Fluke 2638A User Manual

Input and Channel Configuration
Mx+B, Alarms, and Channel Options 3
3-33
NPLC
NPLC (Number of Power Line Cycles) is a user defined measurement speed selection
used to filter out induced ac signal noise and other inherent noise signals (line frequency
noise typically) on dc voltage, dc current, and resistance channels. It gives the user fine
control of the measurement time for either faster speed or better accuracy. Lower NPLC
increases the scan speed, but results in lower measurement accuracy. Higher NPLC
improves the measurement accuracy, but reduces the scan speed.
Higher NPLC settings are necessary in some precise measurement applications where
power line induced ac noise can affect precise dc signal measurements. Induced ac noise
is usually not uniform and requires multiple samples to accurately read the induced ac
signal. The more samples (the higher the NPLC setting), the better the ac noise can be
counteracted and filtered out. To increase the measurement accuracy and to better filter
the ac noise, the NPLC setting can be manually increased so that the Product samples the
ac noise signal over multiple cycles to get a better average of the signal.
In summary, when higher NPLC settings are set, the measurement value is more accurate,
but the tradeoff is that it takes longer for the Product to complete the measurement (see
“About Scan Timing and Sampling” in Chapter 5). For applications where ac noise will
not affect the test outcome (such as a true or false digital logic), a lower NPLC setting is
recommended for faster measurements.
Input Impedance
This setting is used to set the input impedance on the channels. For the 100 mV, 1 V,
10 V dc voltage function, there are two available choices: 10M or >10G. The default
setting is 10M.
Bandwidth
This setting is used to select the bandwidth of ac filter for ac voltage and ac current
functions. The available choices are: 20Hz or 200Hz. The default setting is 20Hz.
Display As
This setting is used to set the display to show temperature or the mV equivalent for
thermocouple channels.
Open Detect
This setting enables the Product to automatically detect an open circuit in the probe. This
setting only shows in a thermocouple channel.
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Fluke 2638A Specifications

General

Resistance Range	0 to 100 MΩ
Power Supply	100 V to 240 V AC, 50 Hz to 60 Hz
Voltage Range	±300 V
Resolution	6.5 digits
Memory	USB
Interface	USB, Ethernet
Display	Color
Measurement Types	DC voltage, AC voltage, resistance, DC current, AC current, frequency, temperature