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Using input periods


    The ABNs have a sophisticated new feature (available from firmware version 3.5) which we call 'input periods'. This differs from input delays in that this is basically a 'switch debouncing' feature.

    Although when a switch is opened or closed we would expect current to flow or not flow, this is not the case in the real world. Switch or relay contacts often 'bounce' when opening or closing which results in a number of pulses on the line. This could be construed by the ABN to be a number of contact closures happening in rapid succession. Similarly, in electrically noisy environments, short spikes on the line could also be interpreted to be contact closures.

    To deal with this problem, the ABNs have a feature known as 'input periods'. What this does is to ensure that an input has been constantly at either a high or low voltage level for a specific period of time before the ABN considers that input to have been triggered.

    The default period for which an input must be activated is 0.5 second. This means that a contact closure for shorter period than 1/2 second will not be recognized by the ABN. However, this period may be changed by the user.

    For example, a user may have connected a pushbutton to an input and only wish to have the input triggered if the button is pushed for a full three seconds. This may be useful to avoid inadvertent triggering of the input.

    In this example, assuming the pushbutton is connected to input M, we could set the trigger period by issuing the command:


    'M', of course, refers to input 'M', and '30' means that the input period is to be 30 1/10ths of a second, or 3 seconds.

    Note that there must always be TWO digits in this command to avoid confusion with the 'input delay' command. So, set input 'M' back to the default input period of 1/2 second, we would issue the command:


    where 5 1/10ths of a second gives a 1/2 second period. Don't forget the leading zero!

    Another example may be that we want input 'J' to react very quickly to events. Then we may send the following command:


    which will ensure that input J will trigger within 1/10th of a second of activation.