16
3.8
Double the bandwidth calculated in section 3.6, and then adjust the Proportional Bandwidth Potentiometer
to this new value. Fully counterclockwise = 0.5 °C, and fully clockwise = 5 °C. Each full turn of the
Proportional Bandwidth Potentiometer corresponds to 0.18 °C increment. If doubling the bandwidth yields
a value greater than 5 °C, set the bandwidth to 5 °C.
3.9
Calculate the inverse, or reciprocal, of the natural period recorded in section 3.7, and adjust the controller
Integral Rate (the number of repeats per minute) to this value. Each full turn of the Integral Rate
Potentiometer corresponds to 0.102 repeats per minute increment.
3.10
These Proportional and Integral settings are approximate settings and may need further minor adjustments.
Record the final number of turns used on the Proportional Bandwidth Potentiometer and Integral Rate
Potentiometer.
Final number of turns on the Proportional Bandwidth Potentiometer =__________________ from
maximum clockwise.
Final number of turns on the Integral Rate Potentiometer =__________________ from maximum
counterclockwise.
Additional systems with the same thermodynamic properties will operate using the Potentiometer settings
listed above.
Tuning Example
:
A.
Suppose that 16 counterclockwise turns of the Proportional Bandwidth Potentiometer (R2) were
required to just sustain a temperature oscillation. This corresponds to a proportional bandwidth of
about (5 °C
–
0.18 °C/turn x 16 turns =) 2.1 °C. (Reference section 3.6)
B.
It was then observed that the natural period of this oscillation was 2 minutes. (Reference section 3.7)
C.
The Proportional Bandwidth Potentiometer (R2) should be adjusted to double the bandwidth to 4.2 °C.
(Reference section 3.8) This is about 20.5 turns clockwise from the full counterclockwise position (0.5
°C + 0.18 °C/turn x 20.5 turns = 4.2 °C).
D.
The Integral Rate variable should be set to the inverse of the natural period by adjusting the Integral
Rate Potentiometer (R8). This is 1/(2 min) = 0.5 repeats per minute. Since each turn of the
potentiometer equals 0.102 repeats per minute, the potentiometer should be adjusted 4.9 turns
clockwise from the full counterclockwise position. (Reference section 3.9)
