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Concept of the HM8112-3
Reference
The integrated AD converter has to be connected to a reference.
The characteristics of this reference determine the long term
stability of the instrument. The reference of HM8112-3 is therefore
a high precision reference device.
Integrated AD converters
Converters applying the multi slope method are used for AD
conversion.
Moving average
The value determined by the AD converter could be displayed
without prior computations, also the average calculated from
n – values could be shown. First of all 1 to n values will be
logged. Averaging over these values will be done, and sub-
sequently this average will be displayed. After 120 values the
next value n+1 will be quantified by the AD converter. The
primary measured value 1 will be abolished and a new average
will be calculated from the remaining values ( 2 to n) and from
the new value n+1. This has the advantage that peaks and
interferences will be smoothed.
Measurement of alternating values
Frequency, period
Frequency and period are both measured by a pulse-counting
circuit. Time base is 1 second. The first falling edge triggers
the measurement and starts the counter. For one second every
falling edge will trigger a counting pulse. After expiry of this
term the measurement circuit will wait for the next zero point.
Hence the signal's period is measured. The time will be
measured until the next zero point occurs. The measurement
result determines the frequency of the signal and the period
will be calculated from the frequency. This combined
measurement of the number of zero points and of the period
of a signal allows the measurement of very small as well as
I n t r o d u c t i o n t o t h e o p e r a t i o n o f t h e H M 8 1 1 2 - 3
very high frequencies within a reasonable time. Applying of a
DC voltage results in a frequency displayed of 0 Hz.
As the period is calculated from the measured frequency
division by zero will be made. Therefore the instrument will
display „INF" if the period of a DC voltage is measured („INF"
= infinity).
RMS rectifier
The AC voltage is measured by a high precision RMS rectifier
device. This device gauges a DC voltage proportional to the
applied AC voltage. This DC voltage is equivalent to the true
RMS value of the AC voltage.
Measurement of the crest factor
For crest factors exceeding 7 an AC voltage or current
measurement will be incorrect due to the true RMS converter.
Introduction to the operation of the HM8112-3
Especially before the first operation please pay attention to
the following points:
–
The line voltage, indicated on the rear panel of the
instrument must correspond to the line voltage used.
–
Operation is only allowed from 3 terminal connectors with
a safety ground connection or via isolation transformers
of class 2.
–
No visible damage to the instrument.
–
No damage to the line power cord.
–
No loose parts in the instrument.
Factory settings
The following values are set by default:
–
The measurement range is
–
The sampling rate amounts to
–
The function „1:Filter" is
–
The temperature is displayed in
–
The selected temperature sensor is
–
The data logger is
–
The RS-232 interface is
10 V
DC
100 ms
OFF
°C
PT100
OFF
OFF
41
Subject to change without notice
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