Fridgewatch 2100 Controller Mk4
Section 3
Publication 3-58
Issue 1.1 : 01/08
Page 115 of 152
NOTE: the value assigned to S91 Hold Low Limit must
normally be higher than the S92 Unload Low Limit.
If a Trip Limit on P1 is required but limiting is not, set S91 to a value that
will never be attained in practice.
S92 P1 (temperature) limiting: unload low limit (units: °C)
With S90 enabled, S92 defines the temperature limit below which the
Fridgewatch 2100 Controller sends unload pulses (as defined by S90)
until the value displayed by P1 does not exceed this limit; this overrides
the output from the PID algorithm or external load/unload signals.
NOTE: the value assigned to S92 Unload Low Limit must
normally be lower than the S91 Hold Low Limit.
If a Trip Limit on P1 is required but limiting is not, set S92 to a value that
will never be attained in practice.
S93 P1 (temperature) trip: trip low limit (units: °C)
With S90 enabled, S93 defines the low temperature limit at which the
Fridgewatch 2100 Controller stops the plant and displays a trip: event
code E12 Low P1 (Temperature).
NOTE: the value assigned to S93 Trip Low Limit must
normally be lower than the S92 Unload Low Limit.
If limiting on P1 is required but trips are not, set S93 to a value that will
never be attained in practice.
Configuration Settings S94 to S97: Limiting and Trips on P2 (3MIO1 Card
Analogue Input 2, Pressure Channel)
NOTE: S94, S95, S96 and S97 may be used to provide
Low Limits only, i.e. when the measured value fall below
a chosen value, for example, limiting on compressor
suction pressure.
S94 P2 (pressure) limiting/trip: unused/defined
S94 setting defines whether analogue input 2 on the 3MIO1 card is to be
used for low pressure limiting and/or trip:
S94 = 0: no limiting or trip is applied to this channel
S94 = +
x
: reserved,
DO NOT
use.
S94 = -
x
: low limit limiting and/or trips are applied to this channel
on a system wide basis not a per compressor basis.
Limiting and trip on P2 is different from limiting/trip on P4, P5 (motor
current) and the digital inputs for limiting in that they are
system
limiting
rather than
individual compressor
limiting. This is because P2 is normally
used for a common control pressure, for example, system pressure in a
common suction header.
P2 limits apply in all operating modes and:
•
If no compressors are running - Fridgewatch 2100 will inhibit
starting and Limiting appears on the front panel display for all
compressors;
•
If one or more compressors are running - Fridgewatch 2100
will HOLD or UNLOAD as appropriate and Limiting appears
on the front panel display for all compressors;
•
If two or more compressors are running when UNLOAD
limiting is in progress, S9 Next Compressor Stop Delay is
disabled so a lag compressor will stop immediately;