Agilent Technologies 34420A, Руководство пользователя

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Null (Relative) Operation
When making null measurements, also called relative , each reading is the
difference between the input signal and a stored null value. You could,
for example, make a more accurate two-wire ohms measurement by
shorting the test leads and pressing
Null
to remove the test lead
resistance. See also “To Make Null (Relative) Measurements,” on page 45.
Reading = measurement – null value
•
The null value is adjustable and you can set it to any value between
0 and
±
120% of the highest range, for the present function.
•
The null value is stored in volatile memory; the value is cleared when
power has been off or after a remote interface reset.
•
Each function and channel has an independent null value. For voltage
measurements, each input channel has an independant null.
Temperature measurement null is applied to all temperature
measurements (if you change the probe type, null is still enabled and
applied). The null for resistance measurements applies to both 2-wire
and 4-wire measurements.
•
The null value is stored in the meter’s Null Register. There are two
ways you can specify the null value. First, you can enter a specific
number into the register from the front-panel menu or from the remote
interface. Any previously stored value is replaced with the new value.
If you are operating the meter from the front panel, entering a null
value also turns on the null function.
The second way to enter the null value is to let the meter store the
first reading in the register. Press the
Null
key to make the
displayed measurement the null value and enable the Null operation.
After you enable null, the first reading displayed will be zero. If you
entered a number into the register, as described in the paragraph
above, the first reading
does not overwrite the stored value.
•
Since an independent null value is stored for each input channel,
difference or ratio functions also use these null values. Additionally,
when using the difference function, an additional difference null can
be applied (the difference null is only available from the front panel).
See page 67 for a description of how null is applied to difference and
ratio functions.
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Chapter 3 Features and Functions
Null (Relative) Operation
77