Datasheet

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A GREATER MEASURE OF CONFIDENCE
Digital Filtering — NPLC — Line Cycle Synchronization — Autozero — Low Ohms Measurement
SWITCH/MEASURE SYSTEMS
14
Integra Series Multimeter/Switch Systems
Digital Filtering
For each major measurement function, users can employ either averaging or advanced digital filtering to
reduce noise and increase the effective resolution.
Averaging Filter
The averaging filter operates over a range of from two to 100 readings. All readings included in the filter
range are weighted equally. A step input of any size will ramp up linearly to the final value after obtaining
the number of readings specified by the user. The averaging filter may be configured as either a moving
averaging or as a repeat filter. Operation over the GPIB bus is often done in “repeat” mode to ensure that
all readings are fully filtered. Also, taking filtered measurements in repeat mode requires only one trigger,
simplifying programming. Only the repeat filter can be used while scanning.
Advanced Filter
When a DMM is used in bench mode, it’s often desirable for it to respond immediately upon connection
to a test point, without the slow response associated with an averaging filter. The advanced filter address-
es this need by providing a filter reset level. If the measured value deviates significantly from previous
values, the filter is reset to the new value, and filtering is restarted. In this way, the user can set the filter
reset level just above the maximum noise level anticipated and the multimeter will respond to new values
immediately.
NPLC
Selectable power line cycle integration allows the user to specify the number of power line cycles (NPLC)
over which to integrate (1, 5, 10, etc.). Use of line cycle integration provides rejection of noise from line
cycle interference, the most common source of noisy readings. In general, the longer the integration time
chosen, the greater the noise rejection will be. The system can also be set to less than 1 NPLC integration
time, as fast as 0.002 NPLC (~33µs at 60Hz) in the Model 2701 and 0.01 NPLC (~167µs at 60Hz) in the
Model 2700 and 2750 for faster data measurement (but without power line noise rejection).
Line Cycle Synchronization
To attain the highest possible line cycle noise rejection, it is important to trigger
the reading at the beginning of a power line cycle. The system can be set to start
a measurement precisely when the power line signal crosses zero (see Figure
7). This function increases the normal mode noise rejection 30dB, providing an
additional ×30 reduction in noise due to line cycle interference.
Autozero
Internal autozeroing is used to maintain the best measurement performance.
The advanced firmware design does the required calculation, such as CJC com-
pensation for thermocouple measurements with the 7700, 7706, 7708, and
7710, automatically in the background. This enables the Integra system to provide faster reading rates
(competitive products spend half their measurement time validating their own zero). Autozero can be
disabled to increase measurement speed, but this may result in greater measurement uncertainty.
Low Ohms Measurement (Model 2750 only)
The Model 2750 can measure low ohms on all of its switch/control modules that have multiplexers or
matrix configurations. The four-wire ohms measurement supports low ohms measurements down to the
1Ω range, with micro-ohm resolution. Measurements can be accommodated through ribbon cable or
discrete wiring. On four-wire ohms measurements, up to five additional ohms of cable/switch card resis-
tance can be tolerated per cable lead. This allows the use of ribbon cable without overloading the range.
1 PLC
A/D
Conversion
A/D
Conversion
Trigger
# 1
Trigger
# 2
Reading
Done
Reading
Done
Figure 7