The Reference
Frequency
In many data acquisition applications, DC voltage and resistance
measurements are often made in the presence of normal mode noise. This
type of noise emanates from the surrounding environment, primarily from
50 Hz and 60 Hz power lines. The HP E1326B/E1411B multimeter is able
to reject normal mode noise by using an integrating analog-to-digital (A/D)
converter. The integration process averages out the power line related noise
over an integer number of power line cycles (PLCs) during the A/D
conversion. The multimeter’s ability to reject noise at the power line
frequency is expressed in terms of normal mode rejection (NMR).
Setting the Reference
Frequency
In certain applications, the multimeter’s power line frequency may be
different from the line frequency of the device being measured. Assume,
for example, the multimeter has a power line frequency of 60 Hz and the
device being measured has a line frequency of 400 Hz. Normal mode
rejection can be achieved by setting the reference frequency to 50 Hz.
This is done with the command:
CALibration:LFRequency
frequency
| MIN | MAX
frequency is power line frequency. Settings are 50 or 60.
MIN
sets the minimum power line frequency (50 Hz).
MAX
sets the maximum power line frequency (60 Hz).
The reference frequency is set to 60 Hz at the factory. The setting is stored
in non-volatile memory and is changed only when
CALibration:LFRequency
is executed.
Querying the
Reference Frequency
The reference frequency is queried with the following commands.
See Chapter 5 for additional information about these commands.
CALibration:LFRequency?
CALibration:LFrequency? MIN | MAX
Chapter 2
Configuring the HP E1326B/E1411B Multimeter 27
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