Micromod MOD: Modcell 2050R Users Guide - Manual (Page 201)

IB-23C650
DUAL OUTPUT CONTROL
DUAL OUTPUT (HEAT/COOL) CONTROL
DESCRIPTION
The controller can provide dual output (heat/cool) control with each of the
three available output types; dual dc current, dual SPDT relay, or dc current
and SPDT relay. When the controller is set up for dual control, manual tuning
is required. An option board is required when using heat/cool with dual curent
output.
Implementation of Heat/Cool control is accomplished by dividing the 0 to
100% calculated output into two parts; a heating band and a cooling band.
Activation of the heat or cool output is dependent upon the controller output
calculation and a user configured crossover point. On one side of the
crossover point the heat output is manipulated, and on the other side the cool
output is manipulated. This is illustrated in Figure 27 for reverse control
action. Heat action follows the control action of the calculated output, while
cool action is the opposite (unless the output is reversed). Note that while one
output is being manipulated (above 0% heat or 0% cool) the other output will
always be at 0% (displayed value). Both heat and cool outputs are at 0%
when within the crossover output off hysteresis set in the TUNE MENU. This
value can be set at up to ±25.0 from the crossover output value.
When Heat/Cool control is being set up, two sets of response values must be
tuned; one for heating and one for cooling. Gain and Integral (reset)
adjustments are provided for each band (heat and cool). Therefore, a transfer
from one set of tuning constants to the other must be made when the
controller output changes between the heat and cool bands at the crossover
point. The rate of change between heat gain and cool gain can be established
by configuring an adjustable crossover band width (hysteresis) in percent of
calculated output. The transition of the gain value will be linear within this
band, and the rate of change will depend on the width of the band as shown in
Figure 28. The reset transition is a step change at the crossover point. There
is a single derivative (rate) adjustment common to both the heat and cool
bands.
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