CAIRE Hi Flow Stroller Technical & Service Manual page 12

VI
Theory of Operation
Liquid Level Measurement
1. LED
Hi Flow Strollers are equipped with a unique liquid level meas-
urement system. This system measures the level of liquid oxygen
inside the unit with a capacitance probe and displays that liquid
level on the level meter's LEDs.
The liquid level probe consists of two concentric stainless steel
cylinders extending inside the inner vessel. As the liquid oxygen
level rises, the capacitance of this assembly goes up. The level
meter then displays the liquid level in the cylinder based on a
calibration relating capacitance to level. The higher the liquid
level in the dewar, the more LEDs are activated, beginning at the
leftmost LED.
Electrical connection between the G4 meter and the probe is
made via a single conductor JST connector. The male plug is
attached to its female counterpart extending from the probe,
creating a watertight connection. A single ground wire is con-
nected from the meter to a male spade terminal on the mount-
ing bracket.
FIGURE 4: Liquid Level Meter
Plug Connector
Probe Outer
Cylinder
Liquid Fill Tube
(Probe Inner Cylinder)
Meter Package
Male Quick
Connect Valve
The meter is powered by an internal battery, offering an esti-
mated battery life of 5 years or more at 30 actuations per day.
The meter has a low battery (LOW BATT) indicator which
signals the need for battery replacement. The meter battery is
covered under a 2-year limited warranty. If battery failure oc-
curs within 2 years of the Hi Flow Stroller shipment date, con-
tact CAIRE, Inc. customer service for a replacement meter. If the
meter battery is no longer under warranty, the CR2032 coin cell
battery can be replaced (RP2). The battery can be found at most
hardware stores, or they can be ordered through CAIRE, Inc.
customer service.
The new level meter improves upon the previous meter by in-
tegrating all components within its casing, simplifying removal
and replacement (RP8). Even more importantly from a technical
service point of view, there is a much improved calibration pro-
cedure requiring no additional tools and a range of error report-
ing codes which can be read directly from the LEDs to report
calibration errors. These calibration codes can be found in the
calibration procedure (RP5).
Hi Flow Stroller Technical Service Manual • PN 14314465 Rev F
11