will occur?

William_B

RRoos

Ah alright, thank you, do you (or anyone else for that matter) then have any idea what happens if I invoke SRT_DINT on a previously started time delayed interrupt (But before the first interrupt has occured).

I.e. do I overwrite the time in the timer register, essentially setting a new time for the interrupt, or is it a queue so now two interrupts will occur?

The interrupt is triggered from the moment it detected a transition. When you make a new transition you will have updated to a new schedule.

 Well as I understand, that is the behavour of a regularly interrupt, for example trigged by an external even on an input port.

What I am looking for is internally triggered interrupts based on a timer, and then being able to reset the same timer in order to delay the interrupt further, and by doing this aiming at a similar functionallity as the watchdog timer on µCs, so essentially the interrupt only occurs if something goes wrong at run-time.

Alright, that makes sense, so based on your first suggestion, every time your invoke SRT_DINT, det delay_time will be overwritten incase the interrupt has not yet occured, right?

Concerning the cyclic interrupt, how does that code 'cancel' the interrupt incase the pistons moves within the correct time parameter?

Thanks alot for your help so far, I think i'm going with the time_delay interrupt however, as I do not realy need µs precision, as I purely need to shut off a motor incase something has failed. As the system is relatively slow, a timer of a few seconds is fine.