...Rebreather controller

The HUD...

 

The Head Up Display on the Deep and Altus Pursuit is primarily an independent PO2 monitor. When we say independant, we really mean it. Power supplies, physical compartment and calibration are all separate from the controller or any handset. This means that a single handset and HUD gives you complete redundancy.
Before explaining the display of the HUD, we would like to explain that there are "bad" alarms and "good" alarms. For example a fire bell is a bad alarm. It is bad because the absence of a ringing bell doesn't mean there is no fire. It just means the alarm isn't ringing. The fire bell may not be ringing because the battery is dead or the smoke detector isn't in the right place ........
It doesn't mean that everything is ok.
A good alarm is one where there is an obvious difference between the lack of function and the lack of an alarm. A solid green light doesn't do that so we didn't use one.

In order to be a PO2 monitor, we must be able to read actual PO2 from the device. LED's have been used before to display PO2 by flashing to correspond to the sensor output. Using one LED means we have to wait and remember a sequence that must happen three times before we can make a judgement. The three LED's on the Pursuit indicate the PO2 simultaneously and in time with each other. This gives us a clear indication of both the PO2 and any deviation without having to do much thinking.

The LED's are tricolour and indicate one green flash for each point above a PO2 of 1.0 and one red flash for each point below 1.0
Below are examples of the display modes of the HUD.

Three green flashes indicates the PO2 is 1.3 on all three cells

 

This example demonstrates how easy it is to see a sensor that is out. Even without counting the flashes you can see there is a variation.