Atec Fluke-910, Fluke-910R User Manual

910/910R GPS

GPS­Receiver

Phase
comparator

Local
oscillator
(VCO)

Reference Out (10 MHz)

Controlled Frequency Standards

The cesium controlled frequency standard that uses

GPS technology and connectivity to provide primary

standard traceability from any location

The 910 and 910R GPS-con­trolled frequency standards
deliver a precision frequency
and pulse-per-second time
“reference which, with its many
connectivity options, can be
installed, monitored and man­aged from virtually any location.
Both models receive their long­term frequency stability from
the built-in cesium standards in
the GPS-satellite array, yet can
also provide a very high short­term stability from the built-in
oven controlled crystal oscillator
(OCXO) or rubidium oscillator (Rb).
Both the 910 and 910R are
fully traceable and extremely
accurate frequency standards
and are ideally suited for use
in many applications, including
telecommunications, calibration
and automatic test systems.

Unique traceability feature
means no more re-calibrations

Off-air frequency standards
have existed for several years.
But until now, they all have had
the same internal architecture
(Figure 1). The unit is, in effect,
a “black box,” with an antenna
input and a frequency output.
The local oscillators con­trol process (disciplining) is

hidden from the user. Typically,
users have used another fre­quency reference (for example,
a rubidium standard), a timer/
counter and a PC for logging the
deviation between the “black
box” and the frequency reference.
The concept of traceability
requires an unbroken chain of
comparisons to international
standards, on a continuing basis,
where all comparisons produce
documented results with stated
uncertainty.
Now, for the first time, a docu­menting frequency comparator
and a very stable secondary
standard are united within the
same instrument together with
the GPS receiver.
The received GPS signal is
measured continuously against
the local oscillator. Phase and
frequency deviation is stored

Figure 1. A typical “black box GPS receiver” (antenna in - reference out). Internal oscillator
offset and adjustments are invisible to the user.

Technical Data

internally and can at any time
be transferred to any PC directly
from the 910/910R or, via the
optional Ethernet interface, from
or to almost anywhere. Then by
using the GPSViewTM software
supplied with every model, a
printout of the traceability record
can be obtained. The unbroken
calibration history chain—day
by day—is maintained in the
non-volatile memory for several
years, with the current 24-hour
mean offset being displayed con­tinuously on the front panels LCD
display.
Such unique traceability to
primary standards means that
the 910 and 910R never need
to be away for re-calibration.
Thanks to this design, the very
high stability built-in rubidium
or OCXO oscillator is continuously
calibrated to the primary freq­uency standards in the US
Observatory and ultimately
UTC, in both operating modes,
disciplined or manual hold-over.

Two high-stability models to
meet your application, and
fit your budget

Fluke Calibration offers two
standard models

in its controlled
frequency standards range; the
very-high stability 910R with its
built-in rubidium atomic clock
as the local oscillator, and the
affordable 910 with its high
stability local oven controlled
crystal oscillator.

Naval

to

GPS­Receiver

High resolution
counter

Measurement
storage

(Calibration data)

Microprocessor

Rubidium
or OCXO
oscillator

Front panel display of frequency offset

1 pps Out

Reference Out (10 MHz)

To PC (RS232)

1pps

Optional Ethernet
interface

Figure 2. The Fluke Calibration 910 and 910R have built-in comparison between the GPS receiver and the internal oscillator. The frequency
offset is displayed and stored and a traceability record can be produced at any time.

Up to 13 outputs, maximizing
cost efficiency

Both models come with one 5 MHz
and five 10 MHz sinewave
outputs as standard. A one
pulse-per-second output is also
included.
If your application requires
more outputs—for example, if
several other instruments need
to be supplied from the same
frequency standard—option 70
allows you to mount five more
10 MHz outputs. Alternatively,
option 72 allows you to expand
your instrument to give five
extra 2.048 MHz outputs, which
is particularly useful in many
telecoms applications. Option
73

provides five extra 13 MHz

outputs,

the standard frequency
for GSM base station master
clocks. Another variant on output
configuration is offered through
option 71, which gives the
instrument an additional four
sine wave outputs of 10 MHz,
5 MHz, 1 MHz and 0.1 Hz, plus a

0.1 MHz square wave output.
And finally, option 75 allows
you to define your own pulse
frequency output.

Central or remote monitoring,
management and data col­lection, using the 910/910R
Ethernet-port

The 910 and 910R can both be
fitted with an optional Ethernet
communication interface (option

76) which enables on-line
access

. Using the GPSView

software supplied, it is possible

TM

to monitor both instrument and
GPS status, or even collect cali­bration data, via the internet or
any Local Area Network.
With Ethernet interface con­nectivity, distances to which
data can be transmitted become
unlimited, unlike that of any
standard GPIB or RS-232 inter­terface, thereby allowing the
910/910R to be monitored from
practically anywhere.
This means that the metro­logist or lab technician no
longer

requires a ‘floating’
laptop PC to directly perform
instrument management tasks,
as this can now be achieved
from any desktop PC, from
any location inside or outside
the calibration laboratory. It
also allows data from multiple
instruments to be simultane­ously viewed in real time.

Two high-stability operating
modes to suit your application

Most users prefer automatic
adjustment (known as disciplin­ing) of their frequency standard,
to fully eliminate long-term
frequency changes (aging).
This disciplined mode is also
the default mode in the 910
and 910R. As long as there is a
valid satellite signal, the internal
local oscillator is monitored and
adjusted and the mean 24-hour
frequency offset is always
virtually zero. However, in this
mode, the inherent short-to­medium term stability of all local
oscillators,

except rubidium, is

compromised. This is true for all
GPS frequency

references. The
received GPS signal has rela­tively large short-term frequency
variations, due to variations in
atmospheric conditions. This
means that when using the
received GPS signal for disciplin­ing the 910 (OXCO), the stability
is reduced a little for

averaging
times of 100 s to 1000 s.
In this mode, the frequency
deviation between the inter­nal timebase oscillator and the
received GPS-signal is used to
continuously adjust the oscillator
(disciplining). The resulting fre­quency offset and adjustment data
is stored in non-volatile memory
every 24-hours, to enable print­out of the traceability record. The
actual frequency offset (24h mean
value) is calculated and displayed
on the front panel.
Some applications demand
superior short-medium term
stability, especially for jitter and
wander measurements in digital
telecommunication networks.
The unique manual hold-over
mode makes it possible to switch
over temporarily from disciplined
to hold-over mode during the
actual measurement, thereby
achieving a superior frequency
accuracy at the start of the mea­surement and a superior stability
through the measurement.
Here, the internal oscilla­tor is not adjusted. This mode is
normally automatically entered
when there is no usable received
GPS-signal. This mode can also

2 Fluke Calibration 910/910R GPS Controlled Frequency Standards