[time-nuts] Re: Datum PRS-50 monitoring software

[Tom Knox]

Hi Claude;
I am not sure if anyone addressed the Lock/Un-Lock issue, sadly what you are seeing is classic Cesium Tube end of life symptoms. Cesium Tubes do not suddenly stop working with age. They fail slowly as the signal to noise ratio increases with use. At this point when the tube begins to go in and out of lock the user normally pulls the cesium standard from service. Of course, I have seen many issues that could also cause this, so you are taking the correct path with Monitor Software to eliminate other possibilities. I would also physically inspect the boards for such obvious issues as bad caps.
I hope you get lucky and find something easily repairable. Please keep us "Time Nuts" posted on your progress.
Happy New Year;
Tom Knox
SR Test and Measurement Engineer
Phoenix Research
4870 Meredith Way Apt 102
Boulder, Co 80303
Formerly of:
357 Fox Lane
Superior Co 80027
303-554-0307
actast at hotmail.com

https://www.thedenverchannel.com/news/marshall-fire/superior-man-moving-forward-after-losing-dream-research-lab-during-marshall-fire

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________________________________
From: Jim Harman via time-nuts <time-nuts at lists.febo.com>
Sent: Thursday, December 29, 2022 9:59 AM
To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: Jim Harman <j99harman at gmail.com>
Subject: [time-nuts] Re: Datum PRS-50 monitoring software

If your RS-232 dongle has a separate USB cable, make sure the cable is
fully functional and is not a charge only type. This has tripped me up a
couple of times. You should hear the Windows "bing bong" sound when the
dongle is plugged in, and if you connect the TXD and RXD lines and type
something into a serial monitor on the PC you should see it echoed back.

Another common issue with RS-232 connections is the need for a null modem
that swaps the RXD and TXD lines, pins 2 and 3 on either the 9 pin or 25
pin connectors. If you measure the voltage on these pins, the TXD will idle
at about -5 V and the RXD will be near zero. The TXD on one side must be
connected to the RXD on the other.

And of course the baud rates must match.

On Wed, Dec 28, 2022 at 11:44 PM va2hdd--- via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hello to all members.
>
> I recently purchased a Datum PRS-50 that looks like a spare unit, almost
> mint. When I connect it to a lab PS set to 48 volts the current
> stabilise at around 0,5 Amp, the LED's light up according to the
> sequence described in the manual and the unit eventually goes into
> cesium lock with a very nice 5.000000046 MHz output.
> The cesium lock LED stays on for a while, then the unit goes in alarm,
> then back to cesium lock, then alarm ...  I suspect that the ion pump
> need to improve the vacuum in the CS tube.  I tried to use the "monitor
> 3" Windows software to watch ion pump current but I was never able to
> get it communicating both with front or rear connector, I installed the
> software on a Windows 10 PC and used a USB to RS-232 dongle.  I tried
> three different chipset USB-232 adapters with the same result.  My unit
> does not have the "TL1" option, and on page 2.2 of the manual in table
> 2.3-1 it is mentioned that without the TL1 interface I should be using
> the DOS version (Monitor.EXE).  I tried to find it but had no luck.
>
> Best regards,
>
> Claude VA2 HDD
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--Jim Harman
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