Integrating A to D Converter
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8-2
In order to be able to switch measurement ranges, the input circuit is also equipped
with resistors and shunts.
The fast automatic ranging causes a prompt range switch (<5ms) whenever the meas-
urement range overflows.
8.2 Integrating A to D Converter
For the highest possible resolutions, the AD converter is an integrating converter
whereby the direct voltage is converted to a sequence of pulses.
The PREMA Multiple Ramp Technique for analog to digital conversion (GPD
#2114141, US Patent 3765012) is the basis for a dependable Digital Multimeter with
exceptional linearity and extraordinary long-term accuracy using continuous integra-
tion of the measured signal without distorting interruptions.
Diagram: Conceptual Circuit Diagram for “Integrating Converter”
The input current which is to be measured is applied continuously to the integrator. At
periodic intervals the current from the reference voltage source with opposite polarity
discharges the capacitor C.
During the discharge time the pulses of a clock oscillator are counted until the com-
parator detects the passage through zero and then switches off the reference current.
This method of A/D conversion has high linearity, because it is not necessary to
switch the measured current. Methods requiring switching of the input voltage are
disturbed by the stray capacitances of the switch which cause an error depending on
the input voltage and thus produce nonlinearity.
R
R
Ue
C
Reference
Integrator
Com-
parator
Logic
Circuit
PLL
Line Phase
