United Process Controls PROTHERM 50, Руководство по эксплуатации

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UNITED PROCESS CONTROLS GMBH Page 21 Protherm 50 P68.230
Comparator 1..4
PT50 provides 4 independent, versatile comparators, which integrate the functionality of a limit compar-
ator and a window comparator with adjustable tolerance time.
Both compare variables may be picked from a general variable table. The comparator mode (“lim-
it/window”) specifies, whether the comparator performs a simple limit compare (“value 1 is less
than/greater than value2”) or a window compare (“value 1 is within/outside value 2 +- tolerance band”)
The diagrams below show the details:
Limit mode
At the moment when value 1 climbs above value 2, the tolerance timer starts. If the limit violation per-
sists during the entire tolerance time, the internal limit flag is raised. If, during the tolerance time, the
value 1 falls below value 2, the tolerance timer is reset and a new limit violation has again to exist for
the whole tolerance time in order to raise the limit flag.
Window mode
Around the value 2, there is a symmetrical tolerance window, which is twice the tolerance band wide.
At the moment when value 1 leaves this tolerance window, the tolerance timer starts and if value 1
stays outside the window for the entire tolerance time, the limit flag is raised. If value 1 returns to the
tolerance window within the tolerance time, the timer is reset, a new violation must again exist for the
whole tolerance time to raise the limit flag.
If the tolerance time is set to zero, any limit violation raises the limit flag immediately.
The limit flag may be used to activate a relays directly or it may be assigned to the alarm or alert sys-
tem.
In the table of comparable values, there is an entry called „fixed lim”. This refers to a variable, that may
be set to a fixed value by the user. If “fixed lim” is selected as on of the compare values, a classical limit
compare function with a fixed compare limit results.
A good example for the use of the window comparator mode is a regulator band alarm with delayed
action. Set the comparator mode to “window”, select the real value of a regulator as value 1 and the
setpoint of that regulator as value 2. Then set the tolerance band and the tolerance time to the desired
settings, assign the limit flag to the alarm system and you will have a comparator function, that raises an
alarm if the real value stays outside the tolerance band for longer than the tolerance time.
The tolerance band is expressed in the units of the compared variables.