DeVilbiss DeVO/MC44-90 - Alarm System; Patient Alert System; Microcomputer Control Board

SECTION 5
ALARM SYSTEM
Most problems encountered with the DeVO/
MC44 are indicated by the patient alert system.
This system is comprised of both visible and
audible alarms which alert the patient when
there is a malfunction. Further isolation of
problems are indicated by alarm lights located on
the MC board. These are designed to help service
personnel troubleshoot problems within the unit.
The alarm system is monitored and activated by
the MC board.
A. Patient Alert System
1. Visible Alarm System - The visible alarm
located on the control panel says “Service
Required” (2 Fig. 2). When this panel is
illuminated it indicates a unit malfunction
such as low pressure, valve, sieve bed, or
compressor failure. A severe restriction of
flow will also cause this panel to
illuminate. A more definitive description
of the type of problem can be found by
observing the alarm indicator lights on
the MC board.
NOTE: The “Service Required” panel will
come on momentarily when the unit is
turned on. If it stays on for an extended
period, or comes on while the unit is
operating, refer to the troubleshooting
guide in Section 6.
2. Audible Alarm System - The audible alarm
will sound when there is a low or high
pressure, power, valve, or other
component failure that activates the
alarm system. This alarm will sound when
the unit is turned on until the
accumulator has had time to pressurize. It
is
powered by a 9 volt alkaline battery.
The alarm itself is located on the backside
of the MC board. When activated the
alarm transmits the sound through the
control panel (3 Fig. 2).
B. Microcomputer Control Board
The microcomputer contro! board or MC
board (7 Fig. 12) is located on the inside front
cover of the unit. It is responsible for
monitoring and controlling the entire system
as well as the alarms by using a pressure
transducer (13 Fig. 12).
When the pressure sensed by this transducer
indicates a malfunction, the alarm system will
be activated whether it is for a pressure or
component failure. Alarms will also be
activated if the system fails to operate within
10/87
the pre-set minimum and maximum cycle
times.
The DeVO/MC44 is designed so its alarm
system cannot be overridden. For example, a
disconnected or weak battery will not prevent
the patient from being alerted to a system
malfunction because the visible alarm system
is still operational. Also, most major
malfunctions will cause the unit to shut off
automatically, thus preventing any further
damage to the unit.
The MC board has four red indicator lights (8
Fig. 12) labeled short cycle, long cycle, no
cycle and high pressure. These lights indicate
what type of malfunction has occurred in the
unit. They should be used as a trouble-
shooting aid in conjunction with the
information that can be derived by attaching
pressure test gauges to the test points (Fig.
22) on the manifold. Refer to normal! cycling
sequence on page 24.
When a malfunction occurs these alarm
indicator lights will come on in a certain
sequence. One or possibly two lights will
illuminate when the unit shuts off. In all
cases, whether one or two lights come on,
further testing must be done to determine
the exact cause of the problem since there
may be more than one possible cause for a
malfunction. An explanation of each alarm
light is given below along with possible
causes for the malfunction.
1. Short Cycle: This light indicates the sieve
beds have pressurized too soon. A
minimum and maximum cycle time has
been pre-set on the MC board. If the sieve
beds pressurize so quickly that the
minimum cycle time is reached, this alarm
will be activated.
Possible Cause: Severe bed contami-
nation will cause a decreased cycle time
and activate this alarm. A failure of the
four-way valve or a severe restriction of
flow may also cause this alarm to come
on.
NOTE: The short and no cycle lights will
come On together whether it is a bed or
four-way failure. Further testing must be
done to determine the exact cause of the
problem. Refer to Service Instructions,
Section 7 for the proper testing proce-
dures for the sieve beds and four-way.