[time-nuts] Re:FTS 5030 cesium frequency standard

Bill Hawkins bill at iaxs.net
Sun Nov 28 18:28:08 EST 2004

There is a good description of Cesium (in a strange setting)
in the FAQ for alt.cesium at:


I suspect that the "oven" is actually more like a vacuum
tube heater, which heats the metal (maybe not pure) until
electrons boil out of the metal. There ought to be a curve
for emission vs. temperature, maybe called the work function.
Also, this info may be under caesium.

The HP 5061 manual tells you the beam current that is required.
If I had no clue about the thermistor, other than that it had
a negative temperature coefficient, I'd assemble the whole
business and put a variable resistor across the thermistor.
Start with the variable resistor set at a low value, to be safe.

This simulates a high temperature, so the oven heater voltage
should be low. Start increasing the shunt resistance until you
get about 70% of the rated voltage across the heater. The voltage
will drop as the oven warms up. Stabilize it at 30-40% and look
for beam current. Increase the variable resistor to raise the
oven volts, but not much above 70%. If you don't get beam current
then this method will not work or something else is wrong.

This method depends on the oven controller being approximately
designed for any similar cesium physics package. You can measure
the heater resistance of the failing 5061 heater, no? See if the
5030 heater resistance is similar. For that matter, check the
cold resistance of the thermistors.

Remember that the beam current is independent of the oscillators.
Set up the 5061 for no modulation and open loop.

OTOH, how many companies made cesium physics packages? Check
for similarities, and if you find enough of them, you will be
confident that the method given above will work. You might
even find that the correct shunt resistance is infinity.

Come to think of it, a microwave cavity on the package that
matched the microwave generator in the 5061 would be quite a
coincidence. Or the connectors and HV connections ... Hope
the ion pumps are similar.

Caveat: Internet mail cannot tell the whole story. Details
that might have mattered are not transmitted or asked about.
What I suggested above is modeled on a thermionic emitter
of cesium ions.

Bill Hawkins

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of Hubert v. Bonhorst
Sent: Sunday, November 28, 2004 1:34 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Re:FTS 5030 cesium frequency standard

Thank you for your effort. The 5061A is not my problem. I' m in need for the
5030 diagrams. These are a real problem to find. My major problem is to know
the resistance of the heater thermistor at temperature. I do not know a
method to find this value, exept knowing the setresistor of the 5030.
Best regards,
----- Original Message -----
From: "David G. Andersen" <dga at lcs.mit.edu>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Saturday, November 27, 2004 7:48 PM
Subject: Re: [time-nuts] Re:FTS 5030 cesium frequency standard

> On Sat, Nov 27, 2004 at 06:32:46PM +0100, Hubert v. Bonhorst scribed:
>> Some time ago I bought a 5030 module for parts. Now I want to use the
>> cesiumbeamtube for a very weak HP 5061A.
>> I' m looking either for a web link to download the servicemanual or just
>> for some information where Cesium oven temp.
>> is set. A diagramm of the power supply and the board located directly at
>> the tube would be very helpful. Might be someone from the list could
>> help.
> I have the 5061A operations and service manual online at
>  http://eep.lcs.mit.edu/time/5061/5061A_ops_and_schematics.pdf
> It's a scanned PDF of the manual, and is kind of large (16M).  The cesium
> oven controller is on page 7-45 (96 in the pdf).
>  -Dave
> --
> work: dga at lcs.mit.edu                          me:  dga at pobox.com
>      MIT Laboratory for Computer Science           http://www.angio.net/
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