Manual

8
Introduction
Controller Modes Description: Auto-Changeover Mode
1.5.2 Auto-Changeover Mode
In auto-changeover mode, as illustrated in Figure 1-3, the Model 286
monitors and controls liquid level measured via Channel 1, and uses liquid
supplied from two storage vessels. The A and B setpoints for Channel 1
function as the liquid level control band for the controlled dewar. The dual
AC outputs control a fill valve for each of the two storage vessels. Channel
2 is unavailable in the auto-changeover mode.
The instrument either monitors dry contacts to determine availability of
liquid from each of the two storage vessels or determines availability by fill
timeouts. The Model 286 automatically switches from one storage vessel to
the next. This allows one of the two storage vessels to be replaced when
empty without interrupting the availability of liquid to the controlled
dewar.
Storage Vessel #1
Controlled
Dewar
Fill Valve #1
Model 286
Storage Vessel #2
Fill Valve #2
Figure 1-3. Auto-changeover mode diagram illustrating the two
storage vessels and one controlled dewar.