1. Preliminary Document Cochran Consulting, Inc. 31 July 2016
“Not Just Another Dive Computer”
ISO 9001:2008
FCC/CSA/EU
Certified

2. CPU Module Introduction
The Lifeguard CPU Module dive computer is a combination of a sophisticated processor, numerous sensors, a data transmitter, a Dive Data Recorder, and a Flight Data Recorder in an amazingly small package. There are a number of models with various configurations of sensors from one high pressure sensor to two high pressure sensors with up to three PO2 sensors. Certain models use negative voltage PO2 Sensors and some use positive PO2 Sensors. The Lifeguard CPU stores massive amounts of data to a very high precision at one second sampling of profiles. It stores data for 8,192 dives and over 8,000 hours of dive profiles.
It is powered by two redundant, user replaceable batteries that can provide up to two years of reliable operation. There are no rechargeable batteries to wear out, and no battery chargers to lose. Working in the background, the Lifeguard CPU automatically, unobtrusively, hands-free, measures numerous dive parameters, computes gases loadings, transmits relevant data, and provides a detailed recording of your dive data. There are no buttons, controls, or tapping. Just connect it and forget it. It even turns itself on and off automatically.
Furthermore, between dives it automatically, seamlessly is a Flight Data Recorder and records important relevant information such as altitude, temperature, and battery voltages, even while “off”.
The Lifeguard CPU Module is available with numerous Nitrogen and Helium algorithms. Currently over eleven unique algorithms are in the Cochran Algorithm Library.
Stored data is recovered with a Cochran USB Module and the Generation 5 Cochran PC Analyst® software.
There are nine CPU models with a variety of High Pressure transducers and up to three PO2 sensors.
The main component of the Cochran “Lifeguard System” is called the “Lifeguard CPU”. The Lifeguard peripherals are appropriately named and will be briefly discussed herein.

3. CPU Module Models Model C0 No Hp Sensor No PO2 Sensors Model C1
One Hp Sensor
No PO2 Sensors
Model C2
Two Hp Sensors
No PO2 Sensors
Model C3
No Hp Sensors
1 to 3 PO2 Sensors
Negative Volt Input
Model C4
One Hp Sensor
1 to 3 PO2 Sensors
Negative Volt Input
Model C5
Two Hp Sensors
1 to 3 PO2 Sensors
Negative Volt Input
Model C6
No Hp Sensors
1 to 3 PO2 Sensors
Positive Volt Input
Model C7
One Hp Sensor
1 to 3 PO2 Sensors
Positive Volt Input
Model C8
Two Hp Sensors
1 to 3 PO2 Sensors
Positive Volt Input
Model C2 Shown
For size reference

4. Turning the CPU Module On and Off
The Lifeguard CPU Module can be turned on either automatically or manually. Turning it on manually involves shorting contacts #1 and #2 with a metallic object for two or more seconds. For those Modules with Cylinder Pressure Transducers, it will automatically turn on within 16 seconds after it senses a Cylinder Pressure of greater than 200 psi. For Modules WITHOUT any Cylinder Pressure the unit will automatically turn on after 16 seconds if it senses any PO2 Sensor reading greater than 0.30 ATA. As the Lifeguard CPU Module turns on it will issue five one-second beeps as all of its many integrity checks are completed.
If the CPU Modules companion Display Module(s) are within one meter of each other, the Display Module will sense that the CPU Module is on and automatically turn itself on.
If the CPU Module is already on, shorting contacts #1 and #2 will cause the unit to enter the Touch Programming Mode (if it is enabled). If in the Touch Programming Mode (further explained below), the mode will be exited after one minute if no action is taken.
Returning to the Off state is automatic. For those models with Cylinder Pressure Transducers, the unit will turn off 15 minutes after the Cylinder Pressure goes less than 200 psi. For that Module WITHOUT any Cylinder Pressure (the C3 model) the unit will automatically turn off 15 minutes after it senses all PO2 Sensor readings are less than 0.30 ATA which may require that a rebreather loop be opened to the atmosphere.
Even though the Lifeguard CPU Module is in the extremely low power Off State, it continues to monitor and log many parameters such as Altitude, Temperature, and battery voltages. It also continues to compute any Nitrogen and Helium residuals and any Gas Toxicities. This is called “Interdive Profiling”. While Off, the CPU Module does not transmit.
Fifteen minutes after the CPU Module turns off, the companion Display Module will automatically turn itself off.

5. CPU Touch Contacts
To manually turn on the CPU Module, short Contact #1 and Contact #2 with a metal object for two seconds. The Module will issue five beeps as it performs internal checks and turns on.
If the CPU Module is already on, shorting these contacts will cause it to enter the Touch Programming Mode if it is enabled.

6. CPU Module Modes
While On, the CPU Module will be in one of the following dive related Modes:
Surface Mode Dive Mode
Two Minute Warning Mode Decompression Mode
Decompression Surface Mode PostDive Interval Mode
In addition, there are two non-dive related Modes:
Touch Programming Mode PreDive Prediction Mode
The CPU Module automatically switches between these Modes based on algorithmic computations, gas residuals, gas flows and/or depth and time.
When first turned on the CPU Module will enter the Surface Mode and begin computing and transmitting. In this Mode the Module will turn off 15 minutes after the Cylinder Pressure is less than 200 psi and the PO2 is less than 0.30 ata (if it has PO2 sensors).
When the CPU Module goes below 7fsw it will enter the Dive Mode and begin computing and recording profiles at a one second rate. When the CPU Module ascends above 4fsw it will enter the PostDive Interval mode. If a dive is restarted within that interval it will be considered part of the same dive and recorded as such. If the Interval is allowed to expire (typically 10 minutes) the CPU Module will enter the Surface Mode.
When the CPU Module enters a dive it takes a “snapshot” of numerous parameters and stores it as the “Beginning Summary” for that specific dive. When the CPU Module exits a dive it takes a “snapshot” of numerous parameters and stores it as the “Ending Summary” for that specific dive. It also takes a snapshot of the system configuration. There can be a maximum of 8,192 dives of these Summaries.

7. CPU Module Surface Mode (Just after turning on)
When first turned on, the CPU Module will enter the Surface Mode and begin computing and transmitting. The transmitted data includes Surface information and Configuration information. The Configuration information enables the Display Module to be cognizant of the details of the CPU Module’s configuration. During this process of the Display Module obtaining the CPU Module’s configuration, the “SERVICE” legend will be on. When the Display Module has all of the configuration data it needs, the “SERVICE” legend will turn off. This will take one or two minutes. Do not start a dive if the “SERVICE” legend is on.
In the Surface Mode if the Gas Loadings and Oxygen Toxicities are all zero, the diver is considered “Clean” and the Surface Display will be different. If there are Gas Loadings and/or Oxygen Toxicities, the system will re-compute them once per second working them to zero. Current Altitude is considered in these computations.
In the Surface Mode the CPU Module will turn off 15 minutes after the Cylinder Pressure is less than 200 psi and the PO2 is less than 0.30 ata (if it has PO2 sensors).
When the CPU Module goes below 7fsw it will exit the Surface Mode enter the Dive Mode, take a snapshot of the Beginning Summary, and begin computing and recording profiles.

8. CPU Module Surface Mode (Just after turning on)

9. Lifeguard® Dive Computer Tutorial CPU Module Dive Mode
When the CPU Module is in the Surface Mode and goes below 7fsw it will enter the Dive Mode and begin computing and recording profiles at a one second rate. As it enters the Dive Mode it takes a “snapshot” of numerous parameters and stores it as the “Beginning Summary” for that specific dive.
While in the Dive Mode, Gas Loadings and/or Oxygen Toxicities will be re-computed once per second based on numerous parameters. Current Altitude and other environmental factors may be used in these computations dependent upon the algorithm being used.
While in the Dive Mode, if the CPU Module computes that the diver can stay at the current depth for only two minutes or less before needing decompression, it will leave the Dive Mode and enter the Two Minute Warning Mode.
When the CPU Module is in the Dive Mode (no decompression) and ascends above 4fsw it will enter the PostDive Interval Mode. If a dive is restarted within that interval it will be considered part of the same dive and recorded as such. If the Interval is allowed to expire (typically 10 minutes) the CPU Module will re-enter the Surface Mode and take an “Ending Summary” snapshot.

10. CPU Module Two Minute Warning Mode
While in the Dive Mode, if the CPU Module computes that the diver can stay at the current depth for only two minutes or less before needing decompression, it will leave the Dive Mode and enter the Two Minute Warning Mode.
During the Two Minute Warning Mode, the audible
While in the Dive Mode, Gas Loadings and/or Oxygen Toxicities will be re-computed once per second based on numerous parameters. Current Altitude and other environmental factors may be used in these computations dependent upon the algorithm being used.
If the Diver ascends so there is more than three minutes before decompression, the CPU Module will exit the Two Minute Warning Mode and re-enter the Dive Mode.
If the diver stays in this mode until the CPU Module computes that there is no time left before decompression is required, it will exit the Two Minute Warning Mode and enter the Decompression Mode.

11. CPU Module Decompression Mode
If the diver stays in the Two Minute Dive Warning Mode until the CPU Module computes that there is no time left before decompression is required, it will exit the Two Minute Warning Mode and enter the Decompression Mode.
While in the Decompression Mode, Gas Loadings and/or Oxygen Toxicities and Deco Stops and Times will be re-computed once per second based on numerous parameters. Current Altitude and other environmental factors may be used in these computations dependent upon the algorithm being used.
Decompression stops and times will be displayed to assist the diver’s ascent. To achieve the optimum ascent time it is best if the diver stays at or slightly below the recommended stop. However, if the diver does venture shallower, new decompression stops and times will be re-computed every second.
When all of the decompression stops have been satisfied, the CPU Module will exit the Decompression Mode and re-enter the Dive Mode.
When the CPU Module is in the Decompression Mode and ascends above 4fsw with a decompression obligation pending, it will enter the Surface Decompression Mode. Normally, this does not occur unless the diver surfaces with a decompression obligation pending.

12. CPU Module Surface Decompression Mode
When the CPU Module is in the Decompression Mode and ascends above 4fsw with a decompression obligation pending, it will enter the Surface Decompression Mode. Normally, this does not occur unless the diver surfaces with a decompression obligation pending.
While in this mode, Gas Loadings and/or Oxygen Toxicities and Deco Stops and Times will be re-computed once per second based on numerous parameters. Current Altitude and other environmental factors may be used in these computations dependent upon the algorithm being used.
Remaining in this mode exposes the diver to significant risk!

13. CPU Module Post-Dive Interval Mode
When the CPU Module ascends above 4fsw it will enter the PostDive Interval mode. If a dive is restarted within that interval it will be considered part of the same dive and recorded as such. If the Interval is allowed to expire (typically 10 minutes) the CPU Module will enter the Surface Mode.
When the CPU Module enters a dive it takes a “snapshot” of numerous parameters and stores it as the “Beginning Summary” for that specific dive. When the CPU Module exits a dive it takes a “snapshot” of numerous parameters and stores it as the “Ending Summary” for that specific dive. It also takes a snapshot of the system configuration. There can be a maximum of 8,192 dives of these Summaries.

14. CPU Module Surface Mode (After a Dive)
When first turned on, the CPU Module will enter the Surface Mode and begin computing and transmitting. In this Mode the Module will turn off 15 minutes after the Cylinder Pressure is less than 200 psi and the PO2 is less than 0.30 ata (if it has PO2 sensors).
When the CPU Module goes below 7fsw it will enter the Dive Mode and begin computing and recording profiles at a one second rate. When the CPU Module ascends above 4fsw it will enter the PostDive Interval mode. If a dive is restarted within that interval it will be considered part of the same dive and recorded as such. If the Interval is allowed to expire (typically 10 minutes) the CPU Module will enter the Surface Mode.
When the CPU Module enters a dive it takes a “snapshot” of numerous parameters and stores it as the “Beginning Summary” for that specific dive. When the CPU Module exits a dive it takes a “snapshot” of numerous parameters and stores it as the “Ending Summary” for that specific dive. It also takes a snapshot of the system configuration. There can be a maximum of 8,192 dives of these Summaries.

15. CPU Dive Parameters Profiled (page 1 of 2)
Parameter: Models: C0 C1 C2 C3 C4 C5 C6 C7 C8
Depth X X X X X X X X X
Ambient Temperature X X X X X X X X X
Ascent/Descent Rate X X X X X X X X X
Nitrogen Loading X X X X X X X X X
Helium Loading X X X X X X X X X
No-deco Time Remaining X X X X X X X X X
Total Deco Time Remaining X X X X X X X X X
Stop Deco Time Remaining X X X X X X X X X
Port Side Battery Voltage X X X X X X X X X
Starboard Side Battery Voltage X X X X X X X X X
Internal Battery Voltage X X X X X X X X X
O2 Percentage X X X X X X X X X
He Percentage X X X X X X X X X
N2 Percentage X X X X X X X X X
CNS Oxygen Toxicity X X X X X X X X X
Pulmonary Oxygen Toxicity X X X X X X X X X

16. CPU Dive Parameters Profiled (page 2 of 2)
Parameter: Models: C0 C1 C2 C3 C4 C5 C6 C7 C8
Cylinder #1 (O2) Pressure X X X X X X
Cylinder #1 (O2) Gas Flow X X X X X X
Cylinder #1 (O2) Gas Time Remaining X X X X X X
Cylinder #2 (Dil) Pressure X X X
Cylinder #2 (Dil) Gas Flow X X X
Cylinder #2 (Dil) Gas Time Remaining X X X
PO2 Sensor a PO2 Value X X X X X X
PO2 Sensor b PO2 Value X X X X X X
PO2 Sensor c PO2 Value X X X X X X
PO2 Sensor Voted Average PO X X X X X X
Negative PO2 Sensor Input X X X
Positive PO2 Sensor Input X X X

17. CPU Dive Events Recorded
Depth Sensor Failure Altitude over 15,000 feet
Temperature Sensor Failure Depth greater than Set Point
Depth greater than 250 meters
Cylinder #1 Pressure Sensor Failure Cylinder #1 Pressure greater than 5,200 psi
Cylinder #2 Pressure Sensor Failure Cylinder #2 Pressure greater than 5,200 psi
PO2a Sensor Failure PO2a less than Low Set Point
PO2b Sensor Failure PO2a greater than High Set Point
PO2c Sensor Failure PO2b less than Low Set Point
PO2b greater than High Set Point
PO2c less than Low Set Point
PO2c greater than High Set Point
Notes:
Data shown is for Lifeguard CPU Module model C5. Other models may have fewer parameters.
For Diagnostic purposes, many other parameters not shown are stored.
See Cochran’s “Analyst PC Software” document for more details

18. Dive Parameters Standard Specifications
The Lifeguard Recorder Module and the Lifeguard Dive Computer CPU Module are available in two levels of specifications; “Standard” (shown here) and “Extended”. Recreational and Commercial models are optionally available with either. For Military applications only the “Extended” Specification is available.
Parameter: Range: Accuracy: Resolution:
Maximum Operating Depth 600 fsw
Depth 0 to 600 fsw +/- 1% of full scale feet
Max Depth (in air) 10 fsw
Ambient Temperature 0°f to 140°f +/- 2°f 0.5°f
Ascent/Descent Rate 250 fpm +/- 2 fpm 1 fpm
Cylinder #1 (O2) Pressure 5,200 psi +/- 3% of full Scale psi
Cylinder #1 (O2) Gas Flow 0 to 250 lpm +/ lpm lpm
Cylinder #2 (Dil) Pressure 5,200 psi +/- 3% of full Scale psi
Cylinder #2 (Dil) Gas Flow 0 to 250 lpm +/ lpm lpm
PO2 Sensors a, b, and c 0 to ATA Note ATA
Port Side Battery Voltage 0 to 4.00 Volts +/ volts volts
Starboard Side Battery Voltage 0 to 4.00 Volts +/ volts volts
Internal Battery Voltage 0 to 4.00 Volts +/ volts volts
Note 1: PO2 Sensors are further calibrated in the field by the user.

19. Dive Parameters Extended Specifications
The Lifeguard Recorder Module and the Lifeguard Dive Computer CPU Module are available in two levels of specifications; “Standard” and “Extended” (shown here). Recreational and Commercial models are optionally available with either. For Military applications only the “Extended” Specification is available.
Parameter: Range: Accuracy: Resolution:
Maximum Operating Depth 820 fsw
Depth (in water) < 200 fsw +/- 2 fsw feet
Depth (in water) to 400 fsw +/- 3 fsw feet
Depth (in water) > 400 fsw +/- 4 fsw feet
Max Depth (in air) 60 fsw
Ambient Temperature 0°f to 140°f +/- 2°f 0.5°f
Ascent/Descent Rate 250 fpm +/- 2 fpm 1 fpm
Cylinder #1 (O2) Pressure 6,000 psi +/- 3% of full Scale psi
Cylinder #1 (O2) Gas Flow 0 to 250 lpm +/ lpm lpm
Cylinder #2 (Dil) Pressure 6,000 psi +/- 3% of full Scale psi
Cylinder #2 (Dil) Gas Flow 0 to 250 lpm +/ lpm lpm
PO2 Sensors a, b, and c 0 to ATA Note ATA
Port Side Battery Voltage 0 to 4.00 Volts +/ volts volts
Starboard Side Battery Voltage 0 to 4.00 Volts +/ volts volts
Internal Battery Voltage 0 to 4.00 Volts +/ volts volts
Note 1: PO2 Sensors are further calibrated in the field by the user

20. CPU Interdive Profiling
As with all of Cochran’s Dive Computers, the Lifeguard CPU automatically logs certain data even when the unit is “Asleep”. Periodically, it measures a number of parameters to see if any have changed. If something has changed, relevant parameters are logged. Cochran refers to this activity as “Interdive Profiling” and is similar to a Flight Data Recorder. The parameters measured for this purpose are:
Universal Coordinated Time (GMT/Zulu)
Barometric Altitude
Ambient Temperature
Port Battery Voltage
Starboard Battery Voltage
Internal Battery Voltage
Relevant Sensors Integrity
This information is shown to the user via the Lifeguard Analyst® PC Software.
In case of a diver incident, the Lifeguard CPU should be kept with the diver so that it can continue to log altitudes and temperatures to which the diver is exposed during transport. Analyses of the altitudes to which a diver is exposed can be diagnostically very important.

21. CPU Recording Capacity
Number of Dives 8,192
Dive recording sampling rate: Always one sample per second
Total Dive Hours of recording capacity (at one second sampling):
Product C0 = 12,000
Product C1 = 12,000
Product C2 = 9,500
Product C3 = 12,000
Product C4 = 9,500
Product C5 = 8,000
Product C6 = 12,000
Product C7 = 9,500
Product C8 = 8,000
Interdive Profiling: 100,000 samples (Maximum) per dive
Dive Beginning Data Snapshots: 8,192 Over 30 parameters per Dive
Dive Ending Data Snapshots: 8,192 Over 50 parameters per Dive
All data, including high resolution dive profiles can be exported in the .csv format via Analyst software.

22. CPU Dive Beginning Summary Snapshot
Universal Coordinated Time (GMT/Zulu) Current Depth
Current Barometric Altitude Current Ascent/Descent Rate
Surface Time (Since turned on or since last dive) Current Gas Loadings
Complete unit Configuration Current O2 Toxicities
Current Warnings User PO2 Sensor Calibration Information
Ambient Temperature Port Battery Voltage
Starboard Battery Voltage Internal Battery Voltage
Cylinder #1 Pressure Cylinder #2 Pressure
Cylinder #1 Gas Flow Cylinder #2 Gas Flow
PO2a Reading
PO2b Reading
PO2c Reading
Notes:
Data shown is for Lifeguard CPU model C5. Other models may have fewer parameters.
For Diagnostic purposes, many other parameters not shown are stored.
See Cochran’s “Analyst PC Software” document for more details

23. CPU Dive Ending Final Snapshot
Universal Coordinated Time (GMT) Maximum Depth
Average Depth Bottom Time
Total Dive Events Recorded Ascent Rate Analyses
Current O2 Toxicities Current Gas Loadings
Ambient Temperature Port Battery Voltage
Starboard Battery Voltage Internal Battery Voltage
Cylinder #1 Pressure Cylinder #2 Pressure
Cylinder #1 Gas Flow Cylinder #2 Gas Flow
Cylinder #1 Average Gas Flow Cylinder #2 Average Gas Flow
PO2a Reading
PO2b Reading
PO2c Reading
Notes:
Data shown is for Lifeguard CPU model C5. Other models may have fewer parameters.
For Diagnostic purposes, many other parameters not shown are stored.
See Cochran’s “Analyst PC Software” document for more details

24. Some CPU User Settable Options
UCT Time Set from PC Clock or from the Internet
Local Time Setting Local Time determines the number of minutes from UCT Time
Units Metric or Imperial
Gas Flow SAC/DAC (Surface Air Consumption or Depth Air Consumption)
Gas Flow psim/lpm (psi per minute or liters per minute)
Cylinder #1 Size Liters of Water Capacity (determines Gas Flow and Workload)
Cylinder #2 Size Liters of Water Capacity (determines Gas Flow and Workload)
PO2a Sensor Enable/Disable (Tells system to use or ignore this Sensor)
PO2b Sensor Enable/Disable (Tells system to use or ignore this Sensor)
PO2c Sensor Enable/Disable (Tells system to use or ignore this Sensor)
Notes:
Data shown is for Lifeguard CPU Module model C5. Other models may have fewer parameters.
For Diagnostic purposes, many other parameters not shown are stored.
See Cochran’s “Analyst PC Software” document for more details

25. Some CPU User Settable Options
Select active PO2a Sensor (Enabled or Disabled):
Select active PO2b Sensor (Enabled or Disabled):
Select active PO2c Sensor (Enabled or Disabled):
Select Auto Altitude Compensation of PO2 Cal (On or Off):
Enter PO2 Cell Standard 0.21 ata (10 to 25): [In millivolts]
Select Number of PO2 Cal Points (One or Two):
Enter Lower PO2 Cal Point in O2% (18.0 to 30.0): [Only shows if two point Calibration]
Enter Higher PO2 Cal Point in O2% (20.0 to 99.9): [Only shows if two point Calibration]
Enter Single Point PO2 Cal Point in O2% (18.0 to 99.9): [Only shows if one point Calibration]
Notes:
Data shown is for Lifeguard CPU Module model C5. Other models may have fewer parameters.
For Diagnostic purposes, many other parameters not shown are also stored.
See Cochran’s “Analyst® PC Software” document for more details

26. PO2 Sensor System
Lifeguard CPU Module models C3 through C8 have a sophisticated PO2 system that can manage up to three external PO2 sensors. The cable attached to the Lifeguard CPU has a four pin waterproof connector on the end. A mating connector and cable can be supplied to attach to a specific Breathing Apparatus. If the Breathing Apparatus already has PO2 sensors, the Lifeguard CPU can be connected to use those sensors, or it can be connected to independent PO2 sensors. The system is compatible with PO2 sensors like the R22D with a 10 millivolt output or the PSR with a 25 millivolt output.
CPU Models C3, C4, and C5 require a negative PO2 input voltage and models C6, C7, and C8 require a positive PO2 input voltage.
The unique high resolution analog and digital subsystem that measures the PO2 sensors is highly accurate and stable and is individually calibrated at the factory to a high precision. Furthermore, changes in Battery voltages do not affect the PO2 measurements or calibration. However, the PO2 Sensors themselves can be unstable and age over time. Therefore, the PO2 sensors require periodic calibration in the field. To make this quick, easy, and simple, it is recommended to use the free Cochran Analyst® 5 PC Software. Analyst® also allows the user to select Automatic Altitude Compensation and one or two point calibration method, among others.
After the high precision PO2 Sensors measuring system, numerous checks are performed once every second to ensure the continuing integrity of the sensors.
As an alternative, the PO2 sensors can be calibrated via “Touch Programming”.
Contact Cochran to discuss your specific requirements.

27. PO2 Calibration (page 1 of 2)
The Lifeguard PO2 Calibration is simple and fast. After connecting the Lifeguard to the Analyst USB cable and establishing the connection, the operator selects PO2 Calibration on the Analyst screen. Analyst then queries the Lifeguard once per second and displays the following information (updated once per second):
Current PO2a Sensor Voltage Reading (No Entry): millivolts
Current PO2b Sensor Voltage Reading (No Entry): millivolts
Current PO2c Sensor Voltage Reading (No Entry): millivolts
Current PO2a Sensor PO2 Reading (No Entry): ata
Current PO2b Sensor PO2 Reading (No Entry): ata
Current PO2c Sensor PO2 Reading (No Entry): ata
For the Single Point Calibration method, the user first enters the “Single Point PO2 Cal Point in O2%”, for example: “92.3”. If this is already the correct percentage there is no need to re-enter it. Next, the user exposes the PO2 sensors to the Oxygen source and observes the Analyst screen until the readings are reasonably close and stable. Clicking on the “CAL” button will automatically perform the calibration.

28. PO2 Calibration (page 2 of 2)
For the Two Point Calibration method, the user first enters the “Lower Point PO2 Cal Point in O2%”, for example: “21.0”. If this is already the correct percentage there is no need to re-enter it.
Next, the user exposes the PO2 sensors to this LOWER Percentage Oxygen source and observes the Analyst screen until the readings are reasonably close and stable. Clicking on the “PRE-CAL” button will lock in the first parameters for the calibration.
Next, the user enters the “Higher Point PO2 Cal Point in O2%”, for example: “91.5”. If this is already the correct percentage there is no need to re-enter it.
Next, the user exposes the PO2 sensors to this HIGHER Percentage Oxygen source and observes the Analyst screen until the readings are reasonably close and stable. Clicking on the “CAL” button will automatically perform the calibration. Continue to monitor the Analyst screen for PO2 stability and completion status.
Note:
For either Calibration Method, Calibration is instantaneous but the user should briefly continue to monitor the Analyst screen for PO2 stability and completion status. Each set of Calibration Parameters is stored in the Lifeguard CPU as an Interdive Event.

29. PO2 Sensors Connections
Lifeguard CPU models with a PO2 sensor cable allow up to three PO2 sensors to be connected. The cable attached to the Lifeguard CPU has a four pin waterproof connector on the end. A mating connector and cable can be supplied to attach to a specific Breathing Apparatus. If the Breathing Apparatus already has PO2 sensors, the Lifeguard CPU can be connected to use those sensors, or the Lifeguard CPU can be connected to independent PO2 sensors.
A “T” is available that contains a single PO2 Sensor. The “T” can be inserted in the inhalation hose of a rebreather.
The Lifeguard is available to accommodate either positive or negative PO2 Sensor voltage.
Contact Cochran to discuss your specific requirements.

30. Gas Flow
Gas Flows are computed any time the unit is on by monitoring the change in cylinder pressure to a very high degree of precision. The sampling rate of this monitoring is once per second. The computations for gas flow are based on a 60 second running average.
Changes in the temperature of a cylinder can affect actual pressure within the cylinder. For that reason, the High Pressure Sensor also measures the cylinder temperature. This allows the Lifeguard to compensate for any changes in cylinder temperature.
The Gas Flow computations are based on the user selection of:
DAC (Depth Air Consumption) or
SAC (Surface Air Consumption).
Gas Flow is also based on the user selection of:
psim (PSI per minute) or
lpm (liters per minute).
For accurate lpm computations and diver workload it is important that the Cylinder size be properly set.
User selections are put into the Lifeguard via the Lifeguard Analyst PC Software.

31. Gas Flow
DAC (Depth Air Consumption) is the actual gas consumption regardless of depth. DAC measurement can be either psim (PSI per minute) or lpm (liters per minute). If a certain amount of gas is being consumed while at the surface, diving to one atmosphere (33 fsw) will double the measurement because twice as much gas is being consumed. Typically, this is used when the actual gas used is to be profiled.
SAC (Surface Air Consumption) is the actual gas consumption referred to the surface. Basically, SAC is DAC with depth removed from the computation. SAC measurement can be either psim (PSI per minute) or lpm (liters per minute). If a certain amount of gas is being consumed while at the surface, diving to one atmosphere (33 fsw) will not change the measurement. Typically, this is used when comparing gas flows between divers.
lpm (liters per minute) is the volume of gas consumed. For the Lifeguard to automatically convert from a decline in cylinder pressure to the volume consumed it is necessary for the system to know the size of the cylinder in liters. This is commonly called “Liters of Water Capacity”. To convert from a cylinder size in cubic inches to liters the following table may be helpful.
Changes in the temperature of a cylinder can affect actual pressure within the cylinder. For that reason, the High Pressure Sensor also measures the cylinder temperature. This allows the Lifeguard to compensate for any changes in cylinder temperature.

32. Cubic Feet to Liters Conversion Table
Aluminum
13 cuft = 1.9 liters
19 cuft = 2.7 liters
30 cuft = 4.4 liters
40 cuft = 5.8 liters
50 cuft = 7.2 liters
63 cuft = 9.0 liters
72 cuft = 10.4 liters
80 cuft = 11.1 liters
85 cuft = 11.8 liters
100 cuft = 13.2 liters
LP Steel
50 cuft = 8 liters
85 cuft = 13 liters
95 cuft = 15 liters
108 cuft = 17 liters
120 cuft = 19 liters
HP Steel
71 cuft = 9 liters
80 cuft = 10.2 liters
100 cuft = 12.9 liters
117 cuft = 15.0 liters
120 cuft = 15.3 liters

33. PO2 Sensors Voting Algorithm
For the Lifeguard CPUs and Lifeguard Recorders with PO2 Sensor capability the following applies. Via the ANALYST® PC Software, the user can enable or disable any combination of the three PO2 Sensors. Only those PO2 Sensors that are enabled are included in the Voting Algorithm. If an enabled PO2 Sensor is found to be outside of the acceptable range, it will be automatically disabled by the system.
With three enabled and in-range PO2 Sensors, the system first determines the difference between all combinations of the three PO2 Sensors. The PO2 Sensor that has a reading difference that is the greater than the others will have its reading discarded. The remaining two readings will be averaged to provide a single PO2 that can used.
With two enabled and in-range PO2 Sensors, the system first determines the difference between the two sensors. These two readings will be averaged to provide a single PO2 that can used.
With only one enabled and in-range PO2 Sensor, the system will use this PO2 reading.
If in the PO2 Mode using PO2 Sensors and all PO2 Sensors fail, the system will automatically switch to the FO2 Mode. In this Mode, the Deco/Gas Algorithm is not driven by the MEASURED PO2, but is driven by the COMPUTED PO2. This computed PO2 is determined by the FO2 Gas Switching algorithm which is configured by the user and includes Depth, Time, Gas percentages parameters for up to eight Gas Switches.

34. Hands-free Gas Switching
To be included in a later version of this Tutorial.

35. Touch Programming
To be included in a later version of this Tutorial.

36. Pre-dive Planning Mode
To be included in a later version of this Tutorial.

37. Attaching the HP Sensor(s) to a Breathing Apparatus
For those Lifeguard CPU models with high-pressure (HP) sensors, they install into a high-pressure port of your first-stage regulator.
Remove the HP plug from your first stage regulator.
Lightly lubricate the sensor O-ring only with a lubricant approved for use with Enriched Air Nitrox equipment. DO NOT USE SILICONE GREASE.
Screw the sensor lightly into the HP port
Using a Scuba Tool, or thin 9/16" open-end wrench, snug the HP sensor connection taking caution to not over tighten.
CAUTION: Tools such as vise-grips or channel lock pliers will damage the sensor.
CAUTION: DO NOT use your hand to tighten the high-pressure connection. This procedure must only be accomplished by using the appropriate tool placed over the metal nut of the high-pressure connection. It must not be over tightened.
CAUTION: DO NOT twist, stress, or otherwise abuse the HP cable.
With the first stage properly attached to a filled SCUBA cylinder, slowly open the cylinder valve. Once the valve has been opened, listen to the HP connection for any escaping gas. If possible, completely immerse the system in water to see if bubbles form around your connection. If any gas leak is seen or heard, immediately turn the gas off by closing the cylinder valve.
Usually, the Lifeguard clips to a low-pressure hose close to the first-stage. When clipping it onto the low-pressure hose, a rolling motion will provide better results rather than pushing it straight down onto the hose.

38. CPU Attaching the HP Sensor(s) to a Breathing Apparatus
The standard length of the HP cable is 13 inches. Other cable lengths can be specified when purchasing the Lifeguard CPU Module from Cochran.
If a spare HP port is not available, an HP Port
Extender is available which creates an extra HP port.
It is available with different thread options.
A 360 degree HP swivel is available that can make
installation simpler in difficult situations. It is
particularly useful with the Lifeguard models with two
HP Sensors.

39. CPU Module Batteries
The Lifeguard CPU Module is powered by two user-replaceable, off the shelf, three volt type CR12600SE Lithium batteries. The two batteries are redundant where the electronics system automatically draws power from the battery that has the highest voltage. Should both of these main batteries be depleted, an internal battery takes over and an orderly shutdown is executed. This internal battery has an expected life of over ten years. In normal operation, for the original owner, this internal battery will be replaced free of charge at the factory every ten years.
When replacing the main batteries, it is recommended to replace one, then the other so the Module will always have power. If this procedure is followed and the batteries are not completely depleted, replacing the batteries does not affect any parameters within the unit such as Nitrogen loading. Never replace just one battery. It is recommended that both batteries be replaced.
With fresh Lithium batteries, the shelf-life of the batteries is over ten years. In average use the batteries will last for over 1,000 hours of diving or two years, whichever occurs first. However, it is recommended to replace the batteries annually. Never store the CPU Module with low or depleted or removed batteries.
For maximum reliability and battery life we recommend Lithium batteries. However, Alkaline “N” cells will also work but at reduced life and reliability. When using “N” cells, always replace the two Lithium batteries with four new “N” cells.
The battery voltages can be seen on the Lifeguard Display Module or by using the Analyst PC software Version 5.0..
Note: The Lithium battery is non-magnetic and will not affect a compass. Most Alkaline “N” cells are magnetic.
CAUTION: Never use the 12 volt battery that is similar in size to the 1.5 volt “N” cell!

40. Replacing Recorder and CPU Module Batteries
The CPU Module main batteries are very easy for the user to replace as there are no chargers, wires, holders, or special tools needed. Each battery has its own watertight compartment that is sealed from the electronics. The compartment is accessed by unscrewing its Cap with a coin (a US Quarter is supplied with the product). Each Cap has two o-rings for watertight redundancy. The contacts in the Battery Caps and Compartments are of a unique metal that resists seawater corrosion. Should a compartment become flooded, immediately and thoroughly flush the compartment and cap with fresh water, let it dry, and replace the battery. Be sure to carefully inspect the Cap for debris before installing it. The Cap is a special material that is softer than the Case material so that the Cap will be expelled should pressure build up within a Compartment.
CAUTION: Observe proper polarity when installing batteries! The positive tip goes in first.
Tighten battery caps until the o-rings cannot be seen.
Never overtighten the caps.
Only use the supplied U.S. Quarter or similar coin. Never use a screwdriver.

41. Display Modules Battery
The Lifeguard Computer Displays D1 and D3 Modules and Team Module T1 are powered by one user-replaceable Lithium battery three volt Type CR12600SE.
With a fresh Lithium battery, the shelf-life of the Module is ten years. If diving, the battery life depends on the use of the backlight “Taclite”. If only occasionally using the Taclite, the batteries will last for over 1,000 hours of diving or two years, whichever occurs first. However, it is recommended to replace the batteries annually. If the Taclite is turned on for 100% of a dive, the battery life will be over 50 hours of diving. The Taclite turns on every time the case is tapped and the amount of time the Taclite stays on can be changed with the Analyst software or by using Touch Programming. From the factory, the Taclite Dwell Time is set for 10 seconds.
For maximum reliability and battery life it is recommend to use Lithium batteries. However, Alkaline “N” cells will also work but at reduced life and reliability.
For average use the batteries will last for over 1,000 hours of diving or two years, whichever occurs first. However, it is recommended to replace the batteries annually
The battery voltages can be seen on the Lifeguard Display Module or by using the Analyst PC software.
Note: The Lithium battery is non-magnetic and will not affect a compass. Most Alkaline “N” cells are magnetic.
CAUTION: Never use the 12 volt battery that is similar in size to the 1.5 volt “N” Cell.

42. Replacing Display Modules Battery
The Lifeguard Computer Display and Team Modules battery is very easy for the user to replace as there are no chargers, wires, holders, or special tools needed. The battery has its own watertight compartment that is sealed from the electronics. The compartment is accessed by unscrewing its Cap with a coin (a US Quarter is supplied with the product). The Cap has two o-rings for watertight redundancy. The contacts in the Battery Caps and Compartments are of a unique metal that resists seawater corrosion. Should a compartment become flooded, immediately and thoroughly flush the compartment and cap with fresh water, let it dry, and replace the battery. Be sure to carefully inspect the Cap for debris before installing it. The Cap is a special material that is softer than the Case material so that the Cap will be expelled should pressure build up within a Compartment.
CAUTION: Observe proper polarity when installing battery! The positive tip goes in first.
Tighten battery cap until the o-rings cannot be seen.
Never overtighten the cap.
Only use the supplied U.S. Quarter or similar coin. Never use a screwdriver.

43. CPU Module Warranty and Support
For Recreational use, the Cochran Lifeguard CPU has a two year Limited Warranty. For Commercial and Military use it has a one year Limited Warranty. Download the Warranty details from our Website. All Models include USB interface and Standard Edition of the Analyst® PC Software.
We are committed to professional, responsive support for the lifetime of our products. Phone during our office hours in Dallas, Texas or Visit our Website for details.
The Cochran Lifeguard® Products can be purchased from Cochran or selected Distributors and Dealers.

44. Lifeguard Peripherals
“Not Just Another Dive Computer”

45. LCD Receiver-Display Peripheral – D1 Receiver and LCD Display
The Receiver-Display Module peripheral is the primary means of communicating dive information to the diver. It is typically worn on the divers wrist but is also available in hose-mount and retractor-mount configurations. This is usually referred to as the “Lifeguard Display Module”.
The Module receives data transmitted from a Lifeguard CPU Module that have matching addresses and are within a one meter radius of each other.
The Module is fully automatic with no task loading and no buttons. It even automatically turns itself on and off. It has an on-demand LED backlight (“Taclite”) with user selectable colors: Red, Orange, or Amber. The Taclite is turned on by tapping or bumping the case and turns on for ten seconds. This “On Time” can be changed by the user. The intensity of the Taclite is intentionally low so it can be seen by the diver but cannot be seen from the surface. The trans-flective display can be seen in even the brightest sunlight.
It is powered by one user replaceable battery that typically provides over two years of reliable operation. There are no rechargeable batteries to wear out, and no battery chargers to lose.
Model D1
Receiver and LCD Display

46. LCD Teams Receiver-Display Peripheral - T1
The Teams Receiver-Display peripheral allows one diver to monitor the dive parameters of a number of divers in his “Team”. There can be any number of divers in a “Team” and any number of “Teams” on a given Mission. There is no cross-talk between Teams or Team Members. It is typically worn on the divers wrist but is also available in hose-mount and retractor-mount configurations. This is usually referred to as the “Lifeguard Team Module T1”.
The Team Module receives data transmitted from any Lifeguard CPU Module that has matching addresses and are within a one meter radius of each other. This Team Display Module recognizes the six CPU Module type it is communicating with and assumes its specific personality. Up to 64 unique addresses can be set into this Module so that it can recognize up to 64 Lifeguard CPU Modules.
The Module is fully automatic with no task loading and no buttons. It even automatically turns itself on and off. It has an on-demand LED backlight (“Taclite”) with user selectable colors: Red, Orange, or Amber. The Taclite is turned on by tapping or bumping the case and turns on for ten seconds. This “On Time” can be changed by the user. The intensity of the Taclite is intentionally low so it can be seen by the diver but cannot be seen from the surface. The trans-flective display can be seen in even the brightest sunlight.
It is powered by one user replaceable battery that typically provides over two years of reliable operation. There are no rechargeable batteries to wear out, and no battery chargers to lose.
Model T1
Multi-diver Teams Receiver and LCD Display

47. Cochran Consulting, Inc.
ISO 9001:2008
Cochran Consulting Office:
1758 Firman Drive FAX:
Richardson, TX 75081
Websites: