NEW ZEALAND AND
AUSTRALIA TIME RESOURCES
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WHAT TIME FORMAT AND ACCURACY
DO YOU NEED ?
CONSIDER YOUR REQUIREMENTS:
- We assume that you have no problem working out the hour and
minute. This web site is concerned with getting the right second and
fraction thereof.
- Many people in homes and offices are quite happy with an accuracy
of "a few seconds" or "about one second". For this you can use radio
time pips on the hour, most handheld navigation type GPS receivers, some telephone
services, and setting the computer clock from an Internet NTP server. In
some other regions of the world, 'radio controlled' (so called 'Atomic') clocks
are often used.
- But for visual, manual scientific observations a time reference
accurate to 0.1 second (100 ms) is generally required. In some cases
(ref. below), the telephone 'speaking clock' may just be good enough for
some tasks. However, shortwave radio or a dedicated GPS time receiver
(i.e. not a standard navigation GPS) may be a better option.
- For instrumental timing (video or photometer), we really need 10
ms or 1 ms or better. The most practical option here is a GPS device
with a dedicated time function that uses
the 1PPS time output (i.e. not an average standard navigation GPS).
- (** For the connoisseurs amongst our readers we shall not enter here
the discussion over the definitions of, and differences between 'accuracy',
'inaccuracy', 'precision', 'uncertainty'...... that would be a whole separate
book.....)
- How will an observed "Event"
be related to a "Standard Time" system? Where and
in which directions are known 'delays'.
- Do you need a time reference for a "Single Spot Check"? Such as 'setting'
a stopwatch or observing one single well defined event? At a 'set'
time, or at a time of your choosing?
- Or do you need a recordable "Continuous Time Stream for ~ many minutes or longer?
For example for an asteroidal occultation or a grazing lunar occultation?
- For Video recording the best, and now readily available,
option is a GPS based Video Time
Inserter
FOR SERIOUS WORK:
SOURCES OF
TIME - Direct Links to a Primary Time Standard:
- GPS - using the dedicated 1 PPS
time output - EXCELLENT
- for accuracy and availability, GPS is the superior option, but
Dedicated GPS Time devices are required for high accuracy.
(Caution: NOTE that the time display on standard handheld
'navigation' GPS units is often a few seconds off).
- Short Wave Radio Standard Time Stations - GOOD - depending on reception,
these stations offer very decent accuracy and good reliability
- WWVH, WWV, CHU, etc. Very good if you can elect to perform
your time check at a time of the day with good SW radio propagation.
- Setting the Computer clock - possible, with 'fair' accuracy depending
on the method and hardware used and the type of computer link available.
Not always as easy as you may think.....
- Low Frequency self correcting clocks
- generally these are not expected to work reliably in
the New Zealand / Australian region for lack of a local transmitter.
- Telephone (fixed line, GSM,
CDMA, 3G) - usable, please refer to the linked
page for specific considerations of accuracy, depending on th primary
source of time used for each available number and the transmission mode
(fixed line or mobile / 'cell' ).
- Regular FM / MW Broadcast
Radio - usable in some cases of well specified
time pips on the full hour. Increasing concerns over changes in
time source used, networking arrangements and current and/or future accuracy
levels.
To carry 'time' between a device linked to the primary source and e.g.
a remote field site, or a group of multiple observing stations, or to
maintain local time when the primary source is inaccessible, we may also
use a (secondary) Local Clock
like a clock, stopwatch or electronic
bleeper, which is first synchronised with a primary time source and checked again after the observing run.
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