Model 272M Two Channel  Digital Loop  Detector with  Multiplexed  AccuCount™  Output

Features & Benefits

• The AccuCount™ feature enables accurate counting of vehicles entering the loop(s) even when preceding vehicles remain present over the loop(s).  Never before has such count accuracy been possible. 
• AccuCount™ works with various loop configurations.  (See reverse side for specifications.) 
• Multiplexed mode of operation provides count and normal detect on the same standard output pin.  No rewiring is needed! 
• Molex connector on front panel provides a pulse (AccuCount™) output for each channel of detection. 
• The Winky-Blink™ loop monitor remembers and indicates intermittent and failed loops. 
• If intermittent or failed loops self-heal, the detector will resume normal operation without requiring a manual reset. 
• Loops are sequentially scanned and four separate loop frequencies per channel permit complete elimination of crosstalk. 
• DIP switches on front panel for sensitivity, frequency, and output mode selections. 
• Eight levels of sensitivity per channel. 
• Two selectable modes per channel 
         Pulse 
         Presence, long hold time 
• Self-tuning and complete environmental tracking. 
• Complete low power CMOS digital design. 
• Operates on single DC power supply. 
• Transformer isolation of loops. 
• Red, high intensity LED DETECT indicator. 
• Front panel width is 1.12" (2.84 cm). 

Specifications

Self-Tuning: The detector automatically tunes itself and is fully operational within 1 second after being reset.  30 seconds is required before full presence time is possible. 
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Environmental & Drift Tracking:  The detector is fully self-compensating for environmental changes and component drift over the full temperature range and the entire loop inductance range. 
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Loop Inductance Range:  20 to 2500 microhenries with Q factor of 5 or greater. 
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Loop Frequency:  Four frequencies (normally in the range of 20 to 50 kilohertz) are switch selectable for each channel.  The detector should be manually reset following a manual change in loop frequency. 
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Loop Feeder Length:  Up to 5,000' (1500 m) maximum with proper feeder cable and appropriate loops. 
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Loop Input:  Transformer isolated. 
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Reset:  Switch closure between D.C. Common (Pin A) and the reset line (Pin C) for 2 milliseconds or longer will reset both detector channels.  The detector will not reset when the reset line is held low for 100 microseconds.  Note:  The detector can be manually reset by removing power momentarily, changing the sensitivity switch, or by changing the Mode switch. 
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Grounded Loop Operation:  The loop isolation transformer allows operation with poor quality loops (which may include one short to ground at a single point). 
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Lightning Protection:  The detector can tolerate, without damage, a 10 microfarad capacitor charged to 2,000 volts being discharged directly into the loop input terminals, or a 10 microfarad capacitor charged to 2,000 volts being discharged between either loop terminal and earth ground. 
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Faulty/Intermittent Loop Monitor:  If the total inductance of the detector input network goes out of the range specified for the detector or suddenly changes more than 25%, the detector will immediately generate a failsafe continuous output (CALL) in either presence mode or pulse mode, and the front panel LED will begin repeating bursts of three blinks, the Winky-Blink™ mode.  This failsafe condition will continue until the inductance returns to its previous value at which time the detector output will automatically resume normal operation.  However, the red Detect LED will continue in the Winky-Blink™ mode until the detector is manually reset or a power interruption occurs.  This feature helps identify intermittent loop problems not present during troubleshooting.  (The detector input network consists of the loop or loops plus the feeder [lead-in or home run] cable up to the connector on the detector). 
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Loop Configurations:  AccuCount™ may be configured to work with different loop configurations by on-board DIP switches. 
    One diamond or large rectangular loop. 
    One 6' x 6' loop (1.83 x 1.83 m), 6' (1.83 m) diameter round, or a Quadrupole™ loop of any size. 
    Two 6' x 6' (1.83 x 1.83 m) loops in series. 
    Four 6' x 6' (1.83 x 1.83 m) loops in series. 
Note:  For optimum count efficiency, 9' (2.74 m) spacing is recommended for loops wired in series. 
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Sequential Scanning:  The two loops are activated alternately to minimize crosstalk. 
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Sensitivity (Under Construction): Vehicle detection results from a sufficient negative change in loop inductance (-delta L/L).  Seven detection sensitivity levels, plus OFF, are switch selectable per channel.  (Note that the detector is reset automatically whenever the sensitivity level is changed). 

Channel Off State:  While the channel sensitivity switch is set to the DISABLE position, the channel output is off and the channel is reset. 
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Multiplex Outputs:  Switches the output (pin F - CH 1; pin W - CH2) between vehicle detect and count.  The output shall be the count function when the reset line is low (25-500 microseconds) and the output shall be vehicle detect (presence or pulse, as selected) when the reset line is high (25-500 microseconds).  When the reset line is held continuously high, the output shall be vehicle detect only.

Mode Switch Output Functions (Under Construction):  Two modes DIP switch selectable. 

Multiplexed Output Functions:  The multiplexed output is controlled by the reset line.  (See Operators Manual) 

• PRES (Presence) - A precise mode with a hold time of 4 minutes minimum (regardless of vehicle size) and typically 60 to 90 minutes for a car. 
• PUL (Pulse):  A Pulse mode with a pulse of 125±25 ms. duration generated for each vehicle detected.  Each detected vehicle is instantly tuned out if it remains in the loop detection zone longer than 2 seconds.  This enables detection of subsequent vehicles entering the detection zone.  As each vehicle leaves the detection zone, the detector resumes full sensitivity within 0.75 seconds. 
• COUNT (AccuCount™):  A pulse mode with a pulse of 125±25 ms. duration generated for each individual vehicle on the loop matrix.  This AccuCount™ pulse output provides accurate counts of vehicles entering the loop matrix even when preceding vehicles remain present over the loop.  Count output provides a simple pulse output when the mode switch is set to PUL, giving one pulse for each sustained occupancy. 

Auxiliary Outputs:  A front panel Molex connector provides continuous, unmultiplexed count outputs.  For specifications, see previous paragraph. 
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Detect Indicator:  High intensity red light emitting diode (LED) indicates output status of channel: 

• NORMAL CALL:  Indicator is steadily on while a vehicle is still being detected. 
• FAILED OR OUT-OF-RANGE LOOP:  Indicator emits the Winky-Blink™ signal of three 50 ms blinks 50 ms apart once per second. 

Note:  If the loop frequency is manually changed, the Winky-Blink™ signal may appear if the detector is not then manually reset. 
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Response Timing (Under Construction):

Solid State Output Ratings:  A separate open-drain FET solid state output, with source connected to D.C. Common (Pin A), is provided for each channel and the AccuCount™ outputs.  A 47 Volt zener diode is connected across the source and drain for transient protection. 
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Power: 16 to 30 VDC, 80 ma maximum.
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Operating Temperature:  -40° F to +180° F,  (-40° C to +82° C) 
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Size:  4.5" H x 6.875" D x 1.12" W,  (11.43 x 17.462 x 2.844 cm).

Edge card connected is centered on the 4.5" edge. 
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Weight:  6 oz. (172 g) 
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Connector/Pin Assignments (Under Construction):  3-Pin Molex 03-06-1022 front panel connector for AccuCount™ outputs for each channel.  (1272M  harness provided). 

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