ABB AV2123000 Positioner User Manual

CAM CHARACTERIZATION
% of
Control
Signal
Table C-1 relates the percentage of control signal to the corresponding
pressure values of the input signal. Table C-2 relates the
percentage of control signal to input (current) and output (pounds
per square inch gage) values of the I/P converter.
Table C-1. Control Signal Pressure Conversions (AV1)
Control System Spans
20.7 to 103.4 kPa
(3.0 to 15.0 psig)
20.7 to 186.2 kPa
(3.0 to 27.0 psig)
% of
Control
Signal
Control System Spans
20.7 to 103.4 kPa
(3.0 to 15.0 psig)
20.7 to 186.2 kPa
(3.0 to 27.0 psig)
kPa psig kPa psig kPa psig kPa psig
0 20.7 3.0 20.7 3.0 60 70.3 10.2 120.0 17.4
10 29.0 4.2 37.3 5.4 70 78.6 11.4 136.6 19.8
20 37.2 5.4 53.8 7.8 80 86.9 12.6 153.1 22.2
30 45.5 6.6 70.4 10.2 90 95.2 13.8 169.7 24.6
40 53.8 7.8 86.9 12.6 100 103.4 15.0 186.2 27.0
50 62.1 9.0 103.5 15.0
Table C-2. Input to Output I/P Converter Relationships (AV2)
% of
I/P Converter
% of
I/P Converter
Control Input Output Control Input Output
Signal
mA kPa psig
Signal
mA kPa psig
0 4.0 20.7 3.0 60 13.6 70.3 10.2
10 5.6 29.0 4.2 70 15.2 78.6 11.4
20 7.2 37.2 5.4 80 16.8 86.9 12.6
30 8.8 45.5 6.6 90 18.4 95.2 13.8
40 10.4 53.8 7.8 100 20.0 103.4 15.0
50 12.0 62.1 9.0
CAM SELECTION
In a system involving only a single actuator or cylinder, the B cam
is probably satisfactory and should be tried first. However, one of
the other cams may provide a more stable control over a wide
range of operation within a given proportional band gain adjustment
on the controller. Where the actuator or cylinder is part of a
complex control system, the three standard cams A, B and C provide
a choice of control characteristics. The cam, in conjunction
with a span adjustment, are likely to meet the control characteristic
required for the system.
Steps is selecting a standard cam for a particular application are:
1. With the B (linear) cam in place, determine and plot the actual
controlled medium versus piston (or valve) position characteristic
by manually adjusting valve position and measuring the controlled
medium (Fig. C-4).
CAM SELECTION
C - 3