VNA Master™Programming Manual : Power Monitor Commands : :TRACe Power Monitor Subsystem
 
:TRACe Power Monitor Subsystem
This subsystem contains commands pertaining to the Vector Voltmeter mode.
Trace Header Transfer
:TRACe:PREamble?
Description
Returns trace header information. The response begins with an ASCII header. The header specifies the number of following bytes. It appears in the format #AX, where A is the number of digits in X, and X is the number of bytes that follow the header.
Parameters are returned in comma‑delimited ASCII format. Each parameter is returned as “NAME=VALUE[UNITS]”. Note that the parameters that are returned depend on the firmware version and that this document does not cover all parameter values that are returned by the command. Refer to Table: Trace Header Parameters.
For the example response, the serial number (SN) is 83320013 and is returned as “SN=83320013”. Refer to the following section, Example Response Format:.
Syntax
:TRACe:PREamble?
Cmd Parameter
NA (query only)
Query Response
<char> (returns block data)
Front Panel Access
NA
 
Example Response Format:
[#800000414SN=83320013,UNIT_NAME=,TYPE=DATA,DATE=1999‑11‑30‑02‑00‑01‑42,APP_NAME=MWVNA,APP_VER=T0.00.1001,PM_RELATIVE=1.000000,PM_OFFSET=0.000000,PM_UPPER_THRESHOLD_STATE=0.000000,PM_LOWER_THRESHOLD_STATE=0.000000,PM_UPPER_THRESHOLD=0.000000,PM_LOWER_THRESHOLD=0.000000,PM_DBMUNITS=0.000000,PM_ZERO=1.000000,PM_DBUNITS=0.000000,PM_DATA=– 200000.000000,PM_STATUS=1.000000,PM_ZERO_DATA=– 200000.000000,PM_REL_DATA=– 200000.000000,]
 
Trace Header Parameters
Table: Trace Header Parameters describes parameters that can be returned by the :TRACe:PREamble? command.
Trace Header Parameters  
Parameter Name
Description
SN
Instrument Serial #
UNIT_NAME
Instrument name
DATE
Trace date/time
APP_NAME
Application name
APP_VER
Application firmware (FW) version
PM_RELATIVE1
Relative State (Off/On), where 0 is On and 1 is Off
PM_OFFSET2
Offset value
PM_DBMUNITS
Specifies the unit (dBm or watts), when Relative is Off, where 0 is returned for “dBm”, and 1  for “watts”
PM_DBUNITS
Specifies the unit (dB or Percent), when Relative is On, where 0 is returned for “dB”, and 1  for “Percent”
PM_ZEROa
Zero State (Off/On), where 0 is On and 1 is Off
PM_DATA3
Power Monitor reading
PM_ZERO_DATA4
Zero data
PM_REL_DATA5
Reference data
1 For both PM_RELATIVE and PM_ZERO, the :TRACe:PREamble? command returns 0 for On, and returns 1 for Off. This is not the same as the values that are returned from :CALCulate:PMONitor:RELative[:STATe]? and from :CALCulate:PMONitor:ZERO[:STATe]?, where 0 is returned for Off, and 1 is returned for On.

2 The value that is returned by PM_OFFSET is in units of millidecibel (mdB). (For example: When “1” is returned, the measurement value is 1 mdB. When “2000” is returned, the measurement value is 2000 mdB, or 2 dB.)

3 The value that is returned by PM_DATA is in the units that have been set with the Units command (:CALCulate:PMONitor:UNITs DBM|WATT|DB|PERCent).
If the set Unit is dBm or percent or dB, then the returned value is 1000 times the unit value.
If the unit is watt, then the returned value is 10 times nW (in other words, the units are in 0.1 nanowatt (0.1 nw) increments). Examples:
When the unit is in percent, and 1000 is returned, then the measurement value is  1 percent.
When the unit is in dB, and – 1000 is returned, then the measurement value is – 1 dB.
When the unit is in dBm, and – 1000 is returned, then the measurement value is – 1 dBm.
When the unit is in dBm, and – 4600 is returned, then the measurement value is – 4.6 dBm.
When the unit is in watts, and 1 is returned, then the measurement value is  0.1 nW.
When the unit is in watts, and 3500000 is returned, then the measurement value is 350 µW.

4 The value that is returned by PM_ZERO_DATA is in 0.1 nanowatt (0.1 nw) increments. (For example: When “1” is returned, then the measurement value is 0.1 nw. When “20” is returned, then the measurement value is 2.0 nw.)

5 The value that is returned by PM_REL_DATA is 1000 times the unit value in dBm (in other words, the units are in 0.001 dBm increments, or 1 millidBm (mdBm) increments. Examples: 
When “1000” is returned, then the measurement value is 1 dBm.
When “20000” is returned, then the measurement value is 20 dBm.)