Hello PSNers -- I "lurk" here as a result of a latent interest in seismology though I am not personally active in the field. I have, however, maintained a long standing professional and personal interest in the field of precision timekeeping. I can appreciate the importance of precision time references to seismology. The seemingly simple requirement of maintaining a precise time reference (clock) leads to a field that can become extremely complex when precision is taken to its limits. For your purposes I can suggest the following (in order of increasing precision): 1. Use your PC clock to time stamp or otherwise mark your plots. PC clocks are notorious for wandering all over the place however. In the absence of regular discipline they can be expected to accumulate errors in the order of 10s of seconds within a few days to a few weeks. There is sometimes discussion that improving the accuracy of the Xtal in the PC will improve the accuracy of the clock. This is doubtful, however, since much of the inaccuracy is traceable to failure of the OS to reliably service the timer interrupts. The accuracy of the PC's clock can probably be improved by regular (say daily) manual adjustments using the radio transmissions of WWV (as an example) as a reference. There are also I/O expansion cards available that carry a high accuracy time base which is often referenced to an oven stabilized (OCXO) or temperature compensated (TCXO) crystal oscillator. These can hook into the system BIOS so that calls for system time will be derived from the add-in reference. 2. The PC clock can also be disciplined in the manner suggested by Mr. Hancock using a program that communicates with the Network Time Protocol (NTP) or SNTP servers maintained by numerous sites throughout the world such as Tick and Tock at the USNO. A particularly nice package for this purpose is 4DTIME which is offered as a freeware package at http://www.thinkman.com This is true "freeware" not a "demo" or "evaluation" version. The only "payment" that Rob requests is an email describing your application and suggestions for improvement. If you are so lucky as to enjoy a full time internet connection such as I do through my cable modem, this software can be set to wake up periodically and do an automatic PC clock up date while running minimized. Using this technique you can probably maintain PC clock accuracy to better than 0.1 second. 3. Next would be using a WWV or WWVB radio time standard receiver. One of my favorites is the old (now obsolete) Heathkit GC-1000 Most Accurate Clock. This is a scanning HF receiver that samples the WWV transmissions on 5, 10, and 15 MHz and decodes the time signals which are used to discipline a local 6 MHz oscillator. I have the optional RS-232 output port installed on mine. This emits the local time base once per second. Using a reasonable antenna so that it gets regular updates, this clock will maintain time accuracy in the order of a few 10s of milliseconds. These things are becomming quite rare, so if you are lucky enough to run across one at a ham radio fest or yard sale, *grab* *it*!!. 4. Finally, through the efforts of Dr. Thomas A. Clark, W3IWI, a well known radio amateur and consummate tinkerer and a number of associates, truly precision GPS based time keeping has been brought to the level of amateurs. Dr. Clark has developed hardware/software solutions which bring the very high precision of the GPS satellite time bases to the common PC. Using his methods, sub-microsecond accuracy time bases become available to the amateur seismologist. Ultimately, time base accuracy in the order of a few 10s of nanoseconds is possible. For further information I suggest that you subscribe to the TAPR (Tuscon Amateur Packet Radio) TACGPS email list. Go to http://www.tapr.org and follow the links to the Special Interest Groups (SIG) mail lists subscription page. Also, visit http://www.synergy-gps.com/ Synergy specializes in marketing the Motorola family of Oncore GPS receiver modules which are great for timekeeping applications. In particular, the Oncore UT+ GPS receiver has been optimized for precision timekeeping purposes and is the one capable of serving up time to a precision of about 10 nanoseconds. 5. If that doesn't keep your seismometer happy, go buy an atomic standard. These occasionally show up on ebay! http://www.ebay.com Good luck and good time, Bob Smith "Robert L. Hancock" wrote: > > I have noticed periodic exchanges on the problems and solutions to > obtaining the correct time for timing and keeping timed a seismograph.. > I plan on building one in the forseeable future, and this along with > other subjects has been of interest to me. Recently, I ran across a > page from the US Naval Observatory, our official timekeeper, about > computer programs that can be downloaded and used to maintain timing > with computers I have installed one on my computer and was surprised at > how much drift there was in my cpu clock. > > http://www.eecis.udel.edu/~ntp/software.html > > The main page for the US Naval Observatory is > > http://www.usno.navy.mil/ > > I am not certain how useful this will be to anyone, but thought I would > mention it as I do remember having seen this source discussed. Most > discussions seemed to be focused on either receiving WWV or a similar > type signal, or using the timing obtained from the GPS satelites. This > site has a large variety of programs utilizing many different operating > systems. Some are shareware and free while others require registration > and $. > > Hopefully this will help someone.......... > > Cheers, > > Bob Hancock > Randolph, NJ > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. -- --------- Avoid computer viruses -- Practice safe hex ------------- * * Specializing in small, cost effective embedded control systems * * Robert L. (Bob) Smith Smith Machine Works, Inc. internet bobsmith5@.............. Lumlay Road landline 804/745-1065 Richmond, Virginia 23236+1004 __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>