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351579-YTS-B-0608
alarms, it will overwrite the oldest alarm after the history buffer
becomes full.
Some system errors will initiate a controlling response as well
as being stored in the error memory buffer. See the
"Troubleshooting" chapter in this manual for a detailed
description of how controller errors are handled.
Data items stored for maintenance / run history, in addition to
Alarms:
• Accumulated run times for each compressor and heat stage
• Unit model number
• Unit serial number
• Unit Name
DIGITAL LINGO
This training manual is intended to help you with the
commissioning process by illustrating the use of tools like the
control's digital input and software engineered specifically for
starting up and servicing a Millennium
You should become familiar with some common terminology
and lingo used in the digital controls industry. (If you are familiar
with the Synthesys controller, the logic of the Simplicity
familiar territory.)
If this is your first exposure to the world of digital controls you
may experience a lot of new terms, acronyms and technical
lingo commonly used in the controls industry. For example, the
®
input and output hardware points are described as
Simplicity
analog, relating to a continuous scale of value readings such
as a temperature sensor ranging from -40
binary, meaning 2-states, either on or off, open or closed, true
or false, one or zero. The term "digital" also means two states
and its use is often interchanged with "binary". These points
may be either factory- or field-set.
THE PI ALGORITHM
Another common "digital controls" term is the PI algorithm or
Proportional-Integral control loop. The PI algorithm is a
continuously updated math calculation that the controller uses
to modulate an analog output point. For example, a variable
speed drive uses a PI loop to maintain a desired setpoint (in this
case, a duct static pressure value). The algorithm takes into
account several parameters to calculate the output. The PI loop
needs parameters such as the proportional operating
bandwidth, integral time constant, deadband, desired setpoint
value, sensed input value(s), start up ramp time, initial start
value, maximum output control value, a status point to initiate
the control action (i.e. a fan ON status), Direct or Reverse
Controlling Action, and several other parameters to calculate a
simple 0 to 100% analog output control. The PI algorithm is also
called a PI loop because it "loops" the output back to the input
(feedback) and determines a new output value based on the
"error" or difference between the setpoint value and the sensed
input value, and how that difference relates proportionally to the
0 to 100% output value. Time is the "integral" constant that is
factored in to increase or decrease the controlling output action
4
®
rooftop unit.
®
will be
0
0
F to 160
F range, or
depending on how long the sensed value remains away from its
desired setpoint.
Fortunately, you do not have to determine all of these
parameters since they are pre-programmed at the factory. You
need only to set a desired setpoint and ensure that the inputs
and outputs are properly wired and working. This is referred to
as commissioning a system.
ANALOG TO DIGITAL CONVERTER
Computers can only understand a simple binary language.
Remember, "binary" means two states - ON or OFF. Analog
(continuous) values of voltages, currents, and resistances are
supplied by sensors and transducers to the control. These
values must be converted in to a binary code so that the
computer can understand them. This conversion process is
performed through a combination of hardware and software.
For example, the 0-5VDC analog value from a static pressure
transducer is divided into thousands of steps with a binary
coded number, often called "counts", assigned to each step.
0
1
2
3
4
BINARY NUMBER EQUIVALENT
Figure 3: Analog to Digital Converter
SOFTWARE TERMINOLOGY
A digital controller handles its control functions through software
programming rather than with interlocking hardware and wiring.
The software then becomes key to how controlled functions are
handled. Software is a set of statements (referred to as the
"program") that define the function of the controller's internal
microprocessor computer.
Software procedurally tells the computer the sequence and
order of tasks that need to be performed using a language that
the computer can understand.
Software is stored in a computer's memory. There are several
types of memory in a computer. Each type has a specific
function to perform.
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Johnson Controls Unitary Products
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