Manually Tuning The Series 29M Control; Definition Of Input Command; Definition Of Feedback; Definition Of Error - Baldor 29M Installation And Operating Manual

Section 6

Manually Tuning the Series 29M Control

Explanation of Closed Loop Block Diagrams
Input Command
(Desired Value)
Definition of Input Command (Desired value)

Definition of Feedback

Definition of Error

MN1230
Control systems are usually represented by a series of interconnected blocks. The
blocks represent the individual functions of the system. The blocks are interconnected by
a series of lines, which represent the variable or quantity involved with directional arrows
showing the direction of information flow. See Figure 6-1.
Figure 6-1
Block Diagram of a Closed Loop System
Summing Junction
(error detector)
Error
2
Signal
S
Output
e
Any closed loop system can be divided into four basic operations:
1. Measurement of the controlled variable. The controlled variable can be
velocity, torque, etc. This measuring means is accomplished using a sensor
that converts the variable to an electrical signal that is compatible with the
control inputs, usually voltage or current. This signal now represents the
controlled variable (Feedback).
2. Determination of the error. The summing junction compares the measured
value of the controlled variable (Feedback Input) with the Input Command
(desired value) and generates a error signal. The operation is a simple
mathematical subtraction operation as follows:
Error Signal ( e ) = Input Command - Feedback
3. The error signal is then used by the control to change the motor speed or
torque.
4. The motor speed or torque is then used to reduce the error signal by driving the
control, and the final controlled variable, so that the actual value of the
controlled variable approaches the Input Command value or desired value. It
should be noted that closed loop control systems are error actuated. In other
words, an error must be present before the system will try to correct for it.
The Input Command is the input signal set by the operator. This can represent speed or
torque level.
Feedback is the signal which represents the actual measured value from the controlled
variable. This can represent a pressure, flow, speed, torque, level or temperature sensor.
This input is usually a sensor voltage or current representing the measured value.
Error is the result of subtracting the Input Command and Feedback signals.
Error is mathematically defined as:
Error Signal (
Power Input
3
Control
Feedback
1
Measuring
Means
e
) = Input Command - Feedback
Manually Tuning the Series 29M Control 6-1
Load Disturbance
4
Controlled
Variable
Motor
Controlled Variable