24
Operation
indicate when the voltage and/or current fall below their minimum
values. If an input value falls below the bottom of the lowest range
in auto-range mode, or below the bottom of a held range, the display
will begin to flash. Measurements can still be made, but the input is
outside of its specified range and accuracy cannot be guaranteed. If
the input falls to a value too low to actually permit a measurement,
the display will indicate "Input Low".
When making measurements using any of the operating modes of
the 918B, you can "freeze" the values for all measured parameters
by simply pressing the "HOLD" button. You can then switch
between all of the different modes and determine their respective
values at the time "HOLD" was pressed. Pressing "HOLD" a second
time restores the instrument to normal operation.
Recording of minimum and maximum values is suspended for any
period of time that the hold function is active. However, all
previously recorded values are retained. Refer to section 3.2 for
more information on minimum and maximum value recording.
2.7 Measurement of Volt Amps Reactive (Reactive Power)
Volt-amps-reactive is a parameter that is similar to volt amps, but
which takes into account the phase angle between the voltage and
current. Volt-amps-reactive is defined as the product of the rms
voltage, the rms current, and the sine of the phase angle between
them. The basic unit for volt-amps-reactive is the var. Using the
supplied 1000:1 current transformer, the 918B is capable of meas-
uring var values of up to 20,000. (For instructions on using other
current transformers with different ratios, refer to section 2.2.1.1).
For measurement of vars with the 918B, both the voltage and the
current inputs are used.
CAUTION
Do not exceed ±25 volts peak, with respect to earth
ground, on the (-) voltage input. The 918B is designed to operate
with the (-) input connected to earth ground or circuit neutral.