The Boolean block can monitor the state of a tank by turning on a siren on the plant floor if a problem arises. For example, suppose that the following conditions indicate a problem:
As these diagrams illustrate, a problem could be identified if either of two situations is true. The first situation requires that two conditions be true: the motor is on and the level is low. The second situation requires that only one condition be true: the operator has put the unit on hold.
Using these conditions, you would create a database block to monitor each condition. DI1 to monitor the motor, AI1 to monitor the level, and DOHOLD to place the tank on hold.
Once you create these blocks, you can use the Boolean block to send a True (1) or False (0) signal to a Digital Output block, ALMDO, by entering these blocks as input to the Boolean block and specifying an equation. If the equation evaluates to true, the block sends a 1 to ALMDO and the siren is turned on. If the equation is false, the block sends a 0 to ALMDO and the siren remains turned off.
