Performance Verification Tests 4
Keysight 3458A Calibration Manual 55
Calibration cycle
The frequency of performance verification depends on the instrument's usage and
the environmental operating conditions. To maintain 24 hour or 90-day
specifications, the instrument should be checked at these intervals by a metrology
lab with test capability for these accuracies. For normal operation, it is
recommended you perform performance verification every year.
Test considerations
This section discusses many of the major problems associated with low-level
measurements. Many of the measurements in this manual fall into this category. It
is beyond the scope of this manual to go into great detail on this subject. For more
information, refer to a textbook dealing with standard metrology practices.
– Test leads: Using the proper test leads is critical for low-level measurements.
We recommend using cable or other high impedance, low dielectric
absorption cable for all measurement
– Connections. It is important to periodically clean all connection points
(including the multimeter terminals) using a cotton swab dipped in alcohol.
– Noise Rejection: For DC voltage, DC current, and resistance measurements,
the multimeter achieves normal mode noise rejection (NMR)
[1]
for noise at the
A/D converter's reference frequency (typically the same as the power line
frequency) when the integration time is ≥ 1 power line cycles. You can specify
integration time in terms of power line cycles (PLCs) using the NPLC
command. For maximum NMR of 80dB, set the power line cycles to 1000
(NPLC 1000 command).
– Guarding: Whenever possible, make measurements with the multimeter's
Guard terminal connected to the low side of the measurement source and the
Guard switch set to the Open position (guarded measurements). This provides
the maximum effective common mode rejection (ECMR).
– Thermoelectric Voltages (Thermal EMF): This is a common source of errors in
low-level measurements. Thermal EMF occurs when conductors of dissimilar
metals are connected together or when different parts of the circuit being
measured are at different temperatures. Thermal EMF can become severe in
high-temperature environments. To minimize thermal EMF, minimize the
[1] Normal mode noise rejection is the multimeter’s ability to reject noise at the power line frequency
from DC voltage, DC current, or resistance measurements.
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