Ongoing Detector Issues

A continuous investigation into the potential causes and possible solutions to the issue of high degrees of saturation being recorded by loops that in all respects appear to be functioning correctly.

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Gratuitous Auckland Traffic Light

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Review

• The incidents of chattering and detector lock on can be minimised by maintaining consistent firmware across the controller.

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Review

• The incidents of chattering and detector lock on can be minimised by maintaining consistent firmware across the controller.

• Feeder cables in common use in NZ have not complied with AS/NZS2276 and have no hydrophobic properties.

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Review

• The incidents of chattering and detector lock on can be minimised by maintaining consistent firmware across the controller.

• Feeder cables in common use in NZ do not comply with AS/NZS2276 and have no hydrophobic properties.

• The currently accepted method of testing detector loops is to measure the DC resistance values

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The high DS reading

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Step 1 – Loop condition survey

• Full loop condition survey• Visual inspection of each loop• Visual inspection of road condition• DC insulation test of loop circuit from cabinet• DC resistance of loop from cabinet• DC insulation test of loop circuit from KJB• Re-terminate loop terminations (including changing

feeder cores where possible)• Check and record loop sensitivity• Check and record loop impedance

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The quadrupole scats loop

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Step 2 – Firmware upgrade

• The firmware suite on all controllers was upgrades to the latest V3.49

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Step 2 – Firmware upgrade

• The firmware suite on all 10 controllers was upgrades to the latest V3.49

• There was NO measureable improvement

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Step 3 – Replacement of feeder cables

• Three feeder cables measured marginal for insulation resistance.

• All three cables were replaced.• The high DS values for one loop were

resolved with the replacement of the feeder cable.

• There was no measureable change to the DS values of any loop on the other two feeder cables.

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Step 4 – introduce new firmware

• QTC released firmware V 3.53 to deal with the DS issues.

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Step 4 – introduce new firmware

• QTC released V 3.53 specifically to deal with the issues we had identified.

• There were MARGINAL improvements

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Step 5 – Swap detector boards

• Did the high DS values move with the detector boards or remain with the loop?

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Step 5 – Swap detector boards

• Did the high DS values move with the detector boards or remain with the loop?

• They remained with the loop.

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Step 6 – Swap logic rack

• Each QTC logic rack was temporarily replaced with other manufacturers logic racks

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Step 6 – Swap logic rack

• Each QTC logic rack was temporarily replaced with other manufacturers logic racks

• There was NO measureable improvement

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Step 7 – Re-cut loop

During the initial loop condition survey there were no issues detected on any of the detector loops that were recording high DS values.

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Step 7 – Re-cut loop

During the initial loop condition survey there were no issues detected on any of the detector loops that were recording high DS values.

One of the worst performing loops was selected to be re-cut.

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Step 7 – Re-cut loop

One of the worst performing loops was selected to be re-cut.

There was an immediate and significant improvement in DS

values

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Step 7 – Re-cut loop

• One by one each poorly performing loop was replaced.

• There was an immediate and significant improvement in DS

values at 7 out of 10 sites

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Effect of capacitance

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Water and Capacitance

• Since the external capacitance is determined by the dielectric constant of the slot sealing and feeder cable, the loop wire and feeder should be completely sealed to prevent water ingress. The large dielectric constant of water produces a significant change in the external capacitance and causes the apparent loop inductance to change. Thus, unstable loop operation can result.

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Q Factor

• Loop quality factor Q is a measure of the losses in an inductive-loop detector system.

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Q Factor

As a loop deteriorates, the inductance reduces, resistance and/or capacitance increases then the Q factor will reduce. Deteriorationof the loop and lead-in wires reduces Q and eventuallyprevents the system from oscillating even with a known gooddetector.

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Testing Q Factor

• The HILT 9000 is an example of a tool designed to test and measure the parameters of inductive loops used in the Traffic Signals.

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Conclusions

• With the current firmware releases installed there is no discernable

difference in the detector performance between any of the TSC4 controller

models• The current tests used to determine the

quality of the inductive loop and feeder cable do not provide the full picture.

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Thankyou