Honeywell EXCEL 5000 User Manual page 275

EXCEL CARE CONTROL ICONS
Switching Table Example
Gray Switching Table
This example shows how to set the start-up action for a two-stage ventilator. After
power returns, the ventilator should start in the first stage, even if the Time Program
that controls the ventilator requests the second stage. The following diagram shows
the switching logic required for this application:
The switching table with the gray background defines start-up action after a power
failure.
Line 2 of the switching table contains the determining condition. The controller sets
STARTUP to 1 before the application program starts. Because Line 2 contains a
switch-on delay, the table transmits the 1 only after a delay of 20 seconds. Until
then, the condition of this line, STARTUP=0, is true. After 20 seconds, the table
senses STARTUP=1 and the condition is false. The table sets STARTUP to zero.
Note that you do not use a switching table with a zero output because zero
switching tables do not automatically toggle between 1 and 0. In other words, zero
switching tables do not generate a one when they become false.
CAUTION
Delay time (Te) must be larger than the maximum cycle time. This action
guarantees that a DDC cycle is done before STARTUP switches to zero. Only
then can other switching tables evaluate the negative cycle.
Line 3 of the table provides a "self-latching" function. If STARTUP was previously
equal to 1, it sets STARTUP to 1 again. If STARTUP was previously equal to zero, it
sets STARTUP to zero again. In effect, STARTUP does not change immediately to
277
APPENDIX B: STARTUP USER ADDRESS
EN2B-0184 GE51 R0518 (Europe)
74-5577–33 (US)