58542 VXIbus Universal Power Meter
A-12
Publication 21555, Rev. E, September 2002
A.4
Reading Power Measurement Examples
This section gives as quick start in performing measurements. Therefore, the easiest measurement
commands are in the first example, MEAS#? in NORMal Mode. This may not be the optimum 58542
configuration for the user’s application. There are three example groups, NORMal Mode, SWIFt Mode,
and BURSt Mode. The use of the three 58542 measurement data commands, MEAS#?, READ#?, and
FETCh#? are explained in detail under the NORMal Mode, which is the meter’s power-on default
mode.
SWIFt and BURSt Mode measurements use only FETCh#?, not READ#? or MEAS#?. In this getting
started section, high speed SWIFt and BURSt Mode examples are few in number and brief in
description; detailed information on high speed power measurements can be found in Section A.8
(High Speed Measurements).
A.4.1
Reading Power Measurements Example 1
The following program configures the power meter for single channel operation, and uses the MEAS#?
command to perform limited Auto-Configuration and return power measurement data in NORMal
Mode. Prior to executing the measurement cycle, the MEAS#? command performs low level
configuration functions for averaging and trigger sequence arming automatically. Use MEAS#? to get
started performing power measurements quickly. Typically, MEAS#? will satisfy most power
measurement needs; however, more advanced power meter users of NORMal Mode may prefer lower
level controls of the READ#? command and the higher measurement rates of the FETCh#? command.
High speed measurements are performed using the SWIFt and BURSt Modes, not NORMal Mode.
Note that the MEAS#? command’s measurement response speed is slower at very low power levels and
faster at high power levels. This is due to a chopper stabilization system used in the NORMal Mode
(also used in SWIFt Mode, but not BURSt mode) and Auto-Averaging when using
SENS#:AVER:TCON REP. At the most sensitive gain ranges, chopper stabilization allows the very
small voltages from the power sensor to be accurately measured. Also, at lower power meter gain ranges,
Auto-Averaging automatically adds additional averaging to counter the effects of noise in the
measurement signal. The extra time required to perform these Auto-Averaged measurements will not be
apparent unless switching the default averaging control, SENS#:AVER:TCON MOV, to
SENS#:AVER:TCON REP.
When using the MEAS#? command, Auto-Averaging is automatically set to ON. If another part of
programming was using manual averaging, be sure to turn Auto-Averaging back off
(SENS#:AVER:COUN:AUTO OFF) before exiting the section of the program code using MEAS?
When operating in NORMal Mode the user can always use the SENS#:AVER:COUN? query to find out
the current averaging value for a particular sensor, and the SENS#:AVER:COUN ### command to set a
higher or lower averaging value.
260
ASSIGN @Pwr_mtr to 70101
270
CLEAR @Pwr_mtr
280
WAIT 1
290
OUTPUT @Pwr_mtr;CALC1:MODE NORM! Can ONLY send Configuration Commands in Normal Mode!!
300
OUTPUT @Pwr_mtr;CALC1:POW 1
! Channel 1 configured to measure sensor 1 power
310
!
320
OUTPUT @Pwr_mtr;SENS1:CORR:FREQ 1.44E9
! Applies Cal Factor for 1.44 GHz to measurement data.
330
!
340
FOR I=1 TO 10
350
OUTPUT @Pwr_mtr;MEAS1?
! Measures Power at sensor.
360
ENTER @Pwr_mtr;Rdg
370
PRINT Rdg
380
NEXT I
390
!
510
END
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