MA7200 PLUS Operating Manual
TECO – Westinghouse Motor Company App-1 PID Control
APP-1
PID Application Note
The PID control (loop) serves to maintain a given process within certain limits whether it be, pressure, flow etc. To do this
a feedback signal representing the actual process value is compared to a set-point, the desired process value, and the
difference becomes the error signal for the PID control. The PID control then responds by trying to minimize this error.
How small the difference becomes is dependent upon the value of the
Proportional Gain
set by parameter Bn-17(P-gain).
The greater the gain, the lower the difference becomes. However, in any system as the gain is increased there is a point
that the system may become unstable (oscillate). To correct this instability, the response time of the system can be
adjusted by using parameter Bn-18 (
Integral Time
) to slow the response and / or Bn-17 (
Derivative Time)
to increase the
response. However slowing the system down too much may be unsatisfactory for the process and too high a response
can result in instability. The end result is that these parameters in conjunction with parameters Bn-01 (acceleration) and
Bn-02 (deceleration) times are adjusted to achieve optimum performance for a particular application.
The MA7200 PLUS supports two independent PID loops; a Main PID control and an External PID control. The main PID
control is used for a process that is controlled by the motor. The external PID control may be used to regulate an external
function such as temperature, using the inverter output terminal AO1 or AO2. Both PID loops can be used simultaneously
but there are certain parameters that are common to both that must be assigned to one or the other. This is covered in
detail later in this application note.
1.0 Main PID Control
1.1 PID Parameters
The following tables, 1.1.1 and 1.1.2 below show the various parameters used in the PID function.
Table 1.1.1 PID Parameters
Function
Parameter
No.
Name and
Description
LCD display
(English)
Setting range
Setting
Unit
Factory
Setting
Setting
of PID
Control
Parameter
Bn-16
PID Detection Gain
Bn-16= 01.00
PID Cmd. Gain
0.01-10.00 0.01 1
Bn-17
PID Proportional
Gain
Bn-17= 01.00
PID P_gain
0.01-10.00 0.01 1
Bn-18
PID integral time
Bn-18= 10.00s
PID I_Time
0.00 -100.00s
0.01s
10.00s
Bn-19 PID
Differential
Time
Bn-19= 0.00s
PID D_Time
0 -1.00s
0.01s
0.00s
Bn-20 PID
Bias
Bn-20= 0%
PID Bias
0 -109%
1%
0%
Cn-55
PID Integral Upper
Bound
Cn-55= 100%
PID I-Upper
0 -109%
1%
100%
Cn-56
PID Primary Delay
Time Constant
Cn-56= 0.0s
PID Filter
0.0 - 2.5s
0.1s
0.0s
Cn-64
PID Target Upper
Limit
Cn-64 = 100%
PID Target U_Limit
0 - 100%
1%
100%
Cn-65
PID Target Lower
Limit
Cn-65 = 0%
PID Target L_Limit
0 - 100%
1%
0%
Cont.
