Delayed, Debounced and Intermittent Timers and Triggers
Sometimes a regular timer or trigger is not sufficient for the task. A delayed trigger may be needed to debounce a signal or flash a delayed output. How about intermittently flashing a light or siren or warning a user on the HMI? The human brain tends to eventually ignore continuous states. A blinking light or an on/off siren is more likely to alert an operator than a steady signal.
Then there is the combination of both with a delayed, but intermittent, signal. Think of a low priority warning or a timer based air blow during machine run. All of these can be done using a combination of Beckhoff's built in
F_TRIG function blocks. However, it would be easier to have a function block that has all of this functionality in one neat package. Meet
It works with both a rising edge or a falling edge by providing an input for both. There are also two
time inputs to specify the debounced and intermittent delay times.
Using both rising and falling edge detection in the same FB can lead to undefined behavior!!
|INR||Rising edge input|
|INF||Falling edge input|
Here are the outputs. It can be used as a basic trigger or timer with
QET respectively, but also allows all the extra functionality mentioned above.
|QT||Normal trigger. Will pulse after WT elapsed|
|QET||Normal timer. Will turn on after WT + PT elapsed|
|QDT||Delayed trigger. Will pulse after WT + PT elapsed|
|QIT||Intermittent trigger. Will pulse after WT elapsed then again after every PT elapsed|
FUNCTION_BLOCK TON_TRIG VAR_INPUT INR : BOOL; INF : BOOL := TRUE; WT : TIME; PT : TIME; END_VAR VAR_OUTPUT QT : BOOL; QET : BOOL; QDT : BOOL; QIT : BOOL; END_VAR VAR tm : TON; td : TON; tr : R_TRIG; reset : BOOL := TRUE; END_VAR td(IN := INR OR NOT INF, PT := WT); tm(IN := NOT tm.Q AND td.Q, PT := PT); tr(CLK := td.Q); IF QDT THEN QDT := FALSE; reset := FALSE; END_IF IF tm.Q THEN IF reset THEN QDT := TRUE; END_IF QET := TRUE; ELSIF NOT INR AND INF THEN QET := FALSE; reset := TRUE; END_IF QT := tr.Q; QIT := QT OR tm.Q;
It's a simple FB, but it gets the job done and is always nice to have handy when dealing with timers and triggers.