Inductive Loop Detector

Transcription

1 Naztec Operations Manual For Inductive Loop Detector Model 722TXC TS1/TS2 April 2003 Published by: Naztec, Inc. 820 Park Two Drive Sugar Land, Texas Phone: (281) Fax: (281) Copyright 2003 Naztec, Inc. All rights reserved.

2 Table of Contents 1. General Description User Interface and Settings Sensitivity Selection Frequency Selection Pulse/Presence Selection Option Selection Extend Timing Selection ( T Option) Delay Timing Selection ( T Option) Re-tune Timeout Selection ( X Option) Detect LEDs Fault LEDs Reset Button Configuring TS1/TS2 Operation Installation Instructions Selecting the Sensitivity Field Troubleshooting Loop Inspection Theory of Operation General Concept Loop Oscillator Gate Array Counter Micro-Controller Specifications Electrical Specifications Operational Specifications Pin Assignments Naztec, Inc. 1

3 1. General Description The Naztec 722TXC is an advanced two-channel micro-controlled digital inductive loop detector. The 722TXC and its derivatives employ state-of-the-art gate array and microcontroller design. The detector meets or exceeds the NEMA requirements for a 222-style detector. Naztec s 722TXC provides front panel selectable sensitivity, pulse/presence, and frequency settings. There are 15 sensitivity settings available that range from 1.25% to 0.006%. One sensitivity setting also allows for disabling a channel completely. Two frequency switches are available, allowing a total of four user-selectable frequencies per channel. The pulse/presence setting permits the user to select the detector output mode. Pulse mode will produce a single 125 ms pulsed output each time a car enters the loop, while presence mode will produce a constant output while a car is in the loop. The detector s use of high-speed gate array logic permits far quicker detector response time than conventional scanning detector design. Six of the fifteen available sensitivity settings allow for response in less than 2ms. Never does a response time exceed 30ms. The 722TXC sequentially scans each loop channel. This technique eliminates crosstalk between channels on the same detector, reduces crosstalk between channels on adjacent detectors, and reduces loop oscillator power consumption by 50%. The detection outputs on the 722TXC are optically isolated to maximize transient protection. The design also allows for the outputs to place a constant call when no power is applied to the detector. The 722TXC provides a highly accurate pulse output for count. Count outputs are available on separate pins. The T option offers standard extend and delay settings. Extend settings are available from 0 to seconds in ¼ second increments. Delay settings are available from 0 to 63 seconds in 1- second increments. If this feature is not included on the detector, then both extend and delay settings are effectively 0 seconds. A retune time may be selected for detectors that have the X option. This time indicates the maximum time that a call will be held before re-tuning the detector. The time may be set from 1 to 15 minutes in 1-minute increments, or set to the default value by selecting 0 minutes. Detectors without this option use the default value of 30 minutes. The C option includes an RS232 link that may be used to retrieve information such as fault status, detection status, loop operating frequency, and other operating parameters. This information can be instrumental in analyzing loop performance or troubleshooting an intersection problem. Naztec, Inc. 2

4 ON ON 2. User Interface and Settings The following section is subdivided into the various featmures available on the 722TXC. Each sub-topic then addresses the details of the particular feature. 2.1 Sensitivity Selection Each channel has four switches associated with its sensitivity setting. The switches are labeled 1,2,4 and 8. They permit 15 different sensitivity settings, and the ability to disable a channel. Each channel automatically re-tunes when the sensitivity is changed. Re-tuning caused by a setting change is equivalent to a re-tune caused by a reset -- the channel s associated fault indicators are cleared and the channel operates at the new setting. The following picture and table illustrate sensitivity selection: OPTION P/PR FREQ SENSE O P A B Setting Sense Resp. Time 0 OFF R R R R N/A % R R R L 1.60 ms % R R L R 1.60 ms % R R L L 1.60 ms % R L R R 1.60 ms % R L R L 1.62 ms % R L L R 2.00 ms % R L L L 2.60 ms % L R R R 3.50 ms % L R R L 5.00 ms % L R L R 7.25 ms % L R L L 11.0 ms % L L R R 12.7 ms % L L R L 14.3 ms % L L L R 21.0 ms % L L L L 26.0 ms 2.2 Frequency Selection Each channel has two switches associated with its frequency setting. The switches are labeled A and B. They permit the user to modify the operating frequency of the loop to reduce crosstalk between adjacent detectors. OPTION P/PR FREQ SENSE O P A B Setting Frequency A B 0 Lowest R R 1 Low R L 2 High L R 3 Highest L L Naztec, Inc. 3

5 ON ON 2.3 Pulse/Presence Selection Each channel has one switch associated with its pulse/presence setting. The switch is labeled P/PR. Moving the switch changes the operation of the detector immediately. In presence mode, the detection output is held active while a car is present on the loop. In pulse mode, the detection output is pulsed active for 125ms when a car enters the loop. The output is pulsed again for each subsequent car regardless of how many may already be sitting on the loop. The detector s regular detection output may be used for counting when the detector is in pulse mode. OPTION P/PR FREQ SENSE O P A B Setting Presense Pulse P R L 2.4 Option Selection The option switch is reserved for use on loop detectors that have custom software. Unless explicitly instructed by a manual addendum, this switch must ALWAYS be in the OFF (Right most) position. OPTION P/PR FREQ SENSE O P A B Setting Option O R 2.5 Extend Timing Selection ( T Option) Each channel has six switches associated with its extend setting. These switches are not available via the front panel. The card must be removed from the slot for access to the switches. Extend timing is only available in presence mode. Extend timing determines the length of time that the detection output will be held active after the vehicle has left the loop. This setting is available from 0 to seconds in ¼ second increments. To arrive at a desired setting, the switches are pushed to the ON state. The values of all the ON switches are then added together to get the total time selected for the extend setting. While an extension is active, the front panel detect LED will flash at a rate of 8Hz. EXT & DLY DELAY EXTEND ON Naztec, Inc. 4

6 2.6 Delay Timing Selection ( T Option) Each channel has six switches associated with its delay setting. These switches are not available via the front panel. The card must be removed from the slot to access the switches. The delay timing is only available in presence mode. It determines the length of time that the detection output will be delayed before providing an active output once a vehicle has entered the loop. This setting is available from 0 to 63 seconds in 1-second increments. To arrive at a desired setting, the switches are pushed to the ON state. The values of all the ON switches are then added together to get the total time selected for the extend setting. While a delay is active, the front panel detect LED will flash at a rate of 2Hz. EXT & DLY DELAY EXTEND ON 2.7 Re-tune Timeout Selection ( X Option) Each channel has four switches associated with its re-tune setting. These switches are not available via the front panel. The card must be removed from the slot for access to the switches. The re-tune timing is only available in presence mode and determines the maximum length of time that a detection output will be held active. This value is selectable from 1 to 15 minutes in 1-minute increments. A setting of 0 minutes will default to 30 minutes. To arrive at a desired setting, the switches are pushed to the ON state. The value of all the ON switches is then added together to get the total time selected for the re-tune setting. RE-TUNE TIMEOUT ON RE-TUNE CH CH2 Naztec, Inc. 5

7 2.8 Detect LEDs Each channel has one detect LED used to indicate a variety of states relating to the detect output. The LED blinks at different rates to indicate to the user its current state. FAULT CHANNEL 1 DETECT Rate Meaning Off No vehicle/channel Off On Vehicle on loop 8 Hz Flash Extend is active 2 Hz Flash Delay is active 2.9 Fault LEDs For each channel, one fault LED is used to indicate the various fault conditions that may occur. The fault LED indicator latches the last fault that occurred. A blinking fault LED does not necessarily indicate that a fault is in progress; instead, it indicates the most recent fault since the detector was last reset. Pressing the reset button will clear the fault indications and reset the entire detector. FAULT CHANNEL 1 DETECT Rate Meaning Off Loop operation/channel Off On CPU Failure 8Hz Flash Loop Shorted 2Hz Flash Loop open 1/2Hz FlashLoop inductance change > 25% 2.10 Reset Button The reset button available on the front panel has the same effect as removing and reconnecting power. Depressing the reset button will clear all indications and force a re-tune on all channels at their selected sensitivity. RESET Naztec, Inc. 6

8 2.11 Configuring TS1/TS2 Operation Each unit has two jumpers that select the operation mode as either TS1 or TS2. J5 J2 Jumper 2 (J2) selects the fault status output mode as either TS1 or TS2. Position Installed Removed Function Operate as TS2 Operate as TS1 Jumper 5 (J5) selects the output pin for channel two fault status. Position Function 1-2 TS2 Standard Pin Out 2-3 TS1 Naztec Standard Pin Out Naztec, Inc. 7

9 3. Installation Instructions The following section addresses issues that arise during installation. The topics cover field troubleshooting, loop inspections, and sensitivity selection 3.1 Selecting the Sensitivity It is very important that the proper sensitivity level be selected to allow the loop detector to operate as desired. If the sensitivity is too low, then the loop detector will miss calls. If the sensitivity is too high, the loop detector will issue false calls. However, it is accepted that if a detector is going to be biased, it is desirable that it be biased toward false calls. Therefore, it is better to have the sensitivity a little too high than too low. The following procedure will help simplify this process. 1. Set the sensitivity setting to 5 2. If all vehicles are being detected, reduce the setting by one 3. If all vehicles are NOT being detected, increase the setting by one 4. Repeat steps 2 or 3 until all vehicles are consistently detected 5. Increase the sensitivity setting by one. 3.2 Field Troubleshooting The following section responds to a few common problems Intermittent Faults Verify good crimps on the loop lead-ins Check that external lightning suppression is not faulty by removing it Tighten loop terminal connections at the loop termination panel in the cabinet Follow loop inspection procedure in section 3.3 to check loop specifications Detector Does Not Operate Verify that 24 VDC is present and within specifications Check that the external reset line is not active (grounded) Make sure channel sensitivities are not set to 0, thus disabling the channels Detector Is Missing Vehicles Increase sensitivity by one until the detector sees all vehicles Detector Is Generating False Calls Decrease sensitivity by one until the false calls cease Naztec, Inc. 8

10 3.3 Loop Inspection Many times poor loop detector operation can be attributed to poor loop condition or installation. The following is a very brief checklist that will allow the user to quickly inspect the loop. This test is not extensive; therefore a loop that passes this test does not indicate that it is necessarily free of faults or within specification. It is suggested that each loop lead-in be a twisted pair with shielding termination at the cabinet chassis ground. 1. Disconnect the loop inputs from the cabinet 2. Meg the input to earth ground; they should be greater than 1 MegaOhm 3. Disconnect the loop shield from the cabinet ground 4. Meg the shield to earth ground; they should be greater than 1 MegaOhm 5. Use a multi-meter to measure the resistance of each loop; they should be less than 4 Ohms. Naztec, Inc. 9

11 4. Theory of Operation The following section discusses the 722TXC theory of operation in a modular fashion. The detector is broken down into each major operational block. 4.1 General Concept The basic operation of a loop detector is to monitor the resonant frequency of an inductor (the loop) and a capacitor pair. When a metallic body passes over the loop, a shift in the resonant frequency occurs relative to the change in inductance caused by the vehicle passing over the loop. The sensitivity simply identifies a threshold that must be passed due to the proportional change in order for a detect output to be activated. Simply stated, a loop detector monitors for a vehicle by waiting for a pre-described frequency change to occur due to the passing vehicle. 4.2 Loop Oscillator The basic components of the loop oscillator consist of an op-amp comparator, an inductor (the loop) capacitor pair, some feedback resistors, and control lines. The inductor (the loop) is coupled to the circuit via an isolation transformer. The purpose of the transformer, as its name suggests, is to electrically separate the oscillator circuitry from the loop in the street. This contributes to the circuitry by dampening the effects of static discharges, and permits lower grade loops to operate properly. The transformer is paralleled with a capacitor to form a tank circuit. A tank circuit oscillates at a resonant frequency when excited by a voltage source. The op-amp comparator provides the excitation source, and via positive feedback resistors, it is the crucial component in sustaining excitation at the resonant frequency, and squaring up the output so it can be seen as a digital signal. Each oscillator circuit has control lines that initiate or stop its operation. 4.3 Gate Array Counter The gate array counter enables the use of a high frequency source for the count basis. The squared up output from the oscillator is fed into the gate array. The gate array circuitry then establishes a high-resolution measurement of the amount of time that has passed between a preset number of oscillations. If a frequency difference occurs in the oscillator, it is seen as a change in the measurement time in the gate array. This information is then made available to the micro-controller. 4.4 Micro-Controller The micro-controller is the brains of the detector. It is responsible for coordinating the operation of the gate array counter and the loop oscillators. The micro-controller is also responsible for reading the user switches and determining the sensitivity, delay, extend, and retune setting that the user requested. Based upon that information, the micro-controller is able to control the loop oscillators in order to operate them in a manner that will provide the information desired. Once a detection is established, the micro-controller will modify its output signal based upon the delay and extend settings. Naztec, Inc. 10

12 5. Specifications 5.1 Electrical Specifications The following information provides a detailed set of electrical characteristics of the 722TXC Input Power Supply: 12/24 VDC +/- 25% 100ma MAX (50ma per channel) Reverse Polarity Protection Oscillator Voltage: 8 VDC +/- 5% Logic Voltage 5 VDC +/- 5% Input Transients: Transient Pulse Width: +/ Ohms +/ Ohms 10 µsec 5.2 Operational Specifications Self-Tuning: Temperature Tracking: Loop Inductance Range: Loop Frequency Range: Sequential Scanning: The detector is tuned and fully functional within one second after power up for most settings. Higher sensitivities may require more time. The detector automatically compensates for frequency shifts due to changes in temperature. 20uH to 2000uH 10 KHz to 80 KHz The loops are energized alternately to eliminate cross-talk on a single card, and reduce it on a system wide scale. 5.3 Pin Assignments The following table details the card-edge connector pin assignments: J1 Card Edge Connector PIN A- DC Gnd PIN 1- Inhibit 1 PIN B- DC Gnd PIN 2- Inhibit 2 PIN C- Ext Reset PIN 3- Addr 3 PIN D- Loop 1A PIN 4- Loop 1A PIN E- Loop 1B PIN 5- Loop 1B PIN F- CH1(+) PIN 6- Addr 0 PIN H- CH1(-) PIN 7- Status 1 PIN J- Loop 2A PIN 8- Loop 2A PIN K- Loop 2B PIN 9- Loop 2B PIN L- Earth Gnd PIN 10- Addr1 PIN S- Count 1 PIN 15- Addr 2 PIN W- CH2(+) PIN 19- TXD PIN X- CH2(-) PIN 21- RXD PIN Y- Count 2 PIN 22- Status 2 Naztec, Inc. 11