Operation
29
Operating Ranges
For voltage inputs, the 918B has four different operating ranges. For
current inputs, the 918B has three different operating ranges.
Depending on the levels of voltage and current applied to the inputs,
the instrument may automatically switch between ranges. This range
switching is internal, and may or may not be evident in the display.
Automatic range switching can be defeated, using range hold. Refer
to section 3.1, "Automatic and Manual Range Selection", for a
description of the internal ranges, the display ranges, auto-ranging
operation, and range hold operation.
In the “watts” mode, minimum values of voltage and current must
be present at the inputs to maintain accuracy. The 918B display will
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".
Hold Mode
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.
Min / Max Readings
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.