48VTR English 9/00 Ver. 2.7
10
Control
Relay
Alarm
Relay
AC Power
Load
Wiring the Alarm and Control Relays in Series
8
9
4
5
6
7
Meter Contacts
Figure 4
13. RAMP AND SOAK FUNCTIONS
The Extech 48VTR controller operates as a fixed setpoint controller. However, the
controller offers several advanced features which can enhance your application. These
include Ramp-to-Setpoint and Soak/Event Timers. Refer to the details below.
13.1 Ramp-to-Setpoint (‘rAmP’ Parameter)
To limit the rate at which the controller allows the process (PV) to move towards
setpoint (SV), enter a value in units per minute for the 'rAmP' parameter. The
programmable limit ranges from 0.0 to 100.0 units per minute. The controller will
automatically adjust its outputs to observe this limit. Setting this parameter to zero
defeats the Ramp-to-Setpoint function. The “rAmP” parameter will not appear if
“Parameter Lock” (P-L) is set to a “0” or “2”.
13.2 Soak Timer Function
The Soak Timer function allows the process to ramp to setpoint and remain (Soak) at
that setpoint for a user-programmable period of time. Set the "A1Fu" parameter to
either '10' (Soak ON-TIMER) or '11' (Soak OFF-TIMER) depending upon the application
(refer to Table IV in Appendix A for the difference between ON and OFF Timers). Set
the Soak time in parameter 'timE' in the First Programming Level. The Output and
Alarm Relays must be wired in series so that the Alarm relay can switch the control
relay at the appropriate times (refer to Fig. 4). For example, when a setpoint of 500
o
F is
reached, the Soak time (programmed by the user under parameter 'timE") begins to
countdown. After the desired Soak time has elapsed, the Alarm relay switches thereby
switching the Control relay circuit.
13.3 Event Timer Function
The Alarm relay can be
programmed to switch state at
desired times in a process. This
is accomplished by first setting
the alarm function in parameter
"A1Fu" to either an EVENT-ON
or EVENT-OFF timer (refer to
the function list and Table IV in
Appendix A for the difference
between ON and OFF Timers).
Next, select a countdown time
in parameter ‘timE’. The relay
timer will start counting down
when the PV equals the SV.
For example, while maintaining a certain temperature for 4 hours, an event is to take
place 2 hours into the process. The Event, in this example, is the controller's alarm
relay activating a pump. To do this, set the alarm function to an EVENT-ON Timer
(selection 8) in parameter "A1Fu". Set the time to 120 minutes (2 hours) in parameter
"timE". When the controller is powered the alarm relay will be OFF, when the PV = SV
the relay remains OFF but the timer begins to countdown, and after 2 hours the relay
will turn ON permitting the process event to take place.
