E N G L I S H
35
Measurement:
AC+DC dual display
Menu key:
AC+DC or AC/DC
(press to toggle)
Connect leads:
(fig. A)
Primary display:
AC
Secondary display:
DC
*dBm readout = 10 x log (primary display
readout 2/R), where R = 600 Ω (default)
dB readout = 20 x log (primary display
readout/ref), where ref = 1V (default).
When measuring voltage, the meter acts like a
10 MΩ impedance in parallel with the circuit.
This loading effect can cause measurement
errors in high-impedance circuits. In most
cases, the error is negligible (0.1% or less) if
the circuit impedance is 10 kΩ or less.
AC Voltage Measurements
All pushbutton features are available in this
function. The On Screen Menu Selection
accesses decibel (dBm or dB) measurements.
dB (dBm or dB V) Measurements
in AC Voltage Function
The AC Volts function allows you to display
readings as deviations in dB (decibels) above
or below an established reference level. Set
up dB measurements by using the On Screen
Menu Selection buttons when measuring
AC volts. The dBm (or dB V) value appears
in the secondary display and the AC reading
appears in the primary display. Normally, dB
is measured as dBm, which is a measure of
decibels relative to 1 milliWatt. The meter
assumes a resistance of 600 Ω in making this
calculation.
This resistance can be set for any value from
1 Ω to 1999 Ω by using the set-up menu
selection buttons.
When measuring dB V, the reference voltage
can be set for any value from 0.1000 V to 5.0000
V by using the set-up menu selection buttons.
dB = 20 x log (Vx ÷ Vr)
1. For dBm, Vr is the voltage across the
reference resistance
a 1 milliWatt. For example, Vr would be
0.7746 V with a
600 Ω reference resistance.
2. For dBV, the reference voltage is 1 V.
DC Voltage Measurements
All pushbutton features are available for a
standard DC Volts reading
Both AC and DC Voltage
Measurements
When a DC volts function is selected, the
meter can display the combined AC + DC
(RMS) value or AC and DC components of
a signal separately by using the On Screen
Menu Selection button. When the meter
shows AC over DC (AC voltage in the primary
display and DC voltage in the secondary
display), the other pushbutton functions just
except the RANGE button are not available.
Application: Using AC + DC and
AC/DC in Volts Mode
Summary of Contents for UD87
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