MDC Manual 1109KB - Red Lion Controls
MDC Manual 1109KB - Red Lion Controls
MDC Manual 1109KB - Red Lion Controls
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THEORY OF OPERATION<br />
In Master Mode, the <strong>MDC</strong> uses actual motor speed (Feedback Input) and an<br />
analog control voltage (Drive Output) to precisely control the motor’s speed.<br />
The <strong>MDC</strong> operates on a 10 msec control cycle. Actual motor speed is read and<br />
drive output is corrected every 10 msec. The Drive Output voltage is<br />
generated by a 12 bit DAC (digital to analog converter). Motor speed is<br />
controlled by adjusting the Output Value (in bits) to the DAC.<br />
The Output Value (0 to 4095 bits) is made up of two parts, the Open Loop<br />
term, and the correction term or Trim Value. The Open Loop term is the ratio<br />
of the Reference Speed to Maximum Speed multiplied by 4095. This is the<br />
uncorrected “Feed Forward” part of the Output Value. The Reference Speed<br />
is the current Speed setpoint taking into account any acceleration or<br />
deceleration which may be in progress. The Maximum Speed is Max RPM<br />
Feedback which is set when scaling the unit. (See the Program Scaling section<br />
of the manual for more information.)<br />
The correction term or Trim Value is derived from actual motor speed<br />
(Feedback Input) and the Reference Speed. The Trim Value is added to the<br />
Open Loop term when the <strong>MDC</strong> is running Closed Loop to provide precise<br />
control. The Error Gain determines the rate at which the Trim Value changes<br />
in response to a motor loading or a sudden speed change. The Trim Value is<br />
updated every 10 msec. It may be viewed as one of the programmable display<br />
options (see Program Displays Menu).<br />
The Drive Output voltage is then the ratio of Output Value (in bits) to 4095<br />
multiplied by the Full Scale Reference voltage. The internal Full Scale<br />
Reference is factory calibrated to 10 VDC but may be adjusted to any value<br />
within a5to15VDCrange. An external reference option also exists. (See<br />
Isolated Drive Output section of manual for more information.)<br />
In Follower Mode, the basic operation is the same except that the<br />
Reference Speed is generated as a ratio to the Lead Input speed. Also, the<br />
<strong>MDC</strong> operates on a 20 msec control cycle in order to process both Lead and<br />
Feedback input frequencies.<br />
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