CSZ EZT-570i, Technical Manual

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EZT-570i Technical Manual
9
4.1 Conditioning System
When the main chamber event is turned on, whether it be a standard ZP, TSB or VTS for example,
temperature control is the primary function. The air circulator/bath output will turn on and enable the
heating/cooling logic. Even though the air circulator/bath output (typically Q2 or Q44) may vary based
on the type of chamber, it performs the same function.
The minimum heat/cool enable output (Q41), if equipped, turns on with the chamber event to enable
the control circuits for heating and cooling. This output is typically only used and wired into the
control circuit when the chamber is equipped with defrost. In defrost, the output would turn off in
order to disable the heating and cooling control circuits while defrost is running.
The maximum cool output (Q1) and maximum heat output (Q31) are controlled by the configurator
settings. When the cooling or heating output percent exceeds the configurator setpoint for the on
delay period, the maximum output will turn on. They operate as boost outputs, i.e., they are on/off
outputs, not proportioning outputs. They connect additional heating and cooling circuits to the 9300
controller outputs in order to boost chamber performance.
Heating operation is relatively basic; however, the refrigeration system operation is more complicated
with staging of compressors, etc. Depending upon options present on the chamber, it may include
the rate master refrigeration system operation and/or defrost. The sequence of operation then varies
from that of a typical chamber.
4.1.1 Temperature Limited Sheath heaters
Temperature limited sheath heaters are used in applications where there is, or may be, the presence
of a flammable substance within the chamber. These heaters operate at lower surface temperatures
than standard open element, nichrome wire heaters and their surface is not electrically “live”. This
allows a temperature sensor, typically a thermocouple, to be placed on their surface. The sensor is
then connected to a limit device.
This limit device monitors the surface temperature of the heater and turns off the power to the heater
when the surface temperature exceeds the maximum operating limit. The limit device overrides any
call for heating by the chamber controller. Once the temperature drops below the operating limit,
power is restored to the heaters if heating is still required. The operating temperature limit is dictated
by the flammable material. The maximum operating temperature of the heater surface can be no
higher than 80% of the auto-ignition temperature of the flammable material in degrees centigrade.
4.1.2 Rate Master Operation
The operation of the refrigeration system varies with temperature for a rate master system. When the
chamber air temperature is above the rate master lockout setpoint, typically -20°C (-4°F), as set in the
configurator, and the air temperature setpoint is at or above the switchover setpoint, typically 0°C
(32°F), the refrigeration system operates in single stage mode. The system 1 compressor output
(Q3), solenoids output (Q30) and the rate master control output (Q40) will be on when cooling is
required.
The rate master control output is used to switch the cooling output of the 9300 loop controller from the
system 2 cooling solenoids over to the system 1 cooling solenoids. The maximum cool output will
turn on and off based on the demand for cooling as normal. The refrigeration system will switch over
to cascade mode when the air temperature drops below the switchover setpoint and the air
temperature setpoint is below the lockout setpoint. During the switch from single stage to cascade
mode, the cascade cooling control output (Q43) will turn on and the maximum cooling output (Q1) will
be disabled. This allows some of system 1’s capacity to be diverted to the cascade condenser to pre-
cool it prior to system 2 starting.