Honeywell EXCEL 5000 User Manual page 264

EXAMPLES
74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)
The curve formula for Manual operation is:
day = -8*(TW-3.99)-12
Where TW is the analog point representing TF26.
The following diagram represents the control loop and switching logic tables that
implement this example:
The TF26 temperature selector is represented by the point "ess".
The MAT icons incorporate the formulas for the Auto and Day modes of operation.
The auto formula supplies the correction signal that must be added to the setpoint of
Time Program to generate the corrected setpoint. The day formula supplies the
correction signal that must be added to the constant day setpoint (20C [68F]) to
generate the corrected setpoint.
However, the formulas cannot be used as-is because the mathematical editor does
not permit two operations in direct succession (in this example, =-8 where the
equals sign is followed by the minus sign).
To create acceptable formulas, the formulas are multiplied by -1 and subtracted
from the particular setpoint.
In auto operation, the corrected setpoint is equal to the Time Program setpoint
minus the result of the auto formula. Mathematically:
Corrected setpoint = Setpoint hour - (8*(TW-7.39)+12) for TW > 4.25V
In manual operation, the corrected setpoint is equal to the constant setpoint minus
the result of the day formula. Mathematically:
Corrected setpoint = 20 - (8*(TW-3.99)+12) for TW < 4.25V
The DIF statements subtract the day and auto results from the appropriate
setpoints.
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