Fridgewatch 2100 Controller Mk4
Publication 3-58
Section 3
Page 28 of 152
Issue 1.1 : 01/08
The method used to start the compressor depends on the control mode
selected by the operator. All possible modes are listed in Fig 8.
In manual start/stop mode, the operator supplies the start signal by
turning the Supervisor Key to the Unlocked position and pressing the
button on the Fridgewatch 2100 front panel. Having started successfully,
the compressor runs until Fridgewatch signals it to stop, initiated by the
operator pressing the STOP COMPRESSORS (ALL MODES) button,
changing the operating mode to ‘off’ or by a trip occurring. Similarly, with
remote start/stop mode selected, a remote controller supplies the start
signal. The compressor runs until the remote signal is removed, the
operating mode is changed to ‘off’ or a trip occurs.
For the remaining option, auto start/stop mode, Fridgewatch 2100 looks
for the start measured variable (pressure or temperature) to rise above
the start value before signalling the compressor to start. In a multi-
compressor application, subsequent compressors will start in the manner
described in 5.3. Basics of Starting and Stopping Compressors. When
the measured variable falls below the stop value, all compressors
currently running are stopped.
Additionally, with auto start/stop selected, it is possible to use early start
value S15 to define a rate of change required to start the compressor.
This facility can be used in circumstances where a sudden load might be
applied to the system, and waiting for the start value to be exceeded
would introduce an unacceptable delay before the compressor starts.
Using this method, the Fridgewatch 2100 monitors the chosen input and
if it sees a rate of increase which exceeds early start value S15, it will
start the compressor regardless of whether the actual start value is less
than that normally required to start.
In manual and auto start/stop mode, compressor operation can be made
subject to an external run enable signal by changing the setting of S14
Run Enable Signal Required; refer to the description of S14 in 11.1.
Operator Settings. Fridgewatch 2100 cannot start the compressor until
the external run enable signal is available, even though the start
measured variable or early start value S15 are requesting a start.
Removing the external run enable signal stops the compressor, including
any slave compressors in a master/slave configuration, and prevents
restarting until the signal is restored.
As an example of using the run enable signal, Fridgewatch 2100 controls
compressor capacity on suction pressure using a pressure transducer
input while a thermostat signals when refrigeration is required via run
enable signal S14.
5.7. Compressor
Running
Order
Operator setting S42 determines the number of the first compressor
controlled by FW2100. This is usually set to 1 so that the first
compressor on the plant is compressor 1, second compressor 2 and so
on. However, when two or more package units are linked together
through a Compressor Master Station, alternative inputs are possible.
To avoid confusion, throughout these instructions, when a multi-
compressor application is referred to, the first compressor will always be
called compressor 1, the second compressor 2 and so on.
Having established the compressor numbering designations, the running
order can be set using operator setting S4 to tell Fridgewatch 2100 which
is the lead compressor.
