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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

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Thanks!