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Turn Auto Ranging OFF
Turning auto ranging OFF makes the E1326B take all of its measurements
on a fixed range which results in fast and predictable measurement times.
Also, auto ranging must be turned OFF in order to set a 10 s aperture time.
Auto ranging is turned OFF when a numeric value or
MIN | MAX
is
specified for the
range
parameter of the
,
,
<
>
CONFigure
MEASure
,
, or
[SENSe:]RESistance:RANGe
[SENSe:]VOLTage:RANGe
[SENSe:]VOLTage:AC:RANGe
command. Auto ranging is directly
controlled by the
,
[SENSe:]VOLTage:RANGe:AUTO ON | OFF
, or
[SENSe:]VOLTage:AC:RANGe:AUTO ON | OFF
command.
[SENSe:]RESistance:RANGe:AUTO ON | OFF
You can verify the auto range mode by querying the E1326B as to its auto
range status using the following commands:
[SENSe:]VOLTage:RANGe:AUTO?
[SENSe:]VOLTage:AC:RANGe:AUTO?
[SENSe:]RESistance:RANGe:AUTO?
Decrease Aperture
The aperture time is the amount of time that the input signal is integrated.
Time
The available choices are 10 s, 100 s, 2.5 ms, 16.7 ms, 20 ms, 267 ms,
and 320 ms. The smaller the aperture time, the faster the readings are taken.
The 10 s aperture time can only be entered if auto ranging is first turned OFF.
A disadvantage to faster aperture times is that increased noise will be
present in the measured values. The most common source of noise is from
AC power sources.
The magnitude of noise from AC power sources is commonly many
milli-volts. If the signal being measured is large enough, then the noise may
not be significant. However, if the signal being measured is in the
micro-volt range, then noise becomes a factor.
The E1326B default aperture time is 16.7 ms in countries with 60 Hz power,
or 20 ms in countries with 50 Hz power. Integrating for one or sixteen
power line cycles causes the E1326B to reject power line frequencies that
are coupled into the measured signal. For example, the specification of
60 db of normal mode rejection will cause 1 mV of noise to be reduced to
1 V of noise.
Appendix D
Measurement Speed and Accuracy Tradeoffs
275
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