5.
Instrumentation and Control
5.1 Operation Control System The load limiting control operates in two phases;
The Hitachi Centrifugal Chiller adopts as standard entire automatic operation system based on
one is to stop the vane opening action (limits opening
the micro computer incorporated in the console panel.
action only to stop the vane operation), and the other is to force vane closing action.
(a) Startup operation (d) Automatic start and stop
Pressing the start switch on the console panel
The signal detecting the chilled water outlet
first starts the oil pump. About 20 seconds after the oil pressure has increased, the main contactor is
temperature is processed in the micro computer to
activated and the main motor is started via the
activate the automatic start and stop switch. If the
reduced voltage starter. Once, after a certain period, it
load is lowered below the range of capacity control,
is switched to full voltage setting with the main motor in
the automatic start and stop switch stops the chiller
full-speed operation, the inlet guide vane (hereinafter
temporarily. After 15 minutes has passed and the load
referred to as the vane) is automatically started to
is recovered, the chiller is automatically restarted.
open via the temperature regulator circuit and the load (e) Failiure stop
limiter circuit without being over loaded. Then the
In case the safety switch is activated, the chiller
Chiller gets into routine operation to keep the chilled
stops operation with alarming beep while the cause of
water outlet temperature at a certain level.
the failure is indicated on the console panel. (b) Stop operation (f) Oil heater
Pressing the stop switch on the console panel
To prevent foaming of oil at startup, the oil
stops the operation of the Chiller, after the minimum vane openings, with the vane automatically closed completely. The oil
heater is automatically activated while the chiller is out
pump also automatically stops after about 4 minutes.
of operation so that the oil is kept at an appropriate temperature. (In order to do so, electric source for control system will be activated even when the chiller is off.)
(c) Automatic temperature regulator (with load limiting function)
(g) Emergency stop
The temperature regulator provides stable
Pressing the Emergency stop switch on the console
temperature control and load limiting control by applying the load limiting function to the entire circuit
panel stops the operation of the Chiller with the vane
and by adopting circuits unique to Hitachi such as
automatically closed completely. The oil pump also
integration and differential control functions.
automatically stops after about 4 minutes.
41