Post on 30-May-2020
Trouble Shooting Loops
Dan Inabnitt, CPMKentucky Transportation CabinetNATMEC 2004 San Diego, CaliforniaJune 27-30, 2004
Trouble Shooting LoopsTrouble Shooting Loops
A count is not worth getting injured!In the United States, 120 to 130 workers
die each year in road construction activities.
Of this total, approximately 23% of the fatalities are due to pedestrian workers
being struck by traffic vehicles. Source: The National Work Zone Safety Information Clearinghouse
SAFETY
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OverviewVehicle Detector HandbookSimplified Loop OperationItems to watch forStart with easiest firstRepairReplace Loop
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Moredetailsthanmost couldever use!
Traffic Detector Handbook
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Publication No. FHWA-IP-90-002
http://www.fhwa.dot.gov/tfhrc/safety/pubs/Ip90002/IP90002.pdf
To get the Traffic Detector Handbook
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it’s a wire!inductance is monitoredchange in inductance = detectiondetection = vehiclevehicle = countcount = detector and counter are working!
Simplified loop operation theory
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detector
NO Change in
INDUCTANCE
detector
INDUCTANCE
CHANGEOFF ON
Signal sent to counter
Basic Loop Operation
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Source - Traffic Detector Handbook page 107
Typical Loop Schematic
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loop
recorder
lead-in
detector
harness
connection
splices
Usually enclosed cabinet or
above ground j-box
Usuallybelowground
conduit andj-box
In roadway
Usuallyreferred
to as“homerun”.In shoulder and lanes.(twisted)
Terminal stripbutt splices, etc.
Usuallyin conduit(twisted,
shielded & grounded)
Loop Block Diagram
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How do I determine if I
have a problem and if I
do, what is the cause
and how do I fix it?
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What to watch for…
Single loopsIs it counting any vehicle?
Is it counting each vehicle?
Is it counting each vehicle only once?Especially watch high bodied trucks
Count several vehicles and match count
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What to watch for…
Double loopsAre they counting each vehicle?
Are they counting each vehicle only once?
Do speeds look reasonable?
Do lengths look reasonable?
Count several vehicles and match count
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Site problems could effect operationRebarOverhead structuresPower LinesAdjacent loops
Try adjusting sensitivity settings
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Components to check...counter
detector
harness/connections
lead-in
splices
loop
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Start with easiest first-
-basic troubleshooting
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Visual Inspection of Roadway
Cracks across saw cuts
Broken wires out of saw slot
Underground utility construction
The milling machine---
(a.k.a - THE LOOPEATER!)
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Counter or Detector?Switch to a working “channel”
Try another known good counter/detector
Double loops
If in pairs, reverse pairing
Separate channels to see if each is counting then
compare totals after a few vehicles to determine if
one is not working correctly
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Use multi-meter to check...continuity
inductance
simple ground test
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Harness and other terminals
disconnect from detector
use pin out adapter
alligator clip adapter
check terminals and splices
replace with known good harness
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Check at Junction box splices
Is there water in splice?
Perform same test as in cabinet
If good at j-box replace lead-in
If bad in j-box, problem is in roadway
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If you can determine that the
loop wire or lead-in is broken and
can find the break,
you may be able to splice it.
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Check Current ConditionsIs it still needed?
Will a non-intrusive technology work?
Check for upcoming construction
Check Inventory RecordsPhoto of site
Specifications
Past inspections
Loop Replacement Before Installation...
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Site Selection
good pavement
nearby structures
overhead power
rebar
new development potential (new businesses, subdivisions, etc.)
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Materials
wiresealantlead-in cablewaterproof splice kitswire numbers
number EVERYTHING! conduitjunction boxes
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Procedure
depth
corners
cleaning
twisted lead-ins
splices
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Numbers will aid future troubleshooting
Waterproof splice kitOff Road Wiring
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It is a lot of work!
Do it right!
and
BE SAFE!
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Summary
Vehicle Detector HandbookSimplified Loop OperationItems to watch forStart with easiest firstRepairReplace Loop
Trouble Shooting LoopsTrouble Shooting Loops
Thanks!