Lenze MCH Series User Manual

Page 73

13435744_EDBMH01_v13

FEEDBACK @ MAX

This parameter should be set to the value of the process variable that corresponds to

the maximum transducer feedback signal (10 VDC or 20 mA).
Example:

A 0-100 psi transducer outputs 4 mA at 0 psi and 20 mA at 100 psi. Set

FEEDBACK @ MIN to 0.0 PSI and set FEEDBACK @ MAX to 100.0 PSI

(this assumes that Parameter 31 - UNITS is set to pid: PSI, and Parameter

33 - UNITS DECIMAL is set to XXX.X).

NOTE:

If a reverse-acting feedback device is being used, FEEDBACK @ MIN

should be set to the maximum process variable value, and FEEDBACK @

MAX should be set to the minimum process variable value.

PROPOR. GAIN (PROPORTIONAL GAIN)

The Proportional Gain setting represents the speed command output (in % of maximum

speed) that results from each 1% of error (1% of Parameter 75 - FEEDBACK @ MIN or

76 - FEEDBACK @ MAX, whichever is larger).
Example: If PROPOR. GAIN is programmed for 5%, and the error (difference

between setpoint and feedback) is 10%, the speed command output of the

Proportional term is 50% (10 x 5 = 50) of maximum speed.

INTEGRAL GAIN

The Integral Gain setting represents the ramp rate of the speed command output (in %

of maximum speed per second) that results from each 1% of error.
Example:

If INTEGRAL GAIN is programmed for 0.5 seconds, and the error is 5%,

the rate of rise of the speed command output from the Integral term is 2.5%

(0.5 x 5 = 2.5) of maximum speed per second.

DIFF. GAIN (DIFFERENTIAL GAIN)

The Differential Gain setting represents the speed command output (in % of maximum

speed) that results from each 1% per second change in the error.
Example:

If DIFF. GAIN is programmed for 5 seconds, and the error is increasing at

2% per second, the speed command output of the Differential term is 10%

(5 x 2 = 10) of maximum speed.

NOTE:

Differential gain is used as a “shock-absorber” to dampen overshoots in

fast-acting systems. However, it can be very sensitive to “noise” on the

feedback signal and to digitizing errors, so it must be used with caution.

PID ACCEL (PID ACCEL/DECEL)

This parameter sets the acceleration and deceleration rate of the setpoint reference into

the PID unit. When the setpoint changes, this function will “filter” the input to the PID

unit by ramping the setpoint reference from the previous value to the new value. This

will help prevent overshoots that can occur when the PID control attempts to respond

to step changes in setpoint, resulting in smoother operation. If PID ACCEL is set to 0.0

seconds, it is effectively disabled.