Setting The Integration Time - Agilent Technologies 3458A User Manual

Setting the
Integration Time
Note
Note
important that the specified bandwidth (particularly the specified low
frequency) corresponds to the frequency content of the input signal.
Integration time is the period of time that the A/D converter measures the
input signal. For analog AC measurements, the integration time determines
the maximum digits of resolution and, along with the specified bandwidth
affects the measurement speed. (Integration time also has a minor affect on
analog AC measurement accuracy). Analog AC measurements are defined
as AC or AC+DC voltage measurements made using the analog conversion
method (SETACV ANA command) only, and AC or AC+DC current
measurements. With longer integration times, the measurement resolution
and accuracy increases, but measurement speed decreases.
The integration time has no effect on frequency or period measurements.
For sampled AC voltage measurements (SET ACV SYNC or SET ACV
RNDM) the A/D converter's integration time is selected automatically and
the multimeter achieves the specified resolution ("Specifying Resolution"
is discussed in the next section) by varying the number of samples taken.
For analog AC measurements, you can specify integration time in terms of
power line cycles (PLCs) using the NPLC command. (You can also use the
APER command to specify integration time although it is primarily intended
for DC measurements; refer to the APER command in Chapter 6 for more
information.) The multimeter multiplies the specified number of PLCs by
the period of the A/D converter's reference frequency (LFREQ command)
to determine the integration time. For example, the period of a 50 Hz power
line is l/50 = 20 msec. If you specify 10 PLCs, the integration time is
200 msec. In the power-on state, integration time is set to 10 PLCs. In the
PRESET NORM state, integration time is set to 1 PLC. To set the integration
time for the fastest measurements (with the lowest accuracy and 4½, digits
of resolution), send:
OUTPUT 722; "NPLC 0"
To specify the most accuracy and Highest resolution (6½ digits),with the
slowest measurement speed, send:
OUTPUT 722; "NPLC 1000"
You can specify power line cycles in the following ranges:
•
0 - 1 PLC (in .000006 PLC steps for 60Hz ref. frequency or. 000005 PLC
steps for 50Hz ref. frequency)
•
1- 10 PLC in 1 PLC steps
•
10 - 1000 PLCs in 10 PLC steps
For integration times greater than 10 PLCs, the multimeter averages a
number of readings made using 10 PLCs of integration time. For example,
Chapter 3 Configuring for Measurements 67