Despatch MIC1462 Controller Manual - Manual (Page 28)

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3.3 On-Off Control
On-Off control can be implemented with SPDT relay or SSR driver output(s) by setting
the corresponding proportional band (Pb) to 0.0. On-Off operation can be assigned to
Output 1 only (Output 2 not present), Output 1 AND Output 2, or Output 2 only (Output
1 is time proportional or current proportional). A hysteresis adjustment is provided for
On-Off outputs, "HySl " for Output 1 only, "HySt" for Output 1 AND Output 2, or "HyS2"
for Output 2 only. This adjustment is in % of input span and defines the bandwidth of
the hysteresis. Relay chatter can be eliminated by proper adjustment of this parameter.
When operating in On-Off control, the output(s) will turn on or off depending upon the
setpoint, the process value, and the hysteresis adjustment.
3.4 Time Proportioning Control
Time Proportioning control can be implemented with a SPDT relay or SSR driver. Time
proportioning control can be selected for either Output 1 or Output 1 and Output 2,
depending on hardware configuration. Time proportioning control is accomplished by
cycling the output on and off during a prescribed period of time when the process
variable is within the proportional band.
Ex:
Calculated output % = 40%; Cycle time adjustment = 32 seconds
Output on time =.4 x 32 = 12.8 seconds
Output off time = .6 x 32 = 19.2 seconds
When the unit is operating in the Control Mode, the control algorithm determines the
output % required to correct for any difference between the process value and the
setpoint. The output calculation is affected by Tune Mode parameter adjustments. See
Figure 3-1 for proportional bandwidth effect on the output.
3.5 Current Proportioning Control
Current Proportioning control can be implemented on units provided with mADC current
output(s). Current Proportioning control provides a 4 to 20 mADC or 0-20 mADC output
in response to process value and setpoint. As with Time proportioning, the calculated
output % for Current proportioning is affected by the Tune Mode parameter
adjustments.
See Figure 3-1 (below) for proportional bandwidth effect on the output.