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Trackmate cable length record?
Posted: Tue Aug 12, 2008 11:21 am
by Toby Warg
I set up my system with 1320 meters to one switch and about 25 meters to the other one. It worked without a problem until the rain came and one of the tapeswitches shortcut.
Is this the longest cable anybody tried so far?
I am interested in knowing about the limit of the system, since we use it for downhill too.
Posted: Tue Aug 12, 2008 11:57 am
by Donald Campbell
we are talking about electrical impulses here.
you should ask any electrician to get detailed info,toby
Posted: Tue Aug 12, 2008 12:53 pm
by Toby Warg
Donald Campbell wrote:we are talking about electrical impulses here.
you should ask any electrician to get detailed info,toby
Of course, but theory and practice are not always best friends.
Posted: Tue Aug 12, 2008 6:14 pm
by Pat Chewning
I have run timing systems with over 4000 ft of wire (Trackmate and Chronocone). Both worked fine.
Ski race systems run with wire over 3 miles long.
I don't think we are coming close to the limits, as long as the timer is imune to the noise and the additional capacitance loading of very long cables.....
Posted: Tue Aug 12, 2008 11:00 pm
by Sj Kalliokoski
Question is mainly how system checks switch, is it constant flow of current or does it look just for voltage, if first one then cable can be long. In both cases cable cam be long but there is slight time shift compared to real times related later case but even then times can be compared to each other.
Posted: Wed Aug 13, 2008 1:55 am
by Pat Chewning
In both systems, the active timing pin is pulled to +5V by a pullup resistor. No current is flowing thru the wires or the switch until the racer hits the switch.
When the racer hits the switch, the current flows from the active pin to ground (the other wire in the system). This pulls the voltage to 0V (through the pullup resistor), and the wires, indicating a START or FINISH event.
The amount of time this takes is (negligibly) affected by the cable length. It will be proportional to the incremtal resistance of the cable (not the resistance of the pull-up resistor), and the incremental capacitance of the cable.
This is usually on the order of 1.0 vs 0.9 times the speed of light over the cable distance.
This can be ignored.
Posted: Wed Aug 13, 2008 11:56 am
by Toby Warg
Pat Chewning wrote:I have run timing systems with over 4000 ft of wire (Trackmate and Chronocone). Both worked fine.
Ski race systems run with wire over 3 miles long.
I don't think we are coming close to the limits, as long as the timer is imune to the noise and the additional capacitance loading of very long cables.....
Good to hear.