Integration/Aperture Time; Auto-Zero - VTI Instruments Metek EX1202 User Manual

X = Resolution/Range
Where Range =100V if userRange=300V, =1A if userRange=3A, = userRange
otherwise
if (X <= 1e-6)
{
numberOfPLC=10;
}
else if (X <= 1e-5)
{
numberOfPLC=1;
}
else if (X <= 1e-4)
{// 4.5 digits
numberOfPLC=0.1;
}
else
{// 3.5 digits
numberOfPLC=0.01;
}
apertureTime=numberOfPLC/PowerLineFrequency;
Note that the EX1200 DMM's resolution is related to aperture time and can be modified to set this
property.
NOTE When the DMM is set to measure ac voltages using Low/Medium filter option, the data is
automatically measured with 6½ digit accuracy.
I /A
NTEGRATION PERTURE
The EX1200's DMM uses a slope integrating ADC to quantify the analog signal levels into digital
values. The digital bits of resolution are directly proportional to the amount of time used to
integrate the signal.
Integration time is typically specified in number of power line cycles (PLC), except in the case of
frequency and period functions. When integration time is selected as a whole number of PLC, this
helps increase the rejection of common mode and normal mode power line noise. Aperture time is
related to PLC, but is a read-only property and cannot itself be modified. Aperture time is, instead,
controlled by manipulating the resolution. The integration time can be changed by using the
resolution property. This relationship is defined by the algorithm in the Resolution discussion
above.
For frequency and period measurements, resolution is set by specifying the aperture time. The
aperture time for the frequency and period functions default to 100 ms. Valid aperture times vary
with the selected resolution: 10 ms for 4½-digits, 100 ms for 5½-digits or 1 s for 6½-digits.
Since the resolution, integration/aperture time, and number of PLC settings are inter-related, some
consideration must be made when configuring these features. The last of these related parameters
to be defined determines the actual resolution of the measurement.
A -Z
UTO ERO
The auto-zero function greatly enhances the accuracy of the measurement, especially when the
ambient temperature is constantly changing. When auto-zero is enabled (auto-zero ON), the
multimeter internally disconnects the input signal following each measurement, takes a "zero"
reading, and then a fixed reference reading. These three readings are combined to give a high-
accuracy measurement value. Auto-zero eliminates the negative effects of internal offset and gain
errors that occur with temperature changes and aging. Auto-zero requires two background
measurements so the DUT measurement rate will be reduced.. As is true with resolution, however,
performing auto-zero requires two additional measurements to be taken, decreasing the overall
reading rate speed.
Basic EX1200 DMM Operation
T
IME
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