1. Cochran Consulting, Inc.
5 October 2015
Cochran Consulting, Inc.
Introduction
PO2 Sensor Factors
PO2 Sensor Tee Installation

2. Introduction
The Cochran Lifeguard Recorders and Lifeguard CPU Dive Computers are available in models that are compatible with external PO2 Sensors with positive or negative output PO2 sensors.
The Lifeguard Recorders R3, R4, and R5 accept negative output sensors while the R6, R7, and R8 accept positive output sensors. The Lifeguard CPU Dive Computers C3, C4, and C5 accept negative output sensors while the C6, C7, and C8 accept positive output sensors.
All of these models have a four conductor PO2 cable attached and the other end has a waterproof connector. One contact is common (ground) and the other three are inputs from the outputs of up to three PO2 sensors.
This Lifeguard ‘Tee’ is designed to provide a negative voltage output and is compatible only with the R3, R4, R5, C3, C4, C5 Lifeguard models. It is intended to be used with a single PO2 Sensor “PSR NM”.

3. Important Factors
The Lifeguard Recorders and Dive Computers that have PO2 Sensor capability all can accommodate up to three PO2 Sensors. When using the PO2 Sensor Tee, only one PO2 Sensor (PO2 Sensor ‘a’ ) is used, the other unused PO2 Sensors (PO2 Sensors ‘b’ and ‘c’) should be disabled via the Lifeguard Analyst 5 PC Software. This will prevent the system from flagging the unused PO2 Sensors as malfunctioning and issuing false warnings. See the Lifeguard Analyst 5 Tutorial for details on how to do this.
The Lifeguard PO2 Sensor Tee does not provide any loading on the PO2 Sensor within the Tee. Any loading is provided internally to the attached Lifeguard module. Standard loading is 12k ohms, but custom loading values of 14k ohms or less is available. Contact Cochran for more details.
All PO2 Sensor compatible Lifeguard modules have their Sensor Measuring subsystem calibrated at the factory to a high degree of accuracy and stability. This means that the user only needs to calibrate for changes in the PO2 Sensor itself. Furthermore, because the PO2 readings are not affected by changes in battery voltage, fewer field calibrations are required. In addition, there is a user-selectable option that allows the system to automatically compensate for altitude during field calibration.

4. PO2 Sensor and Tee Install
Pictured is a close up of the completed assembly
of the Tee, PO2 sensor, cap and cable inserted into
the Inhalation Hose.
The Tee is bidirectional and can be installed with the
Cable pointing in either direction.
The Tee has a large inside diameter and does not affect
The breathing characteristics.
The assembly inserted into the Inhalation hose
showing the cable direction toward the rebreather unit
hose attachment.
It is critical that the Tee be installed in the INHALATION
hose.

5. PO2 Sensor and Tee Install
Pictured is the tee, PO2 sensor and
cap that includes the sensor
connector and external connector.
The PO2 sensor lead connector will be
tucked under the wire tied part of the leads,
as shown.

6. PO2 Sensor and Tee Install
Connect the PO2 sensor connector
to the connector inside the cap.
Turn the PO2 sensor over on top of the
cap and align the connector with notches
inside the cap. Lower the PO2 sensor
onto the cap.

7. PO2 Sensor and Tee Install
Turn the cap and PO2 sensor assembly
upright, making certain the sensor,
cap and connector line up with each other.
Wrap two turns of Teflon tape onto
the threads of the cap.

8. PO2 Sensor and Tee Install
As a unit, place the PO2 sensor and
cap assembly into the tee. The PO2
sensor wires will touch both sides
of the tee.
Lower the PO2 sensor and cap assembly
completely into the tee where the threads
start to engage.

9. PO2 Sensor and Tee Install
Thread the cap into the tee. The PO2 sensor will turn with the
cap, so the wires will not be twisted. The external connector
should be aligned with the tee so the PO2 cable will align with
the hose in which the tee is inserted.
The PO2 sensor cable will attach to
the four pins of the cap connector.

10. PO2 Sensor and Tee Install
The cable is fully mated with the
cap connector.
The locking sleeve is threaded onto
the cap connector until tight.

11. Cochran Consulting, Inc.
ISO 9001:2008
Cochran Consulting
1758 Firman Drive
Richardson, TX 75081
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