User guide

P/N: 021-00154, Rev. A.6 - updated for V4.7 Tools Page | 154
always get there before the system does. Proportional control alone is the simplest to use, but will result in some
steady state error. Increasing the proportional term enough to limit the steady state error to a small value can
cause over shoot and oscillation. The integral term adds up the error as a function of time and drives the output
harder as the error increases and as time in error increases. An analogy is that the integral of the flow rate of
water is the depth in a bucket. The integral error term is positive when filling the bucket and will go negative
when the bucket is filled beyond the desired level. The integral term is typically slower to respond (i.e. correct an
error), but will cause an extremely small final error as any detectable error will continue to add up till the output
changes in direction to correct it. This term can also cause oscillation if set too high, and will need the help of
the P term for fast machine operation. The differential term reacts to the speed of change in the detected error.
This term is primarily used to slow down the change in system output as it nears the correct state, to limit over
shoot. DVC products do not implement this term in our valve controllers, as we do not believe they will benefit
from it.
DVC products provide selectable PID tuning options for each valve in your system. You can vary the P and I
values or use our defaults. Experience with your particular valves will indicate whether our defaults, you’re
changing of the defaults or even writing you won PID loop is best for your systems performance
See HCT manuals for more details on how to tune our products.