Path: utzoo!attcan!uunet!n3dmc!johnl
From: johnl@n3dmc.UU.NET (John Limpert)
Newsgroups: comp.periphs
Subject: Re: precise time for systems?
Message-ID: <460@n3dmc.UU.NET>
Date: 22 Dec 88 18:36:41 GMT
References: <11615@cup.portal.com> <12812@cup.portal.com>
Reply-To: johnl@n3dmc.UUCP (John Limpert)
Distribution: na
Organization: N3DMC, Silver Spring, Maryland
Lines: 29

In article <12812@cup.portal.com> Michael_J_Ward@cup.portal.com writes:
>There was a feature on San Francisco channel 7 last night about PSTI, a
>company which makes a WWV receiver for synchronizing traffic lights and
>also for computer systems.  How many systems would need such precise
>time-stamping? Do they put one one of these on each server, or somewhere
>in the middle of a network? Is anyone using one of these?

Many data acquisition/recording systems need high precision timing systems.
I work with spacecraft telemetry processing systems that typically tag
received data with a millisecond precision time stamp.  There are some
applications that require microsecond precision (Synthetic Aperature Radar).

Typically the timing data is read from a parallel interface that is
connected to a timing distribution system.  You can't put the timing
data through a network without losing alot of precision.

WWV is fine for many systems, but it is inadequate for a high precision
timing system.  We use atomic standards (Hewlett-Packard Cesium Beam)
and a special LORAN receiver as our timing source.

Accurate timing systems are important for situations where independently
recorded data needs to be correlated with small allowances for error.
Some examples are VLBI (very long baseline interferometry), orbit
determination and seismic monitoring.  Time codes are widely used in
music recording studios, TV stations and motion picture production.

-- 
John A. Limpert
UUCP:	johnl@n3dmc.UUCP, johnl@n3dmc.UU.NET, uunet!n3dmc!johnl