MTS Series 793 - Manual (Page 357)

Mathematical errors
Arithmetic errors like divide-by-zero, or the square-root of a negative number set the resulting value to infinity,
or “Not-a-Number.” These values continue to propagate through the calculations, and will probably result in
a limit detector tripping.
Unrecoverable errors
Certain errors cannot allow the evaluation of the calculation to continue.
These errors include:
• Watch-dog time-out caused by overloading the processor
• Array index out of bounds
• Stack overflow
• Invalid number generated (NAN—not-a-number)
When one of these happens, execution of the calculation is terminated, and the signal is set to an “invalid”
state. A message is sent to the log.
If the calculated signal is used by a control mode, then this will cause an interlock. The watch-dog time-out
will cause an interlock anyway.
The result of a calculation will get clipped to the Fullscale Min/Max value.
If not-a-number occurs, the signal is set to invalid.
The user can try to recover by pressing Interlock Reset. However, if the error is not intermittent, it will just trip
again.
Calculation Parameters
About Calculation Parameters
A calculation parameter is a value used in a calculation that is not affected by the result of the calculation.
You can think of a calculation parameter as a “constant.” You define the calculation parameter value once
and that value is used wherever the parameter is used in your calculations.
Calculation parameters window
This panel defines parameters that can be used in calculated signals’ formulas. Calculation parameter values
appear in the Station Setup window’s Calculation Parameters panel.
Access
Tools menu > Calculation Editor > Calculation Editor window > navigation pane > Calculation Parameters
MTS Series 793 Control Software 357
Calculated Signals