High Country Tek DVC80 - Manual (Page 15)

P/N: 021-00154, Rev. A.6 - updated for V4.7 Tools Page | 15
First, every DVC module be it a DVC5/7/10 or DVC expansion module has an internal program or BIOS to
control the module’s operation and its communications over the CAN Bus. All of the modules operate
asynchronously with their own internal clock. The BIOS sets module internal circuits to correspond to the
input/output configurations you specify using the Programming Tool. The BIOS of a DVC expansion module
gets the input output configurations the user configured using the Programming Tool from the master
DVC5/7/10 through a series of CAN Bus messages. Once this profile is loaded into the module’s memory, the
module will setup, read and write to the inputs and outputs based on their individual type, configuration settings
and the application program.
Second, as your system operates, the DVC5/7/10 and each of the DVC expansion modules continuously
exchange messages between each other over the CAN Bus. Each expansion module sends messages
detailing the state of each of its hardware supported inputs and outputs. These messages include whether a
digital input is closed or open, an analog input’s voltage as a percentage of the user specified (i.e. configured)
voltage range and error flags such as a short being detected on a reference output pin. These messages are
received by the DVC5/7/10 and stored into its I/O memory. After receipt, the DVC controller has a complete
status of each of the expansion module’s input and output states. Similarly, the DVC5/7/10 records in I/O
Memory the state of its inputs and outputs. The application program references I/O Memory using predefined
variable names to decide what to do to control the system.
Third, in parallel with messages being transmitted between the DVC5/7/10 and other modules, the user’s
application program is being processed. As your application executes it can look at the current state of any of
the system input and output settings stored in the I/O memory. Usually it is looking for some specific input to
change (i.e. a digital input is closed or a new analog input value from a joystick movement) and as a result it will
transition to another state or bubble in the application where it will control an output in a certain way or look for
another input change.
Fourth, the DVC5/7/10 executes their resident user application and BIOS in a defined sequence, over and over,
typically in 10ms intervals. During each interval, any CAN Bus messages to be sent or that have been received
are processed. Next, it updates the input and output status for its own I/Os. Next, it analyses the Bubble logic
transition conditions for the application program. For instance, if your application is waiting on a digital input
from an expansion module to be closed to advance from its current state or bubble to the code in another
bubble that is done at this time. Finally, the Always code is executed for your application and then the active
bubble or new bubble’s code (after a transition) for the current logic sequence.
Finally, one other point worth noting for system operation is that the status of input and output pins is
communicated back and forth between modules often as a percentage of a user defined voltage or current
range. Thus a potentiometer setting can directly control a proportional value where the percentage of
movement of the potentiometer directly relates to the position of the valve. Also a nonlinear response can be
defined by using an IO Function curve to translate a potentiometer position percentage to the valve current
percentage. All of this behind the scenes BIOS processing and CAN Bus messaging makes application
development much easier than would otherwise be possible.
1.7 Closed Loop Control Principles
Closed loop control is a means whereby a feedback signal to the DVC is measured against a desired level or
set point. If the values differ then a corrective action is taken. The corrective action is generally a new valve
current setting that is obtained by adjusting up or down the PWM duty cycle. This adjustment is a continuous
process during operation and compensates for environmental factors such as high resistance wires or off spec
valves. In a PID system like that used by the DVC family the adjustment amount is a function of the error (set
point - feedback) and P and I terms. The P term scales the current adjustment proportional to the error and the
I-term scales the correction as a function of the error over time. These corrections are summed. The D term is
not used. Generally the higher the values of the P and I terms the faster the error will be corrected. Correcting