West Control Solutions MRC 7000 Profiler Manual - Manual (Page 45)

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To start the profile running, press the RUN/HOLD key while in the Profile Continue mode. The
profile selected will start at the point selected.
4.1.2.4 ON-OFF CONTROL
On-Off control can only be implemented on controllers provided with SPST relay or SSR
driver output(s). On-Off operation can be assigned to either or both output 1 and 2 for each
pen. The On-Off control can be selected as direct or reverse acting. Direct action is typically
used in cooling applications. The output device will turn On when the process value is greater
than the setpoint. Reverse action is typically a heating application. The output device will turn
On if the process value is below the setpoint. A hysteresis adjustment is provided for On-Off
outputs on each pen. This adjustment is in terms of degrees/engineering units and defines
the width of the hysteresis band about the setpoint. This parameter may also be referred to
as a deadband. Relay chatter can be eliminated by proper adjustment of this parameter.
When operating in On-Off control, the control algorithm will turn the output On or Off depend-
ing upon the setpoint, the relative position of the process value, and the hysteresis adjust-
ment. The respective OUT1 or OUT2 indicator for the respective pen will illuminate to indicate
that the output device is On.
4.1.2.5 TIME PROPORTIONING CONTROL
Time Proportioning Control can be implemented on controllers provided with SPST relay or
SSR driver output(s). Time proportioning can be programed for output 1 and/or 2 for each
pen. Time proportioning control is accomplished by cycling the output On and Off when the
process value is within the proportional bandwidth selected at a prescribed time period. The
time period is selected in the Tune mode by adjusting Ct1 and/or Ct2. The On time is a
percentage of the Cycle Time.
Example: Calculated output % = 40%; Cycle Time adjustment = 20 seconds
Output On Time = .4 x 20 = 8 seconds
Output Off Time = .6 x 20 = 12 seconds
4.1.2.6 CURRENT PROPORTIONING CONTROL
Current Proportioning control provides a proportional current output in response to process
value and setpoint. The current output can be selected for direct or reverse operation. Direct
current output control is typically used for cooling applications. The current output will
increase as the process value increases within the proportional bandwidth selected. The
reverse current output control is typically used in heating applications. The current output will
decrease as the process value increases within the proportional bandwidth selected.
The instrument can be programmed to provide 0 to 20mADC or 4-20mADC current output(s).
The output selected is dependent upon the final control element being used in the process.
The output 1 and/or output 2 LED will be lighted whenever the Current Proportional outputs
are selected.
4.1.2.7 POSITION PROPORTIONING CONTROL
Position Proportioning control can be implemented on those controllers provided with two
SPST relay outputs or two SSR Driver outputs and Slidewire Feedback option for the respec-
tive pen. This control implementation can be performed on each pen.
Position proportioning control permits the use of PID control where the final control element is
a modulating device such as a motorized valve. In this form, each of the two required relays
or SSR Drivers will be used to control the valve. One output will be used to open the valve,
the other is used to close the valve. The slidewire feedback is used to provide a signal
relative to the valve armature position to the instrument.
As with the other proportioning control forms, the process input, tuning parameters and the
setpoint are used by the control algorithm to calculate the output % required to correct for the
deviation between setpoint and process.