IDEC MicroSmart - Manual (Page 362)

21: PID I NSTRUCTION
21-6 « FC4A M ICRO S MART U SER ’ S M ANUAL »
Example:
When type K thermocouple is connected, the analog input data ranges from 0 through 4095. To convert the analog input
data to actual measured temperature values, set the following parameters.
Linear conversion (S1+4): 1 (enable linear conversion)
Linear conversion maximum value (S1+5): 1300 (1300°C)
Linear conversion minimum value (S1+6): 0 (0°C)
S1+7 Proportional Gain
The proportional gain is a parameter to determine the amount of proportional action in the proportional band.
When auto tuning is used by setting the operation mode (S1+3) to 1 (AT+PID) or 2 (AT), a proportional gain is determined
automatically and does not have to be specified by the user.
When auto tuning is not used by setting the operation mode (S1+3) to 0 (PID), set a required value of 1 through 10000 to
specify a proportional gain of 0.01% through 100.00% to the data register designated by S1+7. When S1+7 stores 0, the
proportional gain is set to 0.01%. When S1+7 stores a value larger than 10000, the proportional gain is set to 100.00%.
When the proportional gain is set to a large value, the proportional band becomes small and the response becomes fast, but
overshoot and hunching will be caused. In contrast, when the proportional gain is set to a small value, overshoot and
hunching are suppressed, but response to disturbance will become slow.
While the PID action is in progress, the proportional gain value can be changed by the user.
S1+8 Integral Time
When only the proportional action is used, a certain amount of difference (offset) between the set point (S3) and the pro-
cess variable (S1+0) remains after the control target has reached a stable state. An integral action is needed to reduce the
offset to zero. The integral time is a parameter to determine the amount of integral action.
When auto tuning is used by setting the operation mode (S1+3) to 1 (AT+PID) or 2 (AT), an integral time is determined
automatically and does not have to be specified by the user.
When auto tuning is not used by setting the operation mode (S1+3) to 0 (PID), set a required value of 1 through 65535 to
specify an integral time of 0.1 sec through 6553.5 sec to the data register designated by S1+8. When S1+8 is set to 0, the
integral action is disabled.
When the integral time is too short, the integral action becomes too large, resulting in hunching of a long period. In con-
trast, when the integral time is too long, it takes a long time before the process variable (S1+0) reaches the set point (S3).
While the PID action is in progress, the integral time value can be changed by the user.
S1+9 Derivative Time
The derivative action is a function to adjust the process variable (S1+0) to the set point (S3) by increasing the manipulated
variable (D1) when the set point (S3) is changed or when the difference between the process variable (S1+0) and the set
point (S3) is increased due to disturbance. The derivative time is a parameter to determine the amount of derivative action.
When auto tuning is used by setting the operation mode (S1+3) to 1 (AT+PID) or 2 (AT), a derivative time is determined
automatically and does not have to be specified by the user.
When auto tuning is not used by setting the operation mode (S1+3) to 0 (PID), set a required value of 1 through 65535 to
specify a derivative time of 0.1 sec through 6553.5 sec to the data register designated by S1+9. When S1+9 is set to 0, the
derivative action is disabled.
Process Variable after Conversion (S1+0)
Analog Input Data
Linear Conversion Maximum Value (S1+5): 1300 (1300°C)
Linear Conversion Minimum Value (S1+6): 0 (0°C)
4095 0