ES51967
6,600 Counts Auto DMM
1.1.2 HCF signal detection
ES51967 provides detection of high-crest-factor (HCF) signal in ACV mode. ES51967
senses the signal and determines it as HCF if the Vpp is large enough. Once the signal
is determined as HCF, ES51967 will jump up one measuring range regardless of current
measurement value. It takes 60ms to jump one range up. The jumping up process will
continue until the maximum range is reached. With HCF detection, a more accurate
result could be obtained. For example, when a input signal with Vpp=300V,
Vrms=60V(CF=5) was applied, traditional DMM might stay at 66V range but shows
counts with the amount of error up to 10% or even bigger. The error rises from limited
input/output swing at internal ADC. With HCF detection, DMM will stay at 660V range
and exhibits more accurate results.
In addition to accuracy improvement, HCF will speed up the measuring process for
high voltage signals. For example, a 1000Vrms is applied, ES51967 will take about
180ms (3 HCF jumps) to enter 1000V range. And it takes 1 or 2 measuring processes to
obtain the stable result. Thus a stable LCD reading could be obtained within 1 sec.
In determining whether the input signal is HCF, ES51967 senses the signal at VR1 for
fast response. However if a signal consists of a small ac part and a large enough dc part,
ES51967 might incorrectly treat it as HCF. This could incur range-looping phenomenon,
i.e., the measurement could not settle to a specific range. When this phenomenon
happens and keeps over 5 seconds, ES51967 will change the UL level to 460 or lower
counts (the default UL level is 500 counts). The measurement range will stay at the
higher one mostly, so the range-looping phenomenon will not occur again.
V2.6
7
08/10/06
CYRUSTEK [ Cyrustek corporation ]
