On 9/07/2014 7:34 AM, Denny Esterline wrote:
> As Bob eluded - it's not a wire - it's a hose. One end of the hose is
> capped and the sensor on the other end watches for a pressure change.

On the ones I've seen, the far end of the air tube is not sealed. There=20
can be a vent plug to stop  critters entering or sometimes the tube end=20
is simply tied in a loose knot.  The pressure sensors in the roadside=20
box are quite sensitive.

Over here the tube spacing is usually 1 metre, but the roadside unit can=20
be set to other spacings if required.

The roadside unit just counts (time stamped) axle hits for the A & B=20
tubes.  Once the data has been retrieved PC software uses various rules=20
to work out direction, speed, likely vehicle type, etc.   It's not 100%=20
accurate, but fine for general traffic analysis.
David...

--=20
___________________________________________
David Duffy        Audio Visual Devices P/L
Unit 8, 10 Hook St, Capalaba 4157 Australia
Ph: +61 7 38235717      Fax: +61 7 38234717
Our Web Site: www.audiovisualdevices.com.au
___________________________________________

--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.