Cam Shaping; Cam Characteristics - ABB AV1 Operating Instructions Manual

CAM SHAPING

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 shown 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-6).
100
90
80
70
60
% OF
50
SIGNAL
40
30
20
10
0
0 10
Figure C-6. Cam Characteristics
4. Compare the curve plotted in Step 3 with the cam curves
shown in Figures C-1, C-2
(in 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 the positioner zero and span as outlined
under Zero Adjustment
make the control signal pressure versus piston (or valve) charac-
teristic conform better to the curve plotted in Step 3.
6. If the required characteristic cannot be obtained using this pro-
cedure, or if more exact characteristics are required, alter the
shape of a standard A, B or C cam or cut a new cam from a blank
cam as outlined under CAM
To assist in the alteration process, a graph is imprinted on each
cam. This graph consists of radial lines and concentric arcs. The
first and last radial lines mark the angles at which zero and 100
percent of cam rotation occurs for control purposes; the radial
CAM CHARACTERIZATION
C-6 from a cylinder or actuator that
20 30 40 50 60 70
% OF PISTON OR VALVE TRAVEL
and C-3. Select a standard cam shape
and Span Adjustment
SHAPING.
80 90 100
T00796A
in Section 4 to
CAM SHAPING
C - 5