P
AGE
39
A Position Proportioning sensitivity adjustment is provided, which specifies a deadband
around the setpoint to prevent the valve from oscillating. The valve rotation time must be
entered, for proper operation, into the Tune mode paramter Ct1.
See Figure 4-1 for proportional bandwidth effect on the output.
FIGURE 4-1
Proportional Bandwidth Effect On Output
Process
Variable
100%
0%
Output
Action
Setpoint
PB=100
100%
0%
Output
Action
PB=50
100
200
Setpoint
125
175
150
150
The Proportional Bandwidth is the area where the output is a percentage of the full output. The
size of the proportional band determines what change in the output will result from a change in the
process variable. In the upper figure when the process variable is at 125 the output will be at 75%
of full output. In the lower figure the proportional bandwidth is smaller. When the process variable
is at 125 the output is now at 100%. The larger the proportional band the smaller the "gain" and
vice versa.
