Many thanks Paul. I'll give it a try.

I have a car fitted with these wheel speed sensors;
http://www.kasensors.co.uk/KA-SP-wheel-speed-sensor.pdf

They were purchased for a different application and as such are NPN type sensors so therefore I believe not directly compatible with the DL2 logger that I have.

How would I go about connecting these sensors to the DL2?

Regards
Jake