Appendix C - Cam Characterization; Introduction - ABB AV3 Instruction Manual

INTRODUCTION

CAM CHARACTERIZATION

APPENDIX C - CAM CHARACTERIZATION

This section provides cam shaping information. Cam shaping is the
process of changing the shape of the cam by cutting or forming so the
control signal produces the desired control characteristic. The stan-
dard cam normally does not require shaping.
Selecting or shaping these cams allows you to obtain a piston (or
valve) position versus control signal characteristic that will produce a
desired controlled medium versus control signal characteristic. An
example is a desired flow rate of air, water, or steam through a valve
for each control signal pressure applied to the positioner.
The control characteristics for which the cams are shaped are listed
in Table 3-1 and are shown in Figures C-1, C-2, and C-3. The figures
show a family of curves for each cam whose boundaries are estab-
lished by a span adjustment. Table
of specific Type AV3 positioners which corresponds to the signal span
percent values in Figures C-1,
relationship between input current to output for the servo
assembly.
1 00
90
80
70
60
S C AL E = % O F
50
S IG N A L R A N G E
40
30
20
10
0
0
1 00
Figure C-1. Cam A, Square Root Relationship
C-1 lists control signal pressures
C-2 and C-3. Table
LIM IT E D
TR AV E L
LIM IT E D
S IG N A L
1 0 2 0 3 0 4 0 5 0 6 0
S O LID L IN E IN D IC ATE S FO RW A R D TR AV EL
9 0 8 0 7 0 6 0 5 0 4 0
DA SH E D L IN E IN D IC AT ES R E VE R S E TR AV E L
S C A LE = % T R AV E L
C-1 shows the
7 0 8 0 9 0 10 0
3 0 2 0 1 0 0
T 00 79 1 A
INTRODUCTION
C - 1