MK2 Adaptor

The following picture shows the DIN fitting and the oxygen sensor port. The thing under the sensor port is a dust cap for the sensor, which is a modified grommet.

The Design

My design for the sampling adaptor is based around a simple physical principle - the Venturii Effect. Rather than go into a long winded explanation about pressure differentials and the such, it's easier to demonstrate the effect. Take a plastic T piece and blow through one of the in-line holes. If you hold a piece of lightweight paper close to the offshoot piece, the paper will be drawn to the hole. This is the Venturii Effect.
This principle is used to remove latent gas from the sensor and replace it with nitrox during the sampling process.
In addition to this, I resticted the one open end with a kind of exhaust system. This has the effect of holding the gas to be sampled in the adaptor for a lot longer than if the end were totally open - making sampling a walk in the park.
Some other designs I've seen have the oxygen sensor directly opposite the cylinder inlet. Personally, I don't like this as any crap that is in the pillar valve or the adaptor will get hurled straight at the oxygen sensor - not much fun if that crap happens to be water.

Making the sampling adaptor

To make the above adaptor, you'll need the following bits:-