Thermo King 098916, Руководство по обслуживанию

Страница: 106 / 196

105
Operating Theory
Chill Loads: (Setpoint at -9.9 C
[14.1 F] and Above)
The unit operates on Cool with Modulation and
Heat to provide accurate control of chill loads.
During Cool with Modulation, the controller uses
a proportional-integral derivative (PID)
algorithm, and a Digital Control valve to provide
accurate control of the container temperature in
direct response to load demand.
The Digital Control valve engages and disengages
the compressor to control capacity. The valve
opens and closes in response to a controller
voltage signal based on a control temperature
differential. The controller uses the setpoint
temperature, supply air sensor temperature (left
and/or right hand sensors) and pull-down rate for
the last 10 seconds, last 20 seconds and last 180
seconds to calculate the control temperature
differential.
Supply Air Sensor Control
Temperature control accuracy and protection
against frost damage is provided by using two
separate sensors (left hand and right hand) to
determine the supply temperature used to
calculate the control temperature differential:
• At setpoints below -1 C (30 F), the controller
uses the lowest supply air sensor temperature.
• At setpoints above 0 C (32 F), the controller
uses the average temperature of the left hand
and right hand supply air sensors.
• At setpoints between -1 C and 0 C (30 F and
32 F), the controller uses a sliding temperature
scale from the lowest supply air sensor
temperature to the average temperature of the
left hand and right hand supply air sensors.
If one supply air sensor fails, the controller uses
the temperature of the other supply air sensor for
temperature control. If both supply air sensors
fail, the controller uses the temperature of the
return air sensor plus an offset for temperature
control.
Frozen Loads: (Setpoint at -10 C
[14 F] and Below)
The unit operates on Full Cool and Null to
provide accurate control of frozen cargo. The
controller uses the return air sensor temperature
and setpoint temperature to regulate unit
operation.
If the return air sensor becomes disconnected or
fails, the controller uses the supply air sensors
plus an offset for temperature control.
Cooling Capacity Display in Data Menu
The percent displayed in the Data menu indicates
the cool capacity that is currently provided. For
example, when controller display shows 70
percent, this means the Digital Control valve is
operating to reduce system cooling capacity from
100 percent to 70 percent (a 30 percent reduction).
Power Limit Management
Power Limit is active whenever the compressor is
on in both the Chill and Frozen modes. When the
total current draw or the condenser temperature
exceeds a predetermined threshold, the controller
limits unit power consumption by sending a
voltage pulse to the Digital Control valve. The
Digital Control valve then operates to control the
compressor. This reduces the cooling capacity
load on the compressor, thereby limiting the
compressor motor current draw and the condenser
temperature to a predetermined threshold.
Additional power limit management flexibility is
available. A maximum total current draw (17, 15
or 13 amps) and power management time interval
can be selected from the Power Management
feature of the Commands menu. When the power
management time interval expires, the unit returns
to the standard power limit control algorithm.
NOTE: Setting power management current at 13
amps can be used to provide slow pull-down of
loads.
Compressor Vapor Injection
During compressor operation, a vapor injection
system injects refrigerant into the center scroll of
the compressor to provide additional cooling
capacity. When vapor injection is active, the