6
CMRR (Common Mode Rejection Ratio)
Common mode voltage is voltage present on both the COM and VOLTAGE input
terminals of a DMM, with respect to ground. CMRR is the DMM's ability to reject
common mode voltage effect that can cause digit rolling or offset in voltage
measurements. This series has a CMRR specification of >60dB at DC to 60Hz in ACV
function; and >120dB at DC, 50 and 60Hz in DCV function. If neither NMRR nor CMRR
specification is specified, a DMM's performance will be uncertain.
4) OPERATION
CAUTION
Before and after hazardous voltage measurements, test the voltage function on a
known source such as line voltage to determine proper meter functioning.
DC Voltage, AC Voltage, & Hz Frequency functions
mV function defaults at DC. Press SELECT button momentarily to select AC. Press the
Hz push-button momentarily to activate or to exit Hz.
A
A A
DCV
ACV
Hz
Note: Input sensitivity varies automatically with function range selected before activating
the Hz function. mV function has the highest (300mV) and the 1000V range has the
lowest (300V). It is recommended to first measure the signal voltage (or current) level
then activate the Hz function in that voltage (or current) range to automatically set the
most appropriate trigger level. You can also press the RANGE button momentarily to
select another trigger level manually. If the Hz reading becomes unstable, select lower
sensitivity to avoid electrical noise. If the reading shows zero, select higher sensitivity.
