User`s guide

6
4.2 Measurement mode selection
The 437B and 438A have certain delays associated
with measurement mode changes and auto rang-
ing. Some software may have made use of this fea-
ture to allow, for example, some other instrument
to settle before triggering the power meter. Such
assumptions cannot be made for the Agilent EPM
series power meters, as they are much faster and
more responsive. A typical scenario for the E4419A/B
dual channel power meter is discussed below.
100 ! The power meter is
currently measuring
Channel A and Channel B
is connected to the output
of a signal generator.
110 !
120 OUTPUT @Pm;”BP” ! Select measurement
Channel B
130 OUTPUT @Sg; ! Set signal generator
“LEVEL -10DBM” output level to -10dBm
140 OUTPUT @Pm;”TR2” ! Trigger power meter
150 ENTER @Pm;$POWER ! Read measured power
In this example, the response time of 438A may
well have been sufficient to allow the source out-
put level to settle before triggering the power meter.
However, as the E4419A/B is much more respon-
sive than the 438A, it is almost certain that in this
situation the E4419A/B would have triggered before
the source had settled. Consequently, the wrong
result would be returned. This method is therefore
not recommended. Instead consider a settling delay
after line 130 (this, of course, will be instrument
dependent) or read the status back from the source
and hold until the level has settled.
4.3 Range hold and manual ranging
When using the 8480 series sensors, the EPM
series power meter has effectively one range. The
437B, for example, has 5 ranges when used with
the 8480 series sensors. This means that when
using 437B or 438A language, both the range hold
and manual range selection commands are mean-
ingless to the EPM series power meter. These range
commands are accepted but will have no effect.
As the EPM series power meter is always in auto
range, the status message fields for the attached
sensor(s) will be set to 11 (auto range mode and in
range 1) at all times. Manual ranging in the 437B
and 438A is invariably used to obtain faster meas-
urement speed as the up/down range switching
associated with auto ranging is inhibited. Software
using manual ranging may require modification,
especially if it is making decisions based on the
status message of the sensor range fields. The
simplest cure is to remove all references to manual
ranging, as the EPM series power meter will per-
form more than satisfactorily, in terms of measure-
ment speed, in auto range.
Note: The ranging commands do have implications
when the E-series of power sensors are being used.
This is discussed later in section 4.10, “Using the
Agilent E-series power sensors.”