Toshiba G7 Series Applications Workbook page 12

Tuning the PID
The idea when tuning this PID is to get fast enough response from the drive that the pressure doesn't drop or increase very much. One
problem with this is that if the response is too quick, the drive can actually overshoot (put out a higher frequency than necessary), and
in extreme cases, oscillations can occur. The object then when tuning a PID loop is to minimize the rise and settling times.
40
Hz
30
The above figure illustrates what is meant by the rise and settling times. Suppose that a G7 is running at 30 Hz. At Time 0, all of the
valves in the example system open. Suppose also that the drive now needs to speed up to 40 Hz to maintain the desired pressure. The
rise time, is the time it takes to go from Time 0 (pressure change) to the needed Hz (for the first time). As seen in the above graph,
there can be some oscillations that (hopefully) settle out after a time called the Settling Time. Remember that as the output frequency
changes, so does the pressure. THE USER MUST DECIDE WHAT ARE ACCEPTABLE RISE AND SETTLING TIMES.
The rise time, settling time, and overshoot are dependent on the system and can be adjusted by changing three of the parameters in the
table programming above: Proportional Gain, Integral Time, and Differential Time.
Some recommended PID values based on application type:
Process Variable
Flow
Levels: fast
Levels: slow
Pressure: fast
Pressure: slow
Temperature: fast
Temperature: slow
Temperature: furnace
Compressor speed
For additional assistance, please contact Toshiba Adjustable Speed Drive Marketing Dept. at (800) 872-2192
efesotomasyon.com -Toshiba inverter,drive,servo,plc
PID Drive Output Hz vs. Time
(in response to pressure drop)
Settling
Rise Time
Ti
Time 0
Proportional Gain
0.3
1.0
0.25
2.0
1.0
1.0
1.0
0.8
1.0
Time
Integral Gain
(seconds/repeat)
0.6
8.0
16.0
0.5
2.0
2.0
16.0
8.0
2.0
Differential Gain
(seconds)
0.0
0.0
0.0
0.0
0.0
0.0
0.25
0.125
0.0
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