Hameg HM8112-3 Digital-Multimeter, DMM, 1 200 000 Counts 25-8112-0302 Data Sheet

51

Subject to change without notice

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8  concept of the Hm8112-3

8.1 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 there-

fore a high precision reference device.

8.2  integrated AD converters

Converters applying the multi slope method are used for AD 

conversion.

8.3  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 pri-

mary 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 in-

terferences will be smoothed.

8.4  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 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 divi-

sion 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 measu-

rement will be incorrect due to the true RMS converter.

9  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 instru-

ment 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 

10 V

DC

–  The sampling rate amounts to  

100 ms

–  The function „1:Filter“ is 

OFF

–  The temperature is displayed in 

°C

–  The selected temperature sensor is 

PT100

–  The data logger is 

OFF

–  The RS-232 interface is 

OFF

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