
Keysight E1412A Digital Multimeter User Guide
xli
True RMS AC Measurements
Keysight E1412A Multimeter Application Information
Example
Calculate the approximate measurement error for a pulse train input with a crest
factor of 3 and a fundamental frequency of 20kHz. For this example, assume the
multimeter's 90-day accuracy specifications:
(0.05% + 0.03%).
Total Error = 0.08% + 0.15% + 1.4% = 1.6%
Loading Errors (ac volts)
In the ac voltage function, the input of the E1412A appears as a 1M
resistance
in parallel with 100pF of capacitance. The cabling that you use to connect
signals to the multimeter will also add additional capacitance and loading.
For low frequencies where
:
For any frequency
:
R
s
= source resistance
f
= input frequency
C
in
= input capacitance (100pF) plus cable capacitance
AC Measurements Below Full Scale
You can make the most accurate ac measurements when the multimeter is at full
scale of the selected range. Autoranging occurs at
10% and
120% of full
scale. This enables you to measure some inputs at full scale on one range and
10% of full scale on the next higher range (e.g., 10V on the 10V range or 10V on
the 100V range). The accuracy will be significantly different for these two cases.
For highest accuracy, you should specify the range to assure the lowest range
possible for the measurement (this turns autorange off).
Function and Range Change Internal Offset Correction
The E1412A uses an ac measurement technique that measures and removes
internal offset voltages when you select a different function or range. The next
two sections discuss two ways these offset errors can be generated and how the
multimeter deals with them.
(f Rs
)
15(106)
Hz:
Error (%) =
-100 Rs
Rs
+
1M
------------------------
Error (%) = 100 x [
1
1 + (2
f Cin
(1M
)Rs
1M
+Rs
-------------------------)2
--------------------------------------------------------------------
( 1M
1M
+Rs
----------------------
)-1]
Содержание E1412A
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