Desired Control - ABB AV3 Instruction Manual

CAM CHARACTERIZATION
CAM SELECTION
C - 4
2. Plot the exact control medium versus control signal characteristic
given or desired for the application. This is usually a linear function
(Fig. C-5).
10 0
90
80
70
60
% O F
50
SIG N A L
40
30
20
10
0
0 1 0
Figure C-5. Desired Control
NOTES:
1. If angularity is introduced into the drive linkage, replot the con-
trolled medium versus piston travel curves. In all cases, avoid over-
stroking the final control device.
2. In terms of the Type AV4 positioner, the percent of control signal
input is related to the pulse duration; where 100 percent signal cor-
responds to the time required for full scale position change.
3. Using values determined in Steps 1 and 2, plot a curve for the
exact control signal versus piston (or valve) characteristic that will
produce the results of Figure
performs as in Figure C-4. In the examples shown, the required curve
is a mirror image of the Step 1 curve taken about the Step 2 curve
(Fig. C-7).
4. Compare the curve plotted in Step 3 with the cam curves
shown in Figures C-1, C-2
this case a C cam) whose characteristic most closely matches the
control signal versus piston (or valve) characteristic plotted in Step 3.
5. If necessary, adjust positioner zero and span as outlined under
Zero Adjustment and Span Adjustment
control signal pressure versus piston (or valve) characteristic conform
better to the curve plotted in Step 3.
2 0 3 0 40 5 0 6 0 7 0
% O F C O N TR O LLE D M ED IU M
C-7 from a cylinder or actuator which
and C-3. Select a standard cam shape (in
in Section 4 to make the
8 0 9 0 1 0 0
T 00 7 94 A