5120A/5115A Operations and Maintenance Manual 63
For more general information about the time constant see “Chapter 5, Setting the Time Constant”
on page 41.
7.2.6.4 Setting the Allan Deviation τ
0
Value
You can set the τ
0
value using the following command:
set tau0 <value>
Where the <value> parameter is set to:
A fixed floating point number
0.001, 0.01, 0.1, or 1 (seconds)
The Allan deviation plot or table can be printed for a single τ
0
value only. To print the Allan
deviation plot for a τ
0
of 10 ms, issue the following commands:
set tau0 0.01
print adevplot
For more information about printing from the network, see “7.2.4 Printing from the Command
Port” on page 60.
To determine the current τ
0
value, use the show tau0 command. The test set will return the current
value in the format used by the set tau0 command.
7.2.6.5 Setting Frequency Counter’s Reference Frequency
See “Chapter 5, Configuring the Frequency Counter” on page 49 for general information about the
frequency counter.
To automatically set the reference frequency each time data collection starts, enter:
set referencefreq auto
To manually set it to a more precise value, provide the frequency in MHz as the last parameter to
the set referencefreq command. To set it to 5.0000003 MHz enter:
set referencefreq 5.0000003
Future show fcounter commands return the averages calculated using the new reference
frequency. The user interface table is also updated immediately. Note that show fcounter can be
used to determine what the current reference frequency is.
The reference frequency is applicable only to external signals connected to the Reference port, it
does not affect the reference frequency used in the internal reference mode featured by the 5120A-
01. The set referencefreq command can be sent while a 5120A-01 is operating in internal
reference mode, it will take effect the next time data is collected using an external reference signal.
7.2.7 Retrieving Status Information
To determine the current data collection state, enter show state. The command outputs the current
state and time constant. If the test set is in the Collecting state when the command is issued, the
duration of data collection is also output. For general information see “3.2.1 Collecting State” on
page 13.
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