Fast digital signals are not detected in the controller
I have the prolem that, some signals form operator button are not detected in the controller, if the operator touch the button realy fast. I read the signals in a 10ms task in the controller. I can see the LED on the DI-Card but the signal is not reaching the controller. The IO-Card is connected to the controller over profibus.
Does anybody has similar problem whith fast digital signals?
Used Hardware secification:
Controller: AC800PEC (task 10ms)
Profibus: CI854 (Baudrate: 1.5M)
Voted best answer
Profibus comms is not synchronous with your PLC task and operates substantially slower than 10ms. As you have found, operators can easily beat the speed settings of the bus. Speeding up your program will not help. If you want hi speed digital inputs like this you need to use a modulebus IO connection direct to the CPU - In which case the IO will be syncronized to the program scan time.
Alternatively use a push button that has a minimum contact time Or slow release. For applications like a rotation sensor where push buttons cannot be used and the pulse time is short then modulebus is your only option.