Sigma Tau H-Maser channel data, part 1.

The Sigma Tau Hydrogen Maser transmits 32 channels of heath and status voltage readings over RS-232. In my lab these values are currently queried and logged every ten minutes. When the lab's thermal stability problems are solved this can be reduced to once every few hours.

The past 200 days of maser channel data is quite a mess so to begin with let's have a look at just two days. I had not plotted maser channel data for many months (it's too much manual work) but maser performance was poor this week and I thought I should take a look at all the channel data.

As expected there are significant environmental temperature effects. No wonder the maser is having trouble getting down to the low 15's. The maser actually performed better for some tau last year when there was no HVAC at all.

Plot of all channels

Blindly plotting all channels together gives the following chart.

Of all the channels it turns out ten of them clearly show temperature effects. Of these 5 show large variations and 5 show small variations.

Plot of interesting channels

All the big wiggles follow periodic changes in lab temperature. The lab is still experiencing several degree changes as the A/C turns on and off.

The remainder of the channels pictured below vary much less.

Below is a close-up of the lower half of the plot.

Two more close-up plots. IF and REG move as mirror images of all the other plots.

and lastly, showing IF and CAV more clearly:

More plots

At the same scale the remaining 5 channels appear as almost flat lines. However, zooming in shows temperature effects.

Lab Ambient Temperature

The following is a plot of lab air temperature during the same two days:

In this case, the A/C was on continuously except for twice a day. A broader view, covering two weeks before this 2-day period is visible below. On many days the A/C is behaving as one would expect - many short on/off cycles:

Questions Answered

    Answers inserted below.   The errors you point out are due to changes in circuit monitor points without changing the EPROM program.  At the time, we were focused on the new microprocessor design.  Sorry for the confusion. 
-----Original Message-----
From: Tom Van Baak
Sent: Monday, March 22, 2004 4:09 PM
To: Bryan Owings
Subject: maser channel data questions

Hi Bryan,
I'm comparing my #208 channel data with a maser at NIST and have a few questions.
channel 12 - On my maser the RS-232 CML command labels this "AVE" but NIST and my manual calls it TS (Thernal Shield). Based on a plot of the data I think mine is TS not AVE. Could it be that the maser CPU is mislabeling the channel? 
Channel 12 is the thermal shield heater. 
channel 16 - STC Source Temperature Control - should this vary in the same pattern and about the same amplitude as other external temperature channels such as OO (Outer Oven) and TP (Top Plate)? 
Yes this is the temperature control for the Pirani gauge that maintains the reference temperature for the hydrogen pressure sensor.  It typically reflects room temperature changes, although with slightly less resolution. 
channel 20 - CPU says MP1, manual says MP. Manual says this should be 19.7 volts but mine is always around 23.7 volts. Is this ok? 
Old power supply design used ~20 volts, new design uses ~24 volts. 
channel 21 - On my maser the RS-232 CML command labels this "MP2"  but my manual calls it AVE. Another CPU mislabel? 
Channel 21 is the averager.  It varies between 0 and 5 volts, and is really only useful when viewed from the front panel.  It can give some indication of the auto tuner action if the register has been reset, or the cavity temperature reset. 
channel 25 - AUX - the manuals says this is open but my AUX follows closely with OO anf STC. Do you know what it is actually measuring? NIST calls this AUC/MFS - what is MFS? 
On the NIST masers this was actually the magnetic field servo.  We installed these on a few masers in the 1990s.  On your maser this is the bottle temperature control.   This heats the bottle that supplies the hydrogen to the maser to about 50 degrees.  This value typically follows the room temperature.
// CML output example:
      0   IF:+05.237           13 VCOh:+03.566
      1  REG:+03.777           14   MF:+00.517
      2  VCO:+00.054           15  VPC:+05.904
      3  VIh:-00.045           16  STC:+013.27
      4  VIo:-00.020           17   Pd:+007.37
      5   LO:+00.371           18  VSc:+019.30
      6  CAV:+04.982           19 VBat:+027.08
      7   OO:+13.516           20  MP1:+023.69
      8   LS:+17.154           21  MP2:+001.80
      9   TP:+05.493           22  AC1:+026.87
     10  ISe:+00.600           23  AC2:+026.82
     11 IBat:+00.015           24  DCX:+000.08
     12  AVE:+04.181           25  AUX:+013.59



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