Hollis Prism 2 User manual

NO LIMIT
user Manual
REV.5

i |
WARNINGS, CAUTIONS, AND NOTES
Pay attention to the following symbols when they appear throughout this docu-
ment. They denote important information and tips.
This is the operations manual for the
HOLLIS PRISM 2
This manual, specifications and features of the PRISM 2 are proprietary
and copyright Hollis Inc., 2012.
This document cannot be copied or distributed without the prior
agreement and authorization from Hollis Inc.
All information contained is subject to change. Contact the
manufacturer for the latest information. www.hollisgear.com
The PRISM 2 is manufactured in the USA by Hollis Inc.,
2002 Davis Street, San Leandro, CA 94577. USA
Ph [phone]
EC Type approved by SGS UK Ltd. Weston-super-Mare. BS22 6WA.
Notified Body No. 0120.
Testing conducted by ANSTI Test Systems. Hants.
To ensure your user information is up to date. Please check
www.hollisgear.com for updates to this manual.
WARNINGS: are indicators of important information that if ig-
nored may lead to injury or death.
CAUTIONS:
indicate information that will help you avoid product
damage, faulty assembly, or unsafe conditions.
NOTES:
indicate tips and advice.

| ii
WARNING:
USE OF THE PRISM 2 MANUAL
This user manual does not, nor is it intended to con-
tain any information needed to safely dive with any type
of SCUBA apparatus. It is designed as a guide for the
proper setup, operation, maintenance, and field service
of the Hollis PRISM 2 CCR only. It does NOT take the
place of a recognized training agency instructor-led
diver-training course or its associated training manual(s)
and materials. This user manual is intended to be used
only as a type specific addition to such training and
materials, and as a user reference. This manual cannot
be used as a substitute guide for any other type of Self
Contained Underwater Breathing Apparatus (SCUBA).
PRISM 2 DESIGN TEAM
Bob Hollis
Chauncey Chapman
Art Ferguson
Robert Landreth
Matthew Addison
Peter Readey
PRISM 2 MANUAL
WRITTEN BY
Matthew Addison
EDITORS
Jeffrey Bozanic
Chauncey Chapman
John Conway
Gerard Newman
CONTRIBUTORS
Jeffrey Bozanic
Gerard Newman
Dr. Richard Pyle
Sharon Readey
Kevin Watts
Hollis PRISM 2 eCCR
User Manual
Document Control Number: 12-4072
Rev. 5
Publish Date: 5/15/2013

iii |
WARNING:
GENERAL SAFETY
No person should breathe from, or attempt to operate in any way, a Hollis PRISM 2 rebreather,
or any component part thereof, without first completing an appropriate Hollis Certified user-
training course.
Further, no PRISM 2 diver should use a Hollis PRISM 2 without direct Hollis instructor supervision
until they have mastered the proper set-up and operation of the Hollis PRISM 2 rebreather. This
includes new PRISM 2 divers as well as PRISM 2 certified divers who have been away from diving for
an extended period of time and would benefit from an instructor-led refresher course to regain skills
mastery of the Hollis PRISM 2. Failure to do so can lead to serious injury or death.
The PRISM 2 rebreather can, as with any closed circuit breathing loop, circulate breathing gas that
may not contain a sufficient quantity of oxygen to support human life. The breathing gas within the
Hollis PRISM 2 loop must be closely monitored and manually maintained with a safe oxygen content
by you (a properly trained and alert user) at all times.
The PRISM 2 computer-controlled addition of oxygen to the breathing loop is intended as a fail-
safe back-up system to you, the primary controller. If you (either knowingly or by inattention) allow
the PRISM 2 computer to control oxygen addition to the breathing loop at any time, you are diving
outside the principals of your PRISM 2 training - assuming any and all possible risk.
WARNING:
HIGH PRESSURE OXYGEN
The PRISM 2 uses cylinders, gas feed lines, pressure gauges and other devices which will
contain pure oxygen at high pressure when in operation. Oxygen by itself is non-flammable,
however it supports combustion. It is highly oxidizing and will react vigorously with combustible
materials. Oxygen at elevated pressure will enhance a fire or explosion and generate a large
amount of energy in a short time.
The user must maintain all parts of the PRISM 2 that can come into contact with high-pressure
oxygen as oxygen-clean components. This includes scheduled servicing by a Hollis service
professional, and using approved oxygen-compatible lubricants on any part of the gas delivery
systems that will come into contact with high-pressure oxygen.
If any part of the oxygen-clean system comes into contact with contaminants or is accidentally
flooded with any substance (including fresh water), you MUST have the entire high-pressure oxygen
system serviced by an authorized PRISM 2 service professional prior to use. Failure to do so can
cause fire or explosion and lead to serious injury or death.
GENERAL SAFETY
STATEMENTS + WARNINGS

| iv
WARNING:
DESIGN AND TESTING
The Hollis PRISM 2 has been designed and tested, both in materials and function to operate safely
and consistently under a wide range of diving environments. You must not alter, add, remove, or
re-shape any functional item of the Hollis PRISM 2. Additionally, NEVER substitute any part of the
Hollis PRISM 2 with third-party items which have not been tested and approved by Hollis for use
with the PRISM 2.
This includes, but is not limited to, hoses, breathing assemblies, electronics, breathing gas delivery
assemblies and their constituent parts, sealing rings, valves and their constituent parts and sealing
surfaces, latches, buoyancy devices, inflation and deflation mechanisms and on-board alternate
breathing devices.
Altering, adding, removing, re-shaping or substituting any part of the Hollis PRISM 2 with non-
approved parts can adversely alter the breathing, gas delivery or CO2absorption characteristics of
the Hollis PRISM 2 and may create a very unpredictable and dangerous breathing device, possibly
leading to serious injury or death.
Non-approved alterations to functional parts of the PRISM 2 will automatically void all factory war-
ranties, and no repairs or service work will be performed by any Hollis service professional until the
altered PRISM 2 unit is brought back into factory specifications by a Hollis service professional at
the owner’s expense.
WARNING:
COMPUTER / CONTROLLER-SPECIFIC WARNINGS
This computer is capable of calculating deco stop requirements. These calculations are predictions
of physiological decompression requirements. Dives requiring staged decompression are
substantially more risky than dives that stay well within no-stop limits.
Diving with rebreathers and/or diving mixed gases and/or performing staged decompression
dives and/or diving in overhead environments greatly increases the risks associated with
scuba diving.
WARNING:
CAUSTIC MATERIAL
The CO2absorbent used in the scrubber is caustic alkaline material. Take steps to protect yourself
from direct lung and skin contact. Furthermore, poor management of the breathing loop could
lead to water contact with the CO2absorbent, causing a “caustic cocktail” (very caustic liquid).
This could lead to severe chemical burns and if inhaled - possible drowning. Proper handling
procedures, pre-dive checks, dive techniques, and maintenance mitigates this risk.

v |
WARNING:
COMPUTER SOFTWARE
Never risk your life on only one source of information. Use a second computer or tables. If
you choose to make riskier dives, obtain the proper training and work up to them slowly to gain
experience. Always have a plan on how to handle failures. Automatic systems are no substitute
for knowledge and training. No technology will keep you alive. Knowledge, skill, and practiced
procedures are your best defense.
WARNING:
USER-PACKED RADIAL SCRUBBER
As of this writing, the Hollis PRISM 2 design does not include any technology or other device which
can detect or warn of potentially dangerous levels of carbon dioxide (CO2) within the breathing loop.
The Hollis PRISM 2 utilizes a user-packed, radial design CO2scrubber. Only Hollis tested and
approved CO2absorbents should be used, and factory-stated maximum scrubber durations
must NEVER be exceeded. Exceeding factory stated scrubber durations for a tested material will
eventually lead to serious injury or death.
It is entirely possible that, for any number of reasons including but not limited to: channeling,
ambient temperature, exhausted, damaged, inappropriately stored, or (for whatever reason), inert
scrubber material, the chemical and thermodynamic reaction required to sequester gaseous CO2
will not occur as expected, and a toxic, and possibly fatal level of gaseous CO2
within the breathing
loop can result.
You must carefully follow all instructor and manufacturer recommendations for use and handling
of CO2absorbent, never use a CO2absorbent if you cannot verify that it is able to sustain CO2
absorption and carefully pack the radial scrubber and complete a system pre-breathe prior to each
immersion, as you were taught in your training course.
Further, you must carefully monitor yourself for any symptoms of possible CO2poisoning whenever
you are breathing from the Hollis PRISM 2, and bail-out to open circuit should any physical or mental
symptom lead you to suspect elevated CO2levels in your breathing loop. Failure to bailout at the first
sign of trouble can lead to serious injury or death.

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WARNING:
WEIGHTING OF THE HOLLIS PRISM 2
Unlike open circuit scuba gear, it is possible for the Hollis PRISM 2 breathing loop to flood, causing
the rebreather to quickly become 17 pounds negatively buoyant (not including any user-added
weight or offsetting buoyancy inflation). It is the responsibility of the diver to insure that the Hollis
PRISM 2 is never weighted in such a way that it is not possible for the installed buoyancy device
to overcome the flooded weight of the unit plus any diver-added non-detachable weights, and still
provide enough positive buoyancy at the surface to keep the divers head well above water.
Consult your instructor, dealer, or call the Hollis factory directly with any questions or concerns.
Failure to maintain positive buoyancy at the surface with the Hollis PRISM 2 in a fully flooded state
can lead to serious injury or death.
WARNING:
PROPER BATTERIES
ONLY name-brand batteries (such as “Duracell” or “Eveready”) may be used to power the PRISM
2. Off-brand / Discount batteries have been found to vary greatly in quality of materials from batch
to batch (and even piece to piece!) Therefore they may not perform as expected, or be capable of
consistently delivering the power required to drive the components, despite battery voltage levels
reported by a battery voltage meter.
While off-brand / discount batteries are perfectly acceptable for use in toys and flashlights,
they have no place in life support gear and must never be used to power any component of
your PRISM 2.
Because of the potential rapid drop-off of charge from rechargeable batteries, rechargeable
batteries are not recommended for use with your PRISM 2 rebreather and must not be used.
Diagram showing rapid discharge of non-branded batteries,
which in life support gear can result in unnecessary hazards.
The full article, “Are Expensive Batteries Worth The Extra
Cost?” is available at Wired.com
Image courtesy of Rhett Allain, Wired

vii |
TABLE OF CONTENTS
General Safety Statements & Warnings
PART 1
SYSTEM OVERVIEW
SECTION 1
DESIGN PHILOSOPHY
Manual Control or Computer Control
SECTION 2
GETTING TO KNOW
YOUR PRISM 2
Schematics + Design
ARTICLE: TAKING CARE OF YOUR
OXYGEN SENSORS
ARTICLE: THE SOLENOID AND
THE PID CONTROLLER
SECTION 3
FITTING YOUR PRISM 2
ARTICLE: STABILITY
PART 2
SETTING UP YOUR PRISM 2
eCCR
SECTION 1
AN O-RING CLEANING PRIMER
SECTION 2
PACKING THE PRISM 2 CO2
SCRUBBER
SECTION 3
SETTING UP YOUR PRISM 2
USING CHECKLISTS
SECTION 4
PRISM 2 COMPONENT INSPECTION
SECTION 5
PRISM 2 ASSEMBLY ORDER
SECTION 6
PRISM 2 OPERATIONAL CHECKLIST
SECTION 7
POST DIVE CHECKLIST
SECTION 8
PRISM 2 eCCR MAINTENANCE /
REPAIR LOG SHEET
iii-vi PART 3
IN WATER SKILLS
SECTION 1
PRISM 2 IN-WATER SKILLS + DRILLS
ARTICLE: MINIMUM, MAXIMUM AND
OPTIMAL LOOP VOLUMES AND WORK
OF BREATHING
SECTION 2
SKILLS + DRILLS COMPLETION LIST
PART 4
MAINTENANCE +
CLEANING
SECTION 1
SERVICE FACILITY & YOU
SECTION 2
ROUTINE CLEANING
PART 5
APPROVED PRODUCTS,
CAPACITIES, & SPECS
SECTION 1
THE LANGUAGE OF OXYGEN
SECTION 2
LIST OF APPROVED PRODUCTS FOR USE
IN YOUR PRISM 2 REBREATHER
SECTION 3
COMPONENT CAPACITIES + SPECS
SECTION 4
GLOSSARY OF TERMS
TABLE OF CONTENTS

| 2
PART 1 . Section 1
MANUAL CONTROL OR COMPUTER CONTROL?
One of the ongoing debates when discussing rebreather safety is whether manually controlled
or electronically controlled rebreathers are safer. From the day in 1995 when PRISM Topaz class
#1 was held in Hermosa Beach, CA, students were taught to “fly” their rebreathers manually by
watching their secondary analog displays and manually injecting oxygen and diluent as needed.
From day one, PRISM students were taught that the primary control system was always the divers
brain. It wasn’t until the last dive of the last day of class that students were told, “OK, you can turn
on your electronics and experience a computer controlled dive”.
Diving with the computer monitoring the oxygen and the user keeping an eye on everything with
(at that time) a Heads Up Display primary and a wrist-mounted analog secondary sure kept us
busy, but we quickly realized that the computer was a LOT better at closely maintaining a set
point! We also realized that our instructor had trained us to be manually controlled rebreather
divers with the safety of “computer over-watch”.
Why two independent monitoring systems in one rebreather? Simply put, electronics, batteries
and wiring combined with salt water (or even fresh water) do not get along well together. While
we can seal circuit boards and wiring interfaces against water intrusion, rebreathers should have
a diver accessible compartment to change batteries, and because of this need for accessibility,
flooding can occur.
This is the Achilles heel of rebreathers with on-board electronics. Any time an O-ring sealed
Compartment is unsealed, the potential for debris to get on the O-ring and cause the
compartment to flood during the next dive is increased.
So, with two separate systems onboard with separate battery compartments, if one battery
compartment floods and destroys the battery, we simply switch to the other monitoring system to
safely end the dive. When our dive is over, we dispose of the wiring harness and battery, clean the
compartment and put in a fresh battery and new O-ring(s).
// DESIGN PHILOSOPHY
The PRISM family of rebreathers has a long and illustrious history, and it is
considered one of the foundation platforms of the modern day electronically
controlled “sport” rebreather.
The PRISM 2, like its forerunner the PRISM Topaz, is a digitally controlled
electronic closed circuit rebreather with split front-mounted over the shoulder
counterlungs (OTS-CL). It incorporates a radial design scrubber for the best
possible duration and work-of-breathing. All gas delivery systems on the PRISM 2
have both automatic and manual function.

3 |
GETTING TO KNOW
YOUR PRISM 2
SCHEMATICS + DESIGN
THE GAS PATH
The PRISM 2 incorporates an over-the-shoulder split counterlung design.
The gas flows through the loop from left to right shoulder as has become
a standard in the recreational rebreather market (Fig. 1.1).
Fig. 1.1

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PART 1 . Section 2
OXYGEN AND THE EXHALATION SIDE
OF THE LOOP
Pure oxygen injection into the system, whether manually or electronically,
via the solenoid, is injected into the exhalation side of the breathing
loop. This design insures that a diver can never inadvertently get a high
PO2dose of oxygen while diving, and that oxygen has plenty of time to
properly mix with the loop gas and thereby avoid potentially dangerous
O2spikes.
HEAD PLATE + RED CO2SEAL
Once the diver-exhaled gas enters the head, it travels into the head plate,
which is also where O2injected by the solenoid enters the breathing
loop. The red CO2seal (Fig. 1.2) which seals the scrubber basket to
the head plate sits in a groove at the end of the head plate facing the
scrubber basket. The Red CO2seal must be in place at all times during
diving operations! Failure to insure that the Red CO2seal is properly
installed may lead to injury or death.
THE SCRUBBER BASKET
The gas leaves the head plate and enters the radial scrubber basket
through its center tube (Fig. 1.3). As the gas radiates outwards through
the CO2absorbent and towards the bucket walls, exhaled CO2is
chemically sequestered (adsorbed) by the CO2absorbent, and any added
oxygen is mixed with the loop gas as it travels through the scrubber
granules. Upon exiting the scrubber, the heated gas enters the thermal air
jacket area between the basket and bucket.
The air jacket serves two purposes: First and most important, it insulates
the scrubber material from colder external temperatures, which helps
increase the efficiency of the absorption process. Secondly, the moisture
in the heated gas exiting the scrubber has an opportunity to condense
along the cooler bucket wall, dropping the overall humidity of the gas
entering the oxygen sensor housing.
WARNING: Breathing from the PRISM 2 without the Red
CO2Seal in place will result in 100% gas bypass of the
scrubber.
Fig. 1.2
Fig. 1.3

5 |
From the thermal jacket, the gas flows up through the scrubber basket
flow vanes (Fig. 1.4). This restriction creates higher gas velocities in the
sensor area without increasing work of breathing, further dropping the
dew point of the gas as it reaches the oxygen sensors. By using natural
condensation along the surface of the bucket wall and manipulating gas
velocities in the area around the O2sensors, we are able to keep the
sensors as dry as possible without adding complexities such as sponges
or other moisture blocking devices.
THE INHALATION COUNTERLUNG
The inhalation counterlung is a 3.5 L (optional 2.5 L) front-mounted split
counterlung design (Fig. 1.5) made of rugged nylon with a food-grade
urethane interior. It houses the automatic diluent addition valve (ADV),
counterlung drain, hose mounting hardware and BCD inflation hose wrap
at its front.
The hose attaching hardware for both the head and DSV/BOV assembly
attaching points (Fig. 1.6) are welded into place, so they cannot become
loose and cause an unintended loop flood. The DSV/BOV hose attaching
hardware is “keyed” (Fig. 1.7) and will only accept the corresponding
hose assembly elbow, thereby avoiding incorrect assembly of the loop
which would result in potential reversal of gas flow within the loop.
Behind each counterlung, under the Fastex Buckle panel are weight
pockets (Fig. 1.8) which will accept up to 5 lbs/2.3 kg of hard or soft
weight. The weight pouch flap is held in place with Velcro. There are 2
D-rings on the counterlung, one on the side and one at the bottom. Each
counterlung has a water drain at its bottom (Fig. 1.9) to drain fluids as
they accumulate during a dive. The Fastex clip panel on the back of the
counterlung contains 2 Fastex clips for clipping the counterlungs to the
harness, backplate, and one chest strap with Fastex clips.
Fig. 1.4
Fig. 1.5
Fig. 1.6
Fig. 1.7
Fig. 1.8
Fig. 1.9

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PART 1 . Section 2
ADV (AUTOMATIC/MANUAL DILUENT ADDITION VALVE)
Having the ADV (Fig. 1.10) on the inhalation side of the loop makes sense
for several reasons. Should the oxygen content ever become dangerously
low, dangerously high, or the diver begins feeling “abnormal”, a known
normoxic gas is immediately available while still breathing from the loop
prior to switching to bailout*. Therefore, having the diluent as close to the
mouthpiece as possible is the best way to insure that fresh breathing gas
of known and safe oxygen content is only a breath away.
*(Not applicable if the diluent is a hypoxic mix)
The ADV is held in place by a threaded fitting welded to the counterlung.
To remove the valve for servicing, unscrew the outside retaining nut by
turning it counter-clockwise until the valve comes loose. There is a rubber
gasket under the valve which seals the valve body to the counterlung
fitting. The removable plunger activates a Schrader valve which allows the
gas to flow into the loop. The counterlung fitting is keyed so the valve will
not rotate while in use. While the valve is shipped from the factory with the
QD fitting facing up, the valve will work in any rotation.
THE EXHALATION SIDE COUNTERLUNG
The Exhalation side counterlung is of similar build and size to the
Inhalation side counterlung in all respects excepting it houses the manual
oxygen addition valve and the automatic, adjustable loop over-pressure
valve (OPV). (Fig. 1.11)
BREATHING HOSES + HARDWARE
The Breathing hoses (Fig. 1.12) are 15” X 11/2” fixed-length rubber
breathing hoses. They can not be cut to a different length. The
Inhalation hose hardware which connects the hose to the DSV/BOV and
counterlungs, also houses the inhalation mushroom valve on the DSV
side of the hose. The BOV inhalation hose does not house the inhalation
mushroom valve. All mounting hardware is held in place by 2 Oetiker
clamps on each side of each hose.
Fig. 1.11
Fig. 1.10
Fig. 1.12

7 |
OPV (OVER PRESSURE VALVE)
The OPV (Fig. 1.13) is an automatic or manual adjustable pressure
relief valve which is screwed into a fitting welded onto the front of the
exhalation counterlung. To adjust the release pressure of the ADV, simply
turn the body of the valve clockwise to increase the cracking pressure
and counter-clockwise to decrease cracking pressure. To operate the
valve manually, simply depress the body of the valve. The OPV is not a
serviceable part so should it ever fail, it must be replaced.
MANUAL OXYGEN ADDITION VALVE
The manual oxygen addition valve (Fig. 1.14) is located on the inside
of the exhalation counterlung. It is a push button valve operated by
a schrader valve. Under the quick disconnect fitting is a 0.0020 inch
flow restrictor, to meter the injection of oxygen into the Loop. The
manual oxygen valve is held in place by a threaded fitting welded to
the counterlung. To remove the valve for servicing, unscrew the outside
retaining nut by turning it counter-clockwise until the valve comes loose.
There is a rubber gasket under the valve which seals the valve body to the
counterlung fitting. The counterlung fitting is keyed so the valve will not
rotate while in use. While the valve is shipped from the factory with the QD
fitting facing up, the valve will work in any rotation.
DSV (DIVE SURFACE VALVE)
The Dive Surface Valve (Fig. 1.15) is a neutrally buoyant one-way loop
“shut down” valve with a water purge. The rotating barrel is made of
stainless steel. The exhalation mushroom valve is seated on the right side
of the valve housing.
BOV (BAIL-OUT VALVE)
BOV (Bail Out Valve) (Fig. 1.16) is a unique 2-position neutrally buoyant
loop shutdown valve with an in-line second stage for single action bail out
to open circuit. When the lever is in the top position, the valve in closed
circuit mode. The lower position is open circuit bail-out.
Fig. 1.13
Fig. 1.14
Fig. 1.15
Fig. 1.16

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PART 1 . Section 2
BATTERY COMPARTMENT COVER
The battery compartment cover (Fig. 1.17) is made of aluminum. The cap
utilizes two O-rings for redundant water tightness, a radial seal on the lip
of the cap and a compression seal on the top of the battery compartment
housing.
There is an automatic pressure relief valve built into the top of the
cover to vent excess pressure should the battery compartment flood.
If the pressure release valve were ever to actuate because of a battery
compartment flood or solenoid gas containment loss, the valve will open
to vent the excess pressure and close as soon as the pressure has been
released.
BATTERY COMPARTMENT
The battery compartment (Fig. 1.18) holds two sets of batteries: two
9V alkaline batteries wired in parallel which powers the solenoid, and
one SAFT 3.6 volt LiON (Lithium Ion) battery which powers the Heads
Up Display. The sealed bulkhead power connector at the bottom of
the compartment is a female molex connector. A foam insert holds the
batteries in place.
O2SENSORS, SENSOR HOLDERS, CONNECTOR + PINS
The 3 O2sensors are located in a chamber above the scrubber basket.
This insures a low condensation area and consequently drier O2sensors.
The sensors are Hollis (PRISM 2 Ver.) which have an operating range of
8.5 mV-14 mV in air and 40.6 mV-67 mV at 100% O2at 1 atm pressure.
The holders are removable to give users better access to the O2
sensors, wiring harness and connector pins (Fig. 1.19). The holders are
manufactured from a soft silicone material to help protect the O2sensors
from vibration and minor impact forces.
See “Taking Care of your Oxygen Sensors” on the next page for more
information.
Fig. 1.17
Fig. 1.18
Fig. 1.19

9 |
TAKING CARE OF YOUR
OXYGEN SENSORS
ARTICLE
The best way to care for an exotic animal is to first acquire some knowledge about it’s likes and
dislikes, and environments that will help the animal thrive. Likewise, having a working knowledge
of what is and is not good for the health of your oxygen sensors will help you take the best care
possible of them, and hopefully avoid unnecessary mid-season damage replacement. Here are
some important questions, and their answers.
WHAT IS A GALVANIC O2SENSOR?
An oxygen sensor is a very small electrochemical generator. Some people equate them to a battery,
but that comparison is largely incorrect since a battery does not produce electricity as the O2sensor
does, and the O2sensor does not store electrical energy as a battery does. Understanding that the O2
sensor is more like a delicate power-generating machine than a robust Duracell D battery is your first
clue in understanding how they should be handled.
WHAT MATERIALS ARE USED TO MANUFACTURE THE HOLLIS PRISM 2
SENSORS?
The body of the sensor is made of High-Density Polyethylene (HDPE). The membrane on the front
of the sensor is a thin Teflon gas permeable membrane. The internal components are comprised of
a lead anode, a precious metals-plated cathode, a base pH electrolyte consisting of mostly water
and a bit of Potassium Hydroxide. A printed circuit board (PCB) with resistor-thermistor temperature
compensation circuitry is heat sealed to the outside back of the sensor.
WHAT ENVIRONMENTAL CONDITIONS ARE BEST AND WORST FOR THE O2
SENSOR?
Your “PSR” series O2sensors are happiest between 32 oF/0 °C and 122 oF/50 °C. Operating or storing
the O2sensor above 122 oF/50 °C will prematurely dry out the electrolytic fluid and destroy the sensor.
Operating or storing the O2sensor below 32 oF/0 °C will freeze the electrolytic fluid causing expansion
damage to the internal components, Teflon membrane, and possibly leakage of the electrolyte upon
thawing, thereby destroying the sensor.

| 10
PART 1 . Section 2
HOW DOES CHANGES IN AMBIENT TEMPERATURE INFLUENCE THE O2
SENSOR’S PERFORMANCE?
Temperature influences the signal output at a rate of 2.54% per °C. Gradual ambient changes in
temperature can be maintained within +-2% accuracy by processing the signal output through the
resistor - thermistor temperature compensation network. Rapid changes of 59 oF/15 °C require 45-
60 minutes for the compensated signal output to equilibrate, e.g. the electronic thermistor reacts
immediately to offset the change in the sensor, but the sensing membrane and electrolyte reacts at a
much slower rate.
Because of the exothermic (heat generating) reaction of CO2scrubbing taking place next to the
sensor housing during diving operations, it is important that you calibrate the sensors close to “room
temperatures” (60 oF/16 °C – 80 oF/27 °C) so you are not temporarily outside of the 59 oF/15 °C “rapid
compensation” range while diving.
HOW DOES PRESSURE INFLUENCE THE OXYGEN SENSOR’S
PERFORMANCE?
Pressure influences the signal output on a proportional basis. The sensor is accurate at any
constant pressure up to 30 ATM provided the sensor (front and rear membranes) is pressurized and
decompressed gradually (similar to human lungs). The membranes, especially the front sensing
membrane, do not tolerate rapid changes in back pressure or vacuum. Normal diving operations will
not generate pressures beyond which the sensor is designed to operate.
If you use a pressure vessel to check current limiting, it is important that you slowly bleed off the
pressure in the vessel after the checks are completed. The optimal analysis pressure range is 5-30
psig, up to 100 PSIG, with a flow rate of 1-2 scfh. The longer you keep the cells pressurized, the slower
you need to bleed off pressure. This procedure should sound familiar to divers.
WHAT IS THE MAXIMUM ALTITUDE THE OXYGEN SENSOR CAN BE EXPOSED
AND STILL FUNCTION?
The oxygen sensors have been tested up to 20,000 ft/6096 m with no error.
DOES MOISTURE OR WATER AFFECT THE OXYGEN MEASUREMENT?
If moisture or water is present in the gas stream it will not damage the oxygen sensor or analyzer, but it
can collect on the sensor’s sensing membrane, thus blocking the flow of gas.

11 |
WHAT HAPPENS WHEN THE O2SENSOR HAS BEEN EXPOSED TO WATER?
The collection of condensation on the sensing surface of the sensor (standing water) reduces the
signal output. Once either drying or gravity removes the standing water, the signal output will return to
normal within 30 seconds. For example, a thin layer of water over the sensing surface will reduce the
signal output of a sensor from 11.8 mV to 10.1 mV within 20 minutes; remove the standing water and
the signal output returns to 11.8 mV in 30 seconds.
CAN A SENSOR BE CONTAMINATED BY CARBON DIOXIDE (C02) GAS,
REDUCING THE SENSOR LIFE?
Exposure of the sensor with its base electrolyte to carbon dioxide (CO2) gas or any other acid gas
will produce crystal-like deposits on the cathode, which reduces the surface area of the cathode and
the corresponding signal output. This effect is cumulative, cannot be reversed and can dramatically
reduce the expected sensor life. This means that attempting to “Push the Scrubber” beyond its factory-
stated duration, or breathing into a loop without active scrubber material installed could shorten the
life of your O2sensor.
CAN THE OXYGEN SENSOR BE DAMAGED IF DROPPED OR IF THE
REBREATHER IS DROPPED?
Absolutely! Sensors are fragile and can be damaged in a number of ways. Dropping a sensor by
itself or while mounted in the rebreather can result in: broken wires, broken electrical connections,
dislodging the anode. Dislodged anodes cause a broken connection or an internal short as the loose
anode comes in contact with the cathode connection. If the motion stop-force is applied onto the
sensor face, the liquid electrolyte can be forced onto the Teflon membrane, stretching the material
and destroying the sensor. Testing has shown that dropping a sensor one time from 3 ft/1 m onto a
carpeted concrete slab can result in an immediate
25-100% reduction in signal output.
Types of forces known to cause sensor damage while housed in a rebreather include but are not
limited to transportation shock (baggage handler throwing distance competitions, driving over rough
terrain, jolts during heavy seas and extreme motor vibrations). It is always recommended that you
temporarily remove the sensors from the rebreather if it may be subject to any of the above conditions.
WARNING: Salt water can corrode or bridge electrical con-


| 12
PART 1 . Section 2
CAN I TOUCH THE TEFLON MEMBRANE WITH MY FINGER? HOW DO I CLEAN
THE SENSOR CONTACTS?
No, you must not touch the sensor face with anything, especially your fingers. Fingers have oils on
them even when freshly washed, and the oil permanently clogs the membrane, destroying the sensor.
If salt has dried on the sensor face, you can gently pour a bit of distilled water on the membrane and
allow it to air dry. Never use any cleaning solutions on the sensor face. You may use an electronics
contact cleaner such as DeoxIT®GOLD GN5 on the contact pins, but use it sparingly and wipe off all
residual cleaner before use.
WHAT IS THE EXPECTED OXYGEN SENSOR LIFE?
The operational life of the Hollis (PRISM 2) sensors are calculated as one year from the date they are
put in service. There is a “DO NOT USE AFTER” (date) also. Whichever date comes first is the proper
time to discontinue sensor use. DO NOT attempt to extend the life of the sensors. Doing so can result
in incorrect, erratic, or no signal output which can lead to serious injury or death.
WHAT IS THE RECOMMENDED STORAGE TEMPERATURE?
During a “diving season” (if one exists for you) the oxygen sensors, when stored, should be kept
in a cool, ambient, unsealed environment to insure they are immediately operational. If you will be
storing the sensors for a month or more, you can place them in an airtight container in a refrigerated
environment that is kept above 34 °F/0.1 °C to insure that the electrolyte does not freeze (see
“Environmental Conditions”). While this will not extend the operational life of the sensor, it may reduce
response time degradation during the latter part of its 12-month service life.
After storage, you will need to acclimate the sensors by placing them in air at room temperature for 24
hours prior to putting the sensors back in service. Failure to acclimate the sensors after storage can
cause the sensors to read incorrectly and possibly lead to injury or death.

13 |
ARE THE O2SENSORS DATE CODED?
Oxygen sensors have a finite life. Understanding the date code is vital to getting the benefit of
the warranty period. As an example, the serial number 10734789 breaks down as follow: Digit #1
a (1) denotes the year of manufacture as 2011; digits #2, #3 (07) indicate July as the month of
manufacture; the remaining digits are sequential for uniqueness. As the result of a number of issues
related to the use of aged sensors, Analytical Industries has added a “DO NOT USE AFTER: (date)”
to the sensor’s labeling. For a sensor with less than 12 months in service, this date supersedes. If
the sensor is past the “DO NOT USE AFTER: (date)”, discontinue use of the sensor. DO NOT use it
regardless of how it seems to perform.
WARNING: You must NEVER
-

WARNING: ALWAYS acclimate sensors to ambient air for a
