[time-nuts] Telecom Solutions DCD Cesium

Magnus Danielson cfmd at bredband.net
Sun Mar 19 08:09:00 EST 2006

From: "Robert Lutwak" <Lutwak at Alum.mit.edu>
Subject: Re: [time-nuts] Telecom Solutions DCD Cesium
Date: Sun, 19 Mar 2006 07:34:43 -0500
Message-ID: <000d01c64b51$807d0930$6400a8c0 at lutwakhome>

Hi Robert,

> Monitor3 will periodically poll and save the status data to disk for you. 
> See the File->Unit Monitoring Panel.  It also has some very cool 
> plotting/analysis features (try View->Plot).  You can learn a lot about your 
> unit by watching the dynamics of the boot sequence.  Grab the data to disk 
> with Monitor3 and go back and look at the plots.

Yes, I have alot of fancy data comming out of it thanks to Monitor3 ;O)

> The old modules were 5045, which was later renamed 4201A.  Some of the last 
> modules (maybe >2004) were named 4201B and had a new CsIII-based servo 
> board.  Also, if you get a 4201A serviced, depending on the failure, they 
> may upgrade the servo to a 4201B servo board.  Monitor3 can tell them apart. 
> Also the servo boards have different part numbers and the new one (4201B) 
> has a big Xilinx CPLD hanging off the microprocessor.

OK. I've got a 4201A, which is logical considering when it was manufactured.

> I'm not sure how much of Monitor3 will work with your older unit.  I wrote 
> it to work with the new CsIII-based units and later went back and cobbled in 
> support for the old 5045/4201A instruments for the guys in technical 
> service.

It seems to make sense (to the best of my knowledge, which I grant is limited
so far).

However, the log feature does not work. Maybe that is one of the differing

> The telemetry was originally designed to work with a dedicated 
> stand-alone Sercel terminal (which has been obsolete for at least 15 years). 
> The old Monitor program (which you may be able to find out there somewhere 
> in cyberspace) only ran in a terminal emulator which only ran on native DOS 
> machines, i.e. it wouldn't run in a DOS window under Windows, because it did 
> low-level serial port control.

Well, looking at the format as I read it in the 4065 manual, I should have no
major problem writing myself a little program and parse it properly to work on
my Linux system. I don't have a Windows box except my (well, actually my
employers) laptop which I for obvious can't lock up for my time/frequency rig
at home.

> I think Monitor3's serial port control functions should work with your 5045, 
> so if you get tired of 2400 baud, you should be able to crank it up to 9600 
> from the System->RS232 menu.

Ah, I'll attempt that! ;O)

> In order to get the 03 alarm, you must have made it through all of the 
> earlier boot sequence, so you must have plenty of signal level, good 
> microwaves, etc.

That sounds re-assuring. Yes, I have assumed this too. It has acheived lock for
some shorter times.

> Without more information I would guess that your unit 
> either:
> a)  Problem in C-field control circuit such that DAC is demanding more 
> current but atoms don't seem to respond.
> b)  Short in one (or more) of the coils inside the tube so that current 
> control gets to limit without locking
> c)  Tube has become magnetized so the Zeeman line asymmetry is big enough 
> that it tries to lock on the wrong peak.


> Watch the "Zeeman Signal Level" during boot (before it throws the alarm). 
> It should be about the same as the "Clock Signal Level."  If it's much lower 
> (in the neighborhood of zero), than you've got no C-Field in the tube, 
> either the supply is failed or the coils are shorted out (badly).

The C-field current starts of at 18 ma when it locks, then it kicks in the 05
alarm, starts regulating and finally the 03 alarm kicks in.

> If you have Zeeman Signal, next watch the "Zeeman Rabi Innovation" during 
> boot.  After the clock's done initializing the clock and gain servos, it'll 
> try to acquire lock on Rabi Zeeman.  You should see this number start 
> relatively high (maybe a couple of hundred either +/-) and then you should 
> see the "C-field current" and the "current-control voltage" change as Zeeman 
> Rabi is driven to zero.  If this succeeds, than all of your electronics (and 
> most of your tube) is working fine.


> Once it acquires lock on Zeeman Rabi, it'll try to hone in on "Zeeman 
> Ramsey."  You'll see the Zeeman Ramsey error suddenly appear (at probably 
> +/- 500 or so).  Then the C-field current will keep changing to try to drive 
> this one to zero.  If all is well, this is the final step of lock.  If the 
> tube is magnetized, enough that you try to lock to the wrong Zeeman Ramsey 
> peak, you will see the Zeeman Rabi Innovation start to creep back upwards as 
> you hone in on (the wrong) Zeeman Ramsey.  In this state, it will eventually 
> kick out an 03 alarm, and possibly an 05 as well.  This is typically caused 
> by exposure to high magnetic fields and is fixed by degaussing the tube.

I think this is pretty exactly my problem. So, I need to degaussing the tube
then, how would you recommend me to do that? It seems pretty DIY-capable. ;O)

I will check the boot sequence like you described.

> By the way, we just finished re-writing the manuals for the CsIII and 
> Cs4000.  The new manuals include a new Theory-of-Operation section (by me), 
> which you may find useful.  It's not the same electronics as your 5045, but 
> the physics and the CBT are the same.  You can get the manuals off the symm 
> WWW site.

Great to hear. I just pulled the 4065, CsIII and Cs4000 manuals so I got that
description. The one thing I missed in the 4065 manual was the description of
which alarms kick in when (so the mapping described problem <-> alarm was not
obvious). It is clearer with the CsIII manual.


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