Time drift

[pvelez]

I'm doing a T Point run. Its been chugging along for about 90 minutes. Earlier I noticed that the time on PC seemed out so I reset it via the internet.

Looking at it now - it seems to have drifted by about 20 minutes! My pc clock reports its 10.30pm even though its only 10.08.

How does that happen??

Pete

[vignesh1230]

Im guessing the CMOS Battery in your computer.

This is the most likely scenario, especially if your computer is not brand new.
The CMOS battery sits on your computer’s motherboard and provides power to the Complementary Metal Oxide Semiconductor (CMOS) chip. The CMOS chip stores information about the system configuration, including the date and time. The CMOS battery makes sure the chip can store this data even while the computer is turned off and not hooked up to power. If the battery goes bad, the chip starts losing information and one of the symptoms is that your computer no longer maintains its time and date.


Try changing the battery if it keeps happening.

[pvelez]

Thanks Vignesh

would that also happen if the clock is gaining time?

I'm using a FitPC-2 which is super compact. It seems to change the battery I need to unsolder it and solder in a new one - a real pain.

Pete

[Colin_Fraser]

You will have more trouble than a slow of fast clock if the battery was at fault.
I would suggest the Windows Time Service is being stopped. Make your way to services.msc stop the Windows Time Service then start it again.
Make sure you have no trojan turning it off.
Hope it helps...

[pvelez]

Thanks Colin

I've searched the FitPC support site and it seems this issue has popped up for a few other users in the last 12 months. Might be a BIOS thing or something else.

Just downloaded ClockMon which is keeping the clock accurate to within 5 seconds over 20 minutes now so that seems to be doing the trick.

Its odd - the system clock is fast not slow.

I might try your suggestion anyway and see what happens

Pete

[RickS]

[Damn... I see there was another reply in the meantime!]

Pete,

The CMOS battery only maintains the real time clock when the computer is powered off. The typical symptom of a flat battery is the computer losing the date and time when you power it down. A flat battery won't make your clock run slow (or fast) while the computer is up and running.

As to what is making your clock run fast, that's a bit of a mystery to me. Are you or your computer moving at relativistic speeds? :D Could be rogue time synchronization software if you're running any (third party or the Windows Time Service). Have you ever seen it happen before?

I use Dimension4 to keep my Windows clock accurate and it seems to work well:
http://www.thinkman.com/dimension4/default.htm

Cheers,
Rick.

[mithrandir]

Pete, the sledgehammer of clock control programs can be found here (http://www.meinbergglobal.com/english/sw/ntp.htm). This is built from the same NTP sources (http://support.ntp.org/bin/view/Main/SoftwareDownloads) used on just about every *nix system, with a Windows GUI front end added.

[pvelez]

Cheers Rick

No, I'm not moving at relativistic speeds - do I look like a shifty neutrino??

I hadn't noticed it before - but I suspect its been happening for a bit. I've been giving myself heartache trying to get a decent TPoint calibration run done and suspect this has been the cause (he says hopefully).

Have posted elsewhere on that issue so won't bore you all with it.

All very odd - might be something nasty in the pc

Pete

[pvelez]

PS I'd hate to see what this has done to my variable star observations!

Pete

[frolinmod]

+1

That's what I do. Works great with an internet connection. My system time is kept within miliseconds of UTC this way.

In the field when I don't have an internet connection, I connect a GPS with 1PPS output and synchronize to that. My system time is kept within microseconds of UTC this way, which is better than synchronizing to internet time servers.

[pvelez]

Thanks everyone for your responses.

I might investigate GPS as well as the Meinberg program

What is clear is that its the System clock in XP that is playing about not the BIOS based clock. All very odd

Pete

[mithrandir]

Pete,

If you choose to run NTP, I suggest you use these lines for finding servers (note they are "pool" not "server" lines):

pool 0.au.pool.ntp.org. iburst
pool 1.au.pool.ntp.org. iburst
pool 2.au.pool.ntp.org. iburst
pool 3.au.pool.ntp.org. iburst

or a subset of them. You will have to edit the ntp.conf file (can be done as part of the setup) because the installer uses "server" lines.

Which servers you get will change from time to time, but you don't have to worry about servers vanishing or blocking you as these people have volunteered their clocks

[Tandum]

If your clock is drifting 20minutes in 90 minutes it won't matter which online clock you use, there is either something wrong with the PC or something is altering the clock. It's not the battery,that is only used for power loss. Does the clock drift with the pc running at idle?

I'd have to admit I've never had to deal with a pc with a very fast clock before?

[pvelez]

Ok - an update of sorts.

I've run a full virus scan and can find nothing problematic.

Without running ClockMon, my clock is gaining about 20 - 25 seconds per minute. With it on, it resets every minute or so. I think the reset process involves it temporarily slowing the clock rather than simply setting it back. The result is that it runs at varying speeds if monitored by ClockMon.

Leaving the PC off for a few hours and turning it back on, the time is right when it starts but then careers out of control. So I don't think its the CMOS battery.

Linking to the web or a GPS won't help much unless it syncs every few seconds which I don't think it does.

I can manage for now - with ClockMon and guiding, I should be ok to image. But to do some photometry on short subs eg 1 - 2 minutes, I have a problem as the mount is moving at the rate that the system clock dictates not within its own timeframe - so I get smeared stars.

So - any other ideas (besides dumping the wretched pc - which is pretty tempting at the moment)?

Pete

[Colin_Fraser]

The CMOS battery keeps all the settings like PCI configuration, memory size, drive controllers, USB setup and a host of other stuff. It does a whole lot more than just keep the clock ticking. The CMOS battery is okay.
Maybe try to boot the computer into DOS mode and every now and then issue the TIME/t command. If the time is still messed up, the problem looks to be the RTC on the motherboard.
If the time is okay and does not drift at all, then the OS is messing the clock up, in which case an upgrade might fix it.

[wasyoungonce]

Can you watch the clock in bios? How does it fare...fast or what.

If ok then it's an OS issue if not ...sounds like a crystal, PLCC chip or temperature compensation system...maybe be a crystal trimming cap?

[pvelez]

Sadly, I run the pc remotely using VNC so I can't access it when it boots up and so can't access the clock.

The fact that the clock is right when the pc fires up but then drifts suggests its right in the bios.

May need to do a clean install - what a pain!

Pete

[wasyoungonce]

Well, even before it is booted it is still running the RTC so if this is ok at boot....yeah does sound like a conflict of software somewhere.

About the strangest thing I've heard of in awhile for sure!

[pvelez]

Good to know that I am breaking new ground!

Pete

[Joshua Bunn]

Running NTP, it can update your computer clock every 10 sec, but i guess that wont fix the real cause.

[naskies]

It probably sounds silly, but accurate timekeeping on a PC is incredibly difficult from a software and hardware point of view (speaking from experience as someone who has programmed everything from assembly code up to interpreted languages on x86).

There are many different clocks - all running at different speeds - inside a typical PC: the BIOS clock everyone is familiar with, internal CPU clocks, sound card clock, network card clock, power management controller clock, and so on. They naturally/physically run at different speeds, but the operating system also has to switch between them due to hardware constraints.

I'd probably try to start by isolating what the likely problem is: disable time updating over the internet, unplug as many external devices as you can (including ethernet/wifi), and boot the computer in safe mode. Don't load any applications and just leave it running.

If the clock still runs wild, then the culprit may be a driver/kernel issue, or something related to core hardware (e.g. ACPI - power management controller).

If the clock happens to be "fixed", then you can figure out what device/application is causing the problem by a process of addition / elimination.

If it's an internal Windows driver issue, here are some pointers to start looking (ACPI issue, MaxAllowedPhaseOffset setting, etc):

http://social.technet.microsoft.com/Forums/en-US/winserverDS/thread/95f0ff92-f080-4a9d-9d37-fbba6fc9324e/

Also - much like how even with autoguiding you still want a mount that has very smooth PE that can be guided out (think of remote time synchronisation as being like autoguiding), you'll probably want to fix the underlying problem otherwise you may introduce new issues. Most timing loops in software is written with the expectation that time runs forward and smoothly - excessively frequent clock corrections will likely cause problems.

Good luck!