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12 McQuay OM 751
Description of Operation
Description of Operation
State Programming
The MicroTech II UVC takes advantage of “state” machine programming to define and
control unit ventilator operation. “State” defines specific states or modes of operation for each
process within the unit ventilator (e.g., heating, cooling, etc.) and contain the specific logic for
each state. This eliminates some of the most common problems associated with control
sequences such as the possibility of simultaneous heating and cooling, rapid cycling, etc.
State machine programming, and the unique nature of state diagrams, can be easily used to
describe operation. It can simplify sequence verification during unit commissioning, as well as
simplify troubleshooting. With the unique combination of state machine programming and the
keypad/display’s ability to allow a technician to easily determine the active UVC state,
troubleshooting the UVC can be very simple.
The state diagrams presented in the following sections consist of several “elements” including
super states, states, conditional jumps (also called transitions) and transition points. Super
states are used as a means to group two or more related states into a single control function
such as cooling, or heating, etc. States are where all the actual work takes place, within each
state the UVC enables PI-loops and other logic sequences required to control unit ventilator
operation within that particular state, while other functions and PI-loops not needed during
that state may be disabled. Conditional jumps, or transitions, are the logic paths used by the
UVC to determine which state should be made active, these are the “questions” the UVC
continually considers. The transition point is simply a point through which a number of
conditional jumps meet. Think of it as a point where a number of questions must be
considered from which the UVC then determines which path is followed and which state is
then made active.
The UVC states and super states are used to define the “normal” unit modes, such as Off,
Night Purge, Fan Only, Emergency Heat, Auto, Cool, and Heat. The UVC also supports
several “special purpose” unit modes such as Purge, Pressurize, De-pressurize, and Shutdown,
which can be forced via a network connection and override typical UVC operation.
Note – Not all states or modes are available for all UV configurations, and some states (such as
Active Dehum) are optional.
– In the state descriptions below the terms, saturated high and saturated low, indicate that
the heating or cooling function being described has reached 100% or 0%, respectively.