Red-lion MDC User Manual download pdf (Page 9)

THEORY OF OPERATION

In Master Mode, the MDC uses actual motor speed (Feedback Input) and an

analog control voltage (Drive Output) to precisely control the motor’s speed.

The MDC operates on a 10 msec control cycle. Actual motor speed is read and

drive output is corrected every 10 msec. The Drive Output voltage is

generated by a 12 bit DAC (digital to analog converter). Motor speed is

controlled by adjusting the Output Value (in bits) to the DAC.

The Output Value (0 to 4095 bits) is made up of two parts, the Open Loop

term, and the correction term or Trim Value. The Open Loop term is the ratio

of the Reference Speed to Maximum Speed multiplied by 4095. This is the

uncorrected “Feed Forward” part of the Output Value. The Reference Speed

is the current Speed setpoint taking into account any acceleration or

deceleration which may be in progress. The Maximum Speed is Max RPM

Feedback which is set when scaling the unit. (See the Program Scaling section

of the manual for more information.)

The correction term or Trim Value is derived from actual motor speed

(Feedback Input) and the Reference Speed. The Trim Value is added to the

Open Loop term when the MDC is running Closed Loop to provide precise

control. The Error Gain determines the rate at which the Trim Value changes

in response to a motor loading or a sudden speed change. The Trim Value is

updated every 10 msec. It may be viewed as one of the programmable display

options (see Program Displays Menu).

The Drive Output voltage is then the ratio of Output Value (in bits) to 4095

multiplied by the Full Scale Reference voltage. The internal Full Scale

Reference is factory calibrated to 10 VDC but may be adjusted to any value

withina5to15VDCrange. An external reference option also exists. (See

Isolated Drive Output section of manual for more information.)

In Follower Mode, the basic operation is the same except that the

Reference Speed is generated as a ratio to the Lead Input speed. Also, the

MDC operates on a 20 msec control cycle in order to process both Lead and

Feedback input frequencies.

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Red-lion MDC User Manual Page 9