Appendix C - Cam Characterization; Introduction - ABB AV1 Operating Instructions 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 form-
ing so the control signal produces the desired control characteris-
tic. The standard 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 pro-
duce a desired controlled medium versus control signal character-
istic. 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,
figures show a family of curves for each cam whose boundaries
are established by a span adjustment.
100
90
80
70
60
SCALE = % OF
50
SIGNAL RANGE
40
30
20
10
0
0
100
Figure C-1. Cam A, Square Root Relationship
LIMITED
TRAVEL
LIMITED
SIGNAL
10 20 30 40 50 60
SOLID LINE INDICATES FORWARD TRAVEL
90 80 70 60 50 40
DASHED LINE INDICATES REVERSE TRAVEL
SCALE = % TRAVEL
C-2 and C-3. The
70 80 90 100
30 20 10 0
T00791A
INTRODUCTION
C - 1