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
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
- LS (Lower Support Heater) is most affected by temperature changes; not
only the highest voltage reading but also the largest peak-to-peak range. The
next three lines,
- OO (Outer Oven Heater),
- BTC (hydrogen Bottle Temperature
- STC (Source Temperature Control - Pirani gauge) are all
similar in magnitude and range.
- TP (Top Plate Heater) is much lower in
magnitude but similar in range to the other three.
- TS (Thermal Shield Voltage) is both lower in magnitude and much
lower in range.
The remainder of the channels pictured below vary much less.
Below is a close-up of the lower half of the plot.
- Pd (Palladium Heater voltage) now shows the same pattern,
- TP and TS are also seen more clearly.
- IF (405 kHz second IF amplitude),
- CAV (Cavity Heater Voltage), and
- REG (Cavity Register) show the slightest deviation from a flat
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:
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
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.
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?
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
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?
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?
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?
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:
DATUM/FTS-SIGMA TAU STANDARDS GROUP
ATOMIC HYDROGEN MASER
- use TauPlot to generate live plots
- y-axis: 1V full scale, and maximum resolution
- x-axis: 1 day, 1 week, 1 month, 1 year
- record mean and sdev per day
- follow data through HVAC experiments
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