Instruction manual

Copyright ©2006 Diamond Traffic Products
ALL RIGHTS RESERVED
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3) The first axle is detected with no problem.
4) The second axle (the first axle of the first tandem pair) hits the road tube. This causes FOUR sound waves to
be generated, TWO from each tire.
5) The Left Tire will send two sound waves from it (1 in each direction) and the Right Tire will send two waves from
it as well. The sound waves look something like the following:
-- -- A o B -- -- -- -- -- -- -- -- C o D -- -- -- -- (to Phoenix II)
Each letter represents a sound wave and the arrow next to the letter shows the direction the sound wave is
traveling.
6) At this point the following things will happen: Sound “A” will travel to the end of the road tube and be absorbed
by the plug. Sound “B” and “C” will travel towards each other, collide and be seriously weakened. Sound “D”,
however will be uninhibited and travel down the road tube towards the air switch on the Phoenix II.
Since all of the sound waves except “D” have been destroyed, we will only talk about sound wave “D” for the
rest of this section, and it will be called the Wave.
7) The road tube had been stretched about 50”, so it is now 54.16’ long. Presuming the truck is in the center of the
lane (lane being 12’ wide) and the truck is 8feet wide, the Wave should start at the 44’ mark.
8) The wave will travel down the road tube towards the Phoenix II and contact the air switch in about 39ms (ms
stands for milliseconds, or thousandths of a second).
9) After the Wave hits the air switch, it will bounce back and return up the road tube towards the vehicle. Thus, we
have a weakened returning wave going back up the road tube.
10) The next axle on the truck hits the road tube about 56ms after the first (a 4.5ft spacing typical, on a 55mph
vehicle). Once again, another sound wave “D” is generated and travels down the road tube towards the air
switch.
11) At this point we have the following:
-- -- D2 -- -- -- -- -- -- -- D1 -- -- -- -- -- -- -- -- Phoenix II
One wave traveling down and one weaker wave returning. They will, of course, collide into each other at some point in
the road tube, weakening both waves so that the second wave is too weak to register as an axle strike.
The question then becomes, if this is causing missed axles, why does a shorter road tube work better? If you take a 30’
road tube, stretch it 50”. Sound wave “D” will start about the 24’ mark and therefore will take only 21ms to reach the air
switch. Similarity, sound wave “D” will only take 21ms to return to the starting point (at the 24’ mark). This makes the
total time only 42ms for the first sound wave “D” to strike the air switch and return to the starting point.
This time is BEFORE the 56ms time it takes for the next axle to hit. Therefore, the first sound wave “D” is past the point
of origin and cannot interfere with the next axle strike.
In summary, you are better off using shorter road tubes for faster speed vehicles. You are also better off using shorter
road tubes for vehicles which have closer axle spacing (such as truck tandem axles). To minimize missing axles and
maximizing accuracy we suggest using the following road tube lengths:
Speed
Road Tube Length
0-25 mph
60 ft
26-35 mph
50 ft
36-45 mph
40 ft
46+ mph
30 ft
While a shorter tube at faster speeds is always more accurate, we do not suggest using road tubes shorter than 30’ due
to potential damage to an air switch by very strong “sounds” (or signals).