High Country Tek emc-3L - Manual (Page 11)

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 valve 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 I/O Function curve to translate a potentiometer position percentage to the valves 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
too fast can cause over correction (i.e. overshoot) depending on the latency experienced by the feedback signal
changing given the adjustment. Most systems require the P and I terms to be tuned based on how your system
behaves.
It should be noted that when you desire a valve’s current to be set to 1 ampere for instance from 0 amperes the
PID system works as if the error at time zero is 1 ampere and the adjustment mechanism then sets the actual
PWM% to begin to correct the error. By plotting a particular PWM variable using the Program Loader Monitor’s
graph facility you can see how the correction is accomplished as a function of time for tuning purposes.
The DVC710 controller provide for 3 distinct and different closed loop control mechanisms. They are:
1. Automatic proportional valve current regulation
2. Software controlled closed loop proportional valve current based on a sensor’s feedback signal indicating
pressure, position, temperature or RPM.
3. Software only closed loop control used typically for long latency systems.
In the first case, the PID technique is employed by the DVC hardware and BIOS to set and maintain the valve
coil current to the desired value.
In the second case, your application software calculates the feedback value and the set point and the DVC
hardware and BIOS adjusts the valve current (PWM %) based on the difference between the set-point (or
target) and the calculated feedback.
In the third case, you control the PWM % setting through a
repeatedly executed piece of software that reads sensor
input and does its own form of a PID adjustment.
1.8 Programming and Debugging the DVC710
The Windows PC based DVC710 Programming Tool gives
you the ability to program the DVC modules to work in a
variety of applications without large development costs.
Some knowledge of Windows, computer programming and
electro-hydraulics is beneficial.
P/N: 021-00163, Rev. A.0 - for V5.2 Tools Page | 11
DVC Intella Programming Tool