PCU12005 datasheet(67/96 Pages) REDLION

67 / 96 page

PID CONTROL

PROPORTIONAL BAND

Proportional band is defined as the “band” of units the process changes to

cause the percent output power to change from 0% to 100%. The band may or

may not be centered about the setpoint value depending upon the steady state

requirements of the process. The band is shifted by manual offset or integral

action (automatic reset) to maintain zero error. Proportional band is

expressed as percent of scaled display range.

The proportional band should be set to obtain the best response to a

disturbance while minimizing overshoot. Low proportional band settings (high

gain) result in quick controller response at expense of stability and increased

overshoot. Settings that are excessively low produce continuous oscillations at

setpoint. High proportional band settings (low gain) result in a sluggish

response with long periods of process “droop”. A proportional band of 0.0%

forces the controller into ON/OFF control mode with its characteristic cycling

at setpoint (See

ON/OFF Control, page 62, for more information).

INTEGRAL TIME

Integral time is defined as the time, in seconds, in which the output due to

integral action alone equals the output due to proportional action with a

constant process error. As long as a constant error exists, integral action

repeats the proportional action every integral time. Integral action shifts the

center point position of the proportional band to eliminate error in the steady

state. The units of integral time are seconds per repeat.

Integral action (also known as “automatic reset”) changes the output power

to bring the process to setpoint. Integral times that are too fast (small times)

do not allow the process to respond to the new output value. This causes over

compensation and leads to an unstable process with excessive overshoot.

Integral times that are too slow (large times) cause a slow response to steady

state errors. Integral action may be disabled by setting the time to zero. If time

is set to zero, the previous integral output power value is maintained.

If integral action is disabled, manual reset is available by modifying the

output power offset (“OPOF” initially set to zero) to eliminate steady state

errors. This parameter appears in unprotected parameter mode when integral

time is set to zero. The controller has this feature to prevent integral action

when operating outside the proportional band. This prevents “reset wind-up”.

-59-

Figure 28, Proportional Band

Figure 29, Integral Time

Note: The Proportional band shift due to integral action may itself be

“reset” by temporarily setting the controller into the ON/OFF control

mode (proportional band=0)

PCU12005 Datasheet(PDF) 67 Page - Red Lion Controls. Inc

PCU12005 Datasheet(HTML) 67 Page - Red Lion Controls. Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96

Datasheet Download

Link URL