CONTREX CX-1200 - Manual (Page 140)

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VELOCITY LOOP P1/2
The Velocity Loop screen includes parameters for the loop-type selection, the PID parameters for the
Velocity Loop (Kp, Ki, Kd), and four tuning monitor parameters
Cntrl Loop
Control Loop (MP-49) displays the present operating mode of the CX-1200. Only one type of loop can be active at a
time. These modes are automatically selected depending on the present system State (MP-50).
3 = Psn Hld (H-Stop Position Loop)
2 = Position Loop
1 = Velocity Loop
0 = Open Loop
Kp VL
Kp Velocity Loop (CP-320) is the proportional gain constant for the PID velocity loop. An increase in Kp VL (CP-320)
creates a quicker response and a smaller error. However, a value that is too large will cause instability. If the integral
term is used, (i.e., Ki VL not equal to zero) then a nonzero Kp VL can actually improve the loop response and decrease
the overshoot to some extent.
Ki VL
Ki Velocity Loop (CP-321) is the integral constant for the PID loop. Integral action provides for zero steady state error.
Increase Ki VL (CP-321) for a faster convergence to zero error. However, a value that is too large will cause instability.
Kd VL
Kd Velocity Loop (CP-322) is the derivative constant for the PID loop. Derivative action attempts to damp out
overshoot. Its effect is highly dependent on Kp VL and Ki VL, but, generally, too large a value causes instability.
FeedFwd
Feedforward (MP-35) displays the estimated voltage command to the drive required achieve the commanded RampedRef
(MP-31). It is usually the major portion of the CO Volts (MP-37) signal.
Intgrl
Integral (MP-34) displays the value of the integral term (i.e., integrated error times the Ki constant) of the PID compen-
sator. Intgrl (MP-34) is displayed in Volts. Intgrl (MP-34) is a conditioned error signal that serves to adjust the CO Volts
(MP-37) to help achieve the desired speed. It is part of the PID error correction algorithm.
Trim Out
Trim Out (MP-36) displays the value of the output of the PID compensator. Trim Out is displayed in Volts. Trim Out is
the sum of the conditioned error signals that, combined with the FeedFwd (MP-35), become the CO Volts (MP-37). Trim
Out is the combination of all three terms of the PID error correction algorithm.
CO Volts
Control Output Volts (MP-37) displays the present value, in volts, of the Control Output (CO_Sig) signal to the drive.
It is the combination of FeedFwd (MP-35) plus Trim Out (MP-36).
VelError
Velocity Error (MP-32) displays the difference between the RampedRef (MP-31) and Fb EU/Tm (MP-6).
Displayed in EU/Tm.