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Operation
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converter is employed, the value displayed will be true rms. For
measurement of rms ac current, the voltage input is not used.
Procedure
1.
Switch the unit into the rms ac current mode by pressing the
front panel button labeled "Arms".
2.
Connect the output of the clamp-on current transformer (CT) to
the current input of the 918B, using the supplied cable. Be sure
that the (+) and (-) terminals on the CT correspond directly to
the (+) and (-) terminals of the 918B current input.
3.
Clamp the CT around the wire carrying the current to be
measured, making certain that the jaws close completely. Note
the (+) and (-) symbols near the jaw opening, indicating the
phase relationship between the CT input and the CT output.
4.
Although not critical for current-only indication, this will be of
particular importance for measurement of parameters involving
phase angle, such as power factor, watts, and vars, which will be
covered in subsequent sections of this manual.
5.
After the connections are made, the display will indicate the ac
current flowing in the circuit.
Current Ranges
For the current input, the 918B has three different operating ranges.
Depending on the level of current applied to the input, 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.