Yokogawa PC-Based MX100 - Manual (Page 55)

2-41
IM MX180-01E
Integrat
on Mon
tor
3
2
1
4
5
App
Index
Notes on Computaton
• The equation is not case sensitive. The exception is tag numbers specified on the
Channel setup screen.
• The precision and range of computed values are the same as data in single-precision
floating point format.
• The sampling interval of the computed channel is 100 ms to 10 min.
• Measured value used in computations
The measured value with the closest time is used among the measured values
existing at the time of computation. Resampling of the measured value or interpolation
are not performed while computation is being executed.
Example 1:
If the measured values indicated by and exist and computation indicated by
is performed, the measured value indicated by on each channel is used. If the
measured value does not exist such as in Ch 5, NaN is used as the measured value.
Ch 1 : : Data at time t
Ch 2 : : Data near time t
Ch 3 : : NaN
Ch 4 : : Oldest data
Ch 5 : : NaN
Computation :
t Measured value used in
the computation of
Example 2:
If the disconnection (disconnected after ) is detected, NaN is used as the measured
value of Ch 3.
Ch 1 : : Data at time t
Ch 2 : : Data near time t
Ch 3 : : NaN
Ch 4 : : Oldest data
Ch 5 : : NaN
Computation :
t
Measured value used in
the computation of
• Alarm values used in computations
Basically handled the same as measured values except the behavior differs in the
following two cases.
• When the alarm value does not exist (Ch 5 in example 1 above)
Always returns 0 (no alarm).
• When the communication is cut off (Ch 3 in example 2 above)
Always returns the most-recent value.
• Syntax error and execution error
• Syntax error
Equations containing items that are inappropriate are indicated in peach when the
equation is being entered. If monitoring is started without correcting the equation,
they are ignored.
• Execution error
Execution errors are detected after starting the execution. Below are the two cases.
NaN is returned as the result in either case.
• When the reference destination does not exist when monitoring is started
• When the computed result is undefined.
• Handling of NaN values
• In the case of a TLOG function (tlogmax, tlogmin, tlogpp, tlogsum, and tlogave)
If NaN exists in the channel values, it is handled as though the value did not exist.
• In the case of the IsNan() function
This function can determine whether the value is NaN.
• NaN is ignored for the functions min, max, sum, ave, and pp.
2.5 Settng Computatons (Settng the Computaton Channels)