They Can Spell the Success or Failure of Revenue Control
January, 2009Tom Potter, President of Reno A&E and the designer of the first commercially successful digital solid-state self-tuning loop vehicle detector, spoke with PT last month, focusing on this crucial but often overlooked piece of your PARCS. Editor.
"An inductive loop vehicle detector is a metal detector,” said Tom Potter. “It works on the same principle as portable metal detectors seen at beaches and other locations where people use them in hopes of finding lost coins, jewelry or other valuables in the sand.
“Treasure hunters move the search coil above the surface of the sand, and when a disturbance occurs in the coil’s electrical field, the electronic circuitry responds and alerts the user that a buried metal object exists near the search coil.
“Portable metal detectors and inductive loop vehicle detectors operate on the same principle. In an inductive loop detector, a stationary coil is looking for moving objects, namely vehicles. The location and size of the inductive loop are determined by the detection requirements of the control system.
“For example, in parking systems, reliable vehicle detection information is needed to properly control traffic using devices such as gates, gate arms, barriers, etc. In addition, there is a valuable benefit in obtaining highly accurate vehicle count information. Accurate count information can be used to increase revenue, direct drivers to available parking spaces, etc.
“Early loop detector designs were roughly equivalent to black-and-white TV sets with mechanical tuners. You may recall adjusting ‘rabbit ears’ trying to improve ‘snowy pictures.’ You also may recall adjusting inductive loop detectors, trying to achieve minimum acceptable operation.
“Today’s loop detector technology is much closer to that of high-resolution digital flat-panel color TV sets. Today’s technology offers full self-tuning for all loop configurations, plus continuous compensation for environmental changes such as temperature and moisture.
“To achieve a highly accurate and reliable vehicle detection system, you must understand the importance of selecting the proper material for the inductive loop and the best available electronics,” Potter said.
“The ‘wire loop’ located in the pavement is a very critical part of the detection system. Standard house wire such as THHN absorbs moisture and easily develops leakage paths and shorts to ground.
“Faulty loop wire problems and electrical connections are the most common sources of loop detector problems. Changing electronics does not repair faulty wire insulation and/or poor connections. Saving pennies on loop wire results in unreliable detector performance and unhappy customers!!!
“I highly recommend the use of ‘preformed loops,’ manufactured in a controlled environment using correct materials, procedures and tools,” Potter said. “Complete quality control during the manufacturing process is essential.
“The best installation procedure is to locate the loops in the proper area and then pour the concrete over them. If that’s not possible, they should be cut into concrete – loops cut into asphalt can be problematic.
“As vehicles pass over the asphalt, it moves, particularly during acceleration and braking in hot summer weather. The moving aggregate in the pavement cuts into the loop insulation. The softer the insulation, the sooner loop insulation failures occur. Preformed loops with tough high-temperature insulation have proven to survive very harsh environments,” Potter said. “There is no substitute for proper loop wire insulation.
“The problem is that if a loop fails at a traffic signal, the ability to move traffic is compromised, which results in delays and congestion. In a parking garage, a gate may not close, or worse, may close at the wrong time.
“We can do some pretty amazing things with the electronics, such as detecting tailgating and differentiating between cars, motorcycles, trash cans and steel-toed shoes, but if the loop itself fails due to poor material and installation, all the sophistication in the world is useless.”
Potter noted that detectors in parking garages are used to close gates after a car exits and to prevent gates from closing when a vehicle is present. They also are used to “arm” ticket dispensers so tickets cannot be issued unless a vehicle is present, as well as to “arm” card readers so a vehicle must be present before a card is read. “This prevents cards from having their ‘passback’ mode reset and allowing more than one vehicle to exit with the same permit,” Potter said.
“More complex installations use detectors to ensure that vehicles are traveling in the correct direction in lanes (more than one loop is needed for this purpose), and to ensure that the transaction is complete before making a ticket valid or resetting a passback mode.
“In this last case, an online system will issue a ticket when a car is present, but the ticket will not be valid if the car does not complete the process by entering the garage. The vehicle must exit the loop at the dispenser and then exit the closing loop at the gate. This process could be critical in preventing improper issuance of tickets at airports, for instance, where new tickets can be swapped for those of long-term vehicles. In this case, considerable revenue can be lost,” Potter said.
“In multilevel parking facilities, vehicle detectors can be used for counting, feeding information back to the central office and for driving floor displays informing drivers where space is available. In stadium parking situations where lanes are periodically used, it is recommended that the loops be permanently installed in the normal manner, and that the electronics be housed in a box nearby where they can be unplugged and stored securely when not in use,” Potter said.
Want to find out if your dispenser loop is working? Walk up to the dispenser and push the button. If a ticket is issued, you have a vehicle detection failure. This is crucial to the revenue controls in your facility. Unfortunately, he said, a test at a gate usually occurs when the gate stays open after a car leaves, or worse, closes on a vehicle.
“I know some manufacturers of revenue control systems are of two minds concerning having loop detectors integrated into the gate controller electronics,” Potter said. “My feeling is that if loop detectors and controller electronics are independent, the end user has total flexibility in separately choosing operational features for each piece of equipment. This flexibility increases system value.
“If a repair or upgrade is needed, separate components can be removed and replaced without needing to replace an entire system. Also, due to the cost of a single integrated system, a spare may not be readily available for maintenance requirements.
“Retaining flexibility is something to consider when making the final decision on selecting equipment,” Potter said.
Tom Potter can be reached at firstname.lastname@example.org.