GTT Canoga C924 Series, Руководство по установке

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Canoga™ Vehicle Detectors
Canoga™ C924X Series Installation Manual
72 – Product Description & Specification
of 4,294,967,295 ticks of 50 milliseconds duration. After 2485 days, 12 hours, 19 minutes and 24.8
seconds without a power failure to the real-time clock, (about 6 years and 9.7 months), this counter
will roll over to zero. If Historical Traffic Data is read during the bin interval immediately after
rollover, there will be an apparent time discontinuity that the system reading the data must handle.
The real-time clock is not affected by unit resets or temporary loss of power with duration of 24 hours
or less. If power loss (power to vehicle detector is removed) is greater than 24 hours (until super
capacitor is discharged), the real-time clock setting reverts to midnight on January 1, 2000. NOTE:
Under ideal situations, it may take weeks for the real-time clock to deplete the super capacitor after
traffic monitoring card power is removed.
The described method of assigning an absolute time to tick-stamped events using data reading system
clock rather than the vehicle detector clock can cause event times to vary slightly between any two
successive reads of Historical Traffic Data. For instance, if there is any drift between the detector
clock and the data reading system clock between successive reads, tick stamped events will be
assigned a slightly different absolute time at the second read as compared to the first read.
To avoid event time discrepancies, the data reading system may reference all relative times to the
vehicle detector real-time clock rather than referencing relative times to the data reading system
clock. Use the following procedure to accomplish this.
Prior to starting historical traffic data binning, set the vehicle detector real-time clock to the data
reading system date and time by using the q5 command. It is preferred that the data reading system
clock be synchronized to NIST time. (This and all other unit commands are detailed in the Canoga
Series C400/C800/C900E/C900/940E/940 Serial Communication Protocol. It may be requested from
GTT at the address or telephone number shown on the back cover of this document.) Then turn power
to the card OFF and then ON. This will update Current Time. From this point on, the data reading
system can read Current Time using the 5 command and then read the traffic monitoring card real-
time clock using the q4 command. The data reading system can then equate, with a small time error
magnitude of the time between command replies, Current Time to the absolute time in the card’s
real-time clock.
The data reading system can use the q4 and q5 commands to keep real-time clocks closely
synchronized. Current time will be “revised” only when there is loss of power to the traffic monitoring
card unit.
8.2.21 Delay and Extension
Canoga C924X vehicle detectors have Delay and Extension timing functions.
Delay timing inhibits the detector output for a period of time after detection. You can select the
Delay Time in 1-second increments up to 31 seconds.
Extension timing extends the detector output for a period of time after the detection is over. You can
select the
Extension Time in 0.25-second increments up to 7.75 seconds.
8.2.22 Sensitivity and Mode Selection
Select the lowest sensitivity setting that will reliably detect all vehicles of interest in the weakest area
of the sensing zone. For example, the center of a loop when loops are used, or the vehicle near lane
division strip when Microloop sensors are used. Lower sensitivity settings present less exposure to
environmental noise, allow faster response, and reduce susceptibility to adjacent lane vehicle
detection.
For either type of sensor, it is very rare that sensitivity setting other than
2 (256 nanohenries), 3
(128 nanohenries) or 4 (64 nanohenries) is appropriate. A good initial setting is sensitivity 3.