Fridgewatch 2100 Controller Mk4
Publication 3-58
Section 3
Page 112 of 152
Issue 1.1 : 01/08
A non-zero value ‘turns on’ both Limiting AND Trip functions, if only one
of these functions is required, the unwanted function must effectively be
disabled by entering a value in settings S87 and S88 or S89 that will
never be attained.
Note that as for motor current P5, there is a P4 input for each compressor
connected to Fridgewatch 2100. Limiting/trip provided by P4 is always
applied to a single compressor rather than system wide. i.e. it behaves
exactly analogous to motor current in that the state of the measured
variable monitored by this analogue input is affected only by the
associated compressor and starting another compressor will tend, in
time, to alleviate the condition.
Note also that if limiting/trip is enabled and an E48 Input Error is present
because of an over or under current being applied to this channel which
would otherwise provide limiting and/or trips, unless the package unit is in
‘manual’ start/stop - ‘manual’ capacity control mode Fridgewatch 2100
will trip the compressor. In ‘manual’ mode limiting or trips are normally
applied, but when an E48 error is present, it is the responsibility of the
user to provide another means of measuring the condition and ensuring
that the loading state does not cause damage to the equipment or
process.
S87 P4 limiting: hold limit (units: as defined by S84/S85)
With S86 enabled, S87 defines the temperature or pressure limit beyond
which compressor loading is inhibited; this overrides the output from the
PID algorithm or external load/unload signals.
Limiting appears on the front panel display when limiting is taking place.
Further load requests while limiting begin the sequence to start the next
compressor.
NOTE: the value assigned to S86 Hold Limit must
normally be within the S87 Unload Limit.
If a Trip Limit on P4 is required but limiting is not, set S87 to a value that
will never be attained in practice.
S88 P4 limiting: unload limit (units: as defined by S84/S85)
With S86 enabled, S88 defines the temperature or pressure limit beyond
which the Fridgewatch 2100 sends unload pulses (as defined by S86)
until the value displayed by P4 does not exceed this limit; this overrides
the output from the PID algorithm or external load/unload signals.
NOTE: the value assigned to S88 Unload Limit must
normally be outside the S87 Hold Limit.
If a Trip Limit on P4 is required but unload limiting is not, set S88 to a
value that will never be attained in practice.
S89 P4 trip: trip limit (units: as defined by S84/S85)
With S86 enabled, S89 defines the temperature or pressure limit at which
the Fridgewatch 2100 stops the plant and displays a trip: event code E14
High or Low P4 (Pressure or Temperature). The Home Page indicates
which compressor has tripped.
NOTE: the value assigned to S88 Trip Limit must
normally be outside S87 Forced Unload.
If Limiting on P6 is required but trips are not, set S89 to a value that will
never be attained in practice.
