NIST WWV, Fort Collins, Colorado
Cesium Atomic Clock
The current time standard for the United States is a cesium atomic frequency standard at the National Institute of Standards and Technology in Boulder, Colorado. In 1967 a standard second was adopted based on the frequency of a transition in the Cs-133 atom:
1 second = 9,192, 631,770 cycles of the standard Cs-133 transition
Prior to 1964 the international standard second had been based upon the orbital period of the Earth, but the cesium clock period was found to be much more stable than the Earth's orbit! The SI unit of time, the second, is now defined by this transition in cesium.
Atomic Clocks
Very accurate clocks can be constructed by locking an electronic oscillator to the frequency of an atomic transition. The frequencies associated with such transitions are so reproducible that the definition of the second is now tied to the frequency associated with a transition in cesium-133:
1 second = 9,192, 631,770 cycles of the standard Cs-133 transition
The two most widely used atomic clocks in recent years have been the cesium beam atomic clock and the rubidium clock. Such clocks have provided the accuracy necessary to test general relativity and to track variations in the frequencies of pulsars. Atomic clocks are integral parts of the Global Positioning System since extreme accuracy in timing is necessary for the triangulation involved.
GPS clocks
Many modern radio clocks use the Global Positioning System to provide more accurate time than can be obtained from these terrestrial radio stations. These GPS clocks combine time estimates from multiple satellite atomic clocks with error estimates maintained by a network of ground stations. Due to effects inherent in radio propagation and ionospheric spread and delay, GPS timing requires averaging of these phenomena over several periods. No GPS receiver directly computes time or frequency, rather they use GPS to discipline an oscillator that may range from a quartz crystal in a low-end navigation receiver, through oven-controlled crystal oscillators (OCXO) in specialized units, to atomic oscillators (rubidium) in some receivers used for synchronization in telecommunications. For this reason, these devices are technically referred to as GPS-disciplined oscillators.
GPS units intended primarily for time measurement as opposed to navigation can be set to assume the antenna position is fixed. In this mode, the device will average its position fixes. After approximately a day of operation, it will know its position to within a few meters. Once it has averaged its position, it can determine accurate time even if it can pick up signals from only one or two satellites. GPS clocks provide the precise time needed for synchrophasor measurement of voltage and current on the commercial power grid to determine the health of the system.
brk said:I *think* part of the problem you're having is just basic understanding of analytics/object classification vs. "rules", and how the system really works and makes decisions. If you email a couple of video clips of scenes/events that you're having problems with to [email protected] I can have one of my techs take a look. I'll also be at ISC West next month, if you want to come by our booth we can chat a bit there as well. I assume you already signed up for one of the free exhibit hall passes, but if not let me know and I can get a free exhibit hall pass.
If Pete's device is still around for $30, that's pretty slick too.
Time does NOT equal time ZONE. NTP knows nothing of your location and how you interpret time in relation to it.pete_c said:Unrelated to OP; noticed that my Grandstream IP HD cams did change time last Saturday; but the Aircam's did not. Both utilize the internal NTP server. Looks to be a bug in the Aircam firmware as it is configured to get the time from the NTP server; but appears to be doing its own thing.
Right, so presumably the firmware presents a selection somewhere to chose your time zone? And perhaps there's also an option to dis/enable daylight savings time? Some devices don't have the ability to alter their use of DST automatically. Mainly because the programming necessary to do it would exceed either the firmware's size or the programmer's ability. This is because not everywhere treats the DST change in the same way. So lots of times the device makers 'give up' and just present a check box or something that allows selecting DST or standard.pete_c said:Its interesting cuz I cannot find a manual time change in the Aircam configuration pages; only an NTP reference. I am running most current firmware.
Time does NOT equal time ZONE. NTP knows nothing of your location and how you interpret time in relation to it.
Right, so presumably the firmware presents a selection somewhere to chose your time zone?
Time zones are FAR messier than people first expect. The tables behind using them are quite a lot more complex than most programmers fully grasp.
Changing clocks and DST rules has a direct economic cost, entailing extra work to support remote meetings, computer applications and the like. For example, a 2007 North American rule change cost an estimated $500 million to $1 billion,and Utah State University economist William F. Shughart II has estimated the lost opportunity cost at around $1.7 billion USD.Although it has been argued that clock shifts correlate with decreased economic effienciency, and that in 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on US stock exchanges,the estimated numbers depend on the methodology and the results have been disputed.
In 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to US DST. In December 2008, the Daylight Saving for South East Queensland political party was officially registered in Queensland, advocating the implementation of a dual-time zone arrangement for Daylight Saving in South East Queensland while the rest of the state maintains standard time. DS4SEQ contested the March 2009 Queensland State election with 32 candidates and received one percent of the state-wide primary vote, equating to around 2.5% across the 32 electorates contested. After a three-year trial, more than 55% of Western Australians voted against DST in 2009, with rural areas strongly opposed. On 14 April 2010, after being approached by the DS4SEQ political party, Queensland Independent member Peter Wellington, introduced the Daylight Saving for South East Queensland Referendum Bill 2010 into Queensland Parliament, calling for a referendum to be held at the next State election on the introduction of daylight saving into South East Queensland under a dual-time zone arrangement.[66] The Bill was defeated in Queensland Parliament on 15 June 2011.
In the UK the Royal Society for the Prevention of Accidents supports a proposal to observe SDST's additional hour year-round, but is opposed in some industries, such as postal workers and farmers, and particularly by those living in the northern regions of the UK.
The syntax is: std offset dst [offset], start [/time], end [/time]
Default is set to: MTZ+6MDT+5,M4.1.0,M11.1.0MTZ+6MDT+5,
This indicates a time zone with 6 hours offset with 1 hour ahead which is U.S central
time. If it is positive (+) if the local time zone is west of the Prime Meridian (A.K.A:
International or Greenwich Meridian) and negative (-) if it is east.
M4.1.0,M11.1.0
The 1st number indicates Month: 1,2,3.., 12 (for Jan, Feb, .., Dec)
The 2nd number indicates the nth iteration of the weekday: (1st Sunday, 3
Tuesday...)
The 3rd number indicates weekday: 0,1,2,..,6( for Sun, Mon, Tues, ... ,Sat)
Therefore, this example is the DST which starts from the first Sunday of April to the
1st Sunday of November