22
3.3 Direct/Reverse Operation of Outputs
Direct operation is typically used with cooling applications. On-Off direct output(s) will
turn on when the process variable exceeds setpoint. Proportional direct output(s) will
increase the percentage of output as the process value increases within the
proportional band.
Reverse operation is typically used with heating applications. On-Off reverse output(s)
will turn off when the process variable exceeds setpoint. Proportional reverse output(s)
will decrease the percentage of output as the process value increases within the
proportional band.
Output 2 will be Direct when Output 1 is selected as Reverse, and Reverse when
Output 1 is selected as Direct.
3.4 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 O.O. 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.
3.5 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
To Next Page
Loading...
Need help?
General
