HP 5071A Maintenance Manual
29th
Annual
Precise
Time
and
Time
Interual
(PTTI)
Meeting
MAINTENANCE
OF
HP
5071A
PRIMARY
FREQUENCY
STANDARDS
USNO
AT
H.
Chadsey
(hc
@planck.usno.navy.mil
A.
Kubik
(tony@ simon.usno.navy.rni1)
Time
Service Department
U.S.
Naval
Observatory
Washington,
D.C.
20392
Abstract
The
US.
Naval
Observatory
(VSNO)
has
been
operating
Hewleti-Packard model
507lA
cesium-beam fraquenq standardr
for
over
five years.
During
that
period,
there have been
a
variety
of
failures
and
these devices have shown frequency
and
phase changes.
The
HP
5071A
model
primary
frequency standard oflers a
very
useful
troubleshooting tool
by
outputting the status
of
22
digerenr operating parameters.
This
paper will present
an
explanation
of
the parameters
and
show
any
correlation
of
them
with the time, frequency,
and environmental changes. This paper will also
ofet
some
indicators to predict future
device
problems.
INTRODUCTION
The
Hewlett-Packard
(HP)
model
5071A
Primary
Frequency
Standard
is a quantum
leap
forward
compared
to
the
HP
model
5061B.
Among the improvements is the
greater
frequency
stability
through
a
broader
temperature
and
humidity range.
HP
also improved
the
device's operational parameter monitoring capabilities.
No
longer
must
people enter
the
room
housing
the
device (disrupting
its
environment)
and
physically
make the measurements
on
the device.
The
new
standards
can
output
their parameters via
an
RS-232
connection
to
a
computer
for
permanent
filing
and
analysis.
49
The analysis
of
these
permanent files can range
from
a
snapshot picture
of
the
parameters to
a
time series analysis with plotting. Having the extreme long-term
history
of
the parameters has additional benefits, especially if that history extends
throughout the life
of
the standard.
USNO
has
45
standards
from
the
100,
200,
300,
400,
500,
700, and
1000
production series. Each device has its
own
"personality." Some characteristics have been correlated with production series.
This paper will present the general characteristics
of the
USNO
devices and note
where they may differ.
The
parameters will
be
discussed in the order
of
their
output.
The
more
important parameters will be noted and discussed in greater
detail.
THE
PARAMETERS
There
are
22
parameter values available via the
RS-232
connection. These
parameters are: frequency offset, oscillator control percentage,
rf
amplitude
1
percentage,
rf
amplitude 2 percentage, Zeeman frequency, C field
current,
electron
multiplier voltage, signal gain percentage, tube oven voltage,
tube
oven
temperature
error,
oscillator oven voltage, ion pump current, hot
wire
ionizer voltage, mass
spectrometer
voltage, SAW tuning voltage,
DRO
tuning voltage,
87
MHz
PLL
voltage,
UP
clock
PLL
voltage,
+12
volt supply voltage,
-12
volt supply voltage,
5
volt supply voltage, and internal temperature.
USNO
collects these data once
per
hour. The information appears
as:
MJD
48587
21:03:42
CBT
ID:
6-temp
Status
summary: Operating normally
Power source:
AC
Log
status:
Empty
Freq
Offset:
Oe-15
Osc.
control:
RF
amplitude
1:
20.2
96
RF
amplitude
2:
2emi
Freq.
E-multiplier
:
CBT Oven:
Osc.
Oven:
HW
Ionizer:
SAW
Tuning:
87MHz
PLL:
+12v
supply:
+5v
supply:
39949
Hz
1870
V
6,2
V
-8.8
V
1.0
v
3.5
v
-0.8
v
12.3
V
5.3
v
c-tieli cum:
Signal
Gain:
CBT
Oven
Err:
Ion Pump
Mass spec:
DRO
Tuning
UP
clock
PILL:
-12v
supply:
Thermometer:
-1.67
%
19.9
%
12.137
mA
28.8
%
0,OO
c
0.2
uA
9.1
V
6.8
V
2.9
V
35.0
C
-12.4
V
50
7
USNO
permanently files these values
as:
50717.007569
CBT
ID:
3128AOO110(H) /Status summary: Operating
normally Power source:
AC
/Log
status: Empty
Oe-15
29.94
26.5
25.4
39949
12.166
2553
15.4
8.3
0.00
-8.7
0.0
0.8
12.8 1.8
5.8
1.7
2.6
12.3 -12.3
5.2
41.3
A
computer program
can
sort
and
display the information
in
whatever format
is
needed. One might want several devices listed
on
one page when looking at
snapshot pictures. On the
other
hand, one might want several consecutive readings
for
a
particular device listed on one
page
to
look
for
trends. Outputting the values
to
a
plotting program
is
better for trend observation. Although the snapshot
pictures will tell if
a
device
is
operating normally, it is the plot
of
the
parameters'
history that will help most
in detecting the onset of problems and in fixing the
device when
a
failure occurs.
CLOCK
PERFORMANCE
The
frequency
offset
can
be
set
by
either
the
manufacturer
or
the
user.
Typically,
it is set to
Oe-15.
Oscillator control percentage
is
a
very
important
value to monitor. The value
can
be
positive or negative and
like
most
of
the other parameters, the value is very
characteristic
of
the device, One
standard
may have
an
oscillator
control
value
of
-8.6%
and another standard may have a value
of
-43.1%.
Neither of these
values
done
means
that the clock
is
performing
(or
will
perform)
poorly. A variation in
the
value
may
suggest a
future
failure,
and
that
will
be
covered
in
the next section.
What is important about the oscillator control percentage
for
performance
is
its
frequency
and
amount
of
change. This is
an
example
of
when continuous, periodic
readings
are needed. For example,
USNO
has had at least two
standards
that
exhibit a phase or rate change that
was
coincident with a change
in
its oscillator
control percentage. Such
an
occurrence may be due to the
standard
experiencing
an
environmental change (temperature andor humidity), a Cesium
Beam
Tube
(CBT)
change, or
a
CBT
controller
board
change,
or
it may
be
a
precursor to
a
failure.
The
rf
amps
have been found
to
have relatively constant values between
20.0
and
31.0
for
each
standard
after initial
burn-in.
(The values may change somewhat
during the first
1
112
to 2 years
of
operation.)
The values will differ slightly
from
51
one device to another. The Zeeman frequency is set at the factory and should be
39949.0.
The C field current should be between
12.0
and
12.2
milliamps
and
remain fairly constant. Again, the exact
value
will differ between standards.
The
electron multiplier voltage is another very important parameter
to
watch.
There
is
a
limit at
2553
volts.
USNO
does have a standard performing quite well
below the
lo00
volt specification found in the
5071A
owner's manual. (Its startup
voltage was about
440
volts,) Typically, our standards have
a
startup
voltage
between 1150
and
1500.
The voltage will decrease slightly and then begin
to
rise
slowly during the first two years
of
operation. The total change will usually range
from 150 to
200
volts. The voltage should continue to increase slowly after this
initial startup
period.
The absolute value is characteristic
of
the
device.
The
standard should
be
performing well if the value is changing slowly and
CONSISTENTLY
during the entire life time of the
CBT.
The signal gain should
be
constant at
14.4
percent
as
long
as
the standard is below
its
maximum electron multiplier
voltage.
When the electron multiplier voltage
reaches its
limit,
the
signal
gain
will increase to keep
the
overall
gain
constant.
The cesium-beam oven voltage depends on ambient temperature. The
USNO
standards
values are consistent between
7.5
and
8.0
volts. Actual values differ
between
devices.
The
cesium-beam
tube
error
must
be
small
(+I-
0.1
volts)
for
the
standard to
be.
operating properly.
The oscillator oven voltage typically has a value
of
-8.7
to
-8.8
volts during
normal
operation. It should change by
no
more than
0.1
volts throughout the
life
of
the
device.
The ion
pump
current should have a low startup value (typically
near
0.0)
and
remain
constant.
Some
devices, however,
are
working quite well with constant
values
of
10,20, or higher.
(USNO
has
one device working well with
an
ion
pump
current of
36.0
microamps.) This value is another one
of
those "personality"
characteristics
of
each device. A high current value
can
indicate a vacuum
or
electrical leak, that the
tube
has been
off
for a long
period,
or
that the
tube
is
contaminated. A current greater than
50
microamps
will cause shutdown.
The hot wire ionizer voltage references the voltage across the ionizer ribbon.
A
value of
1.0
is
ideal and it should
be
between
0.9
and
1.1
volts.
The
mass
spectrometer value will
range
from
10.0
to 14.0 volts. It should remain
the same value during normal performance due to environmental changes.
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