ETS-Lindgren HI-3604, Руководство пользователя

Страница: 8 / 45

8
www.ets-lindgren.com
Surrounding the circular displacement current sensing disks is a coil
consisting of several hundred turns of fine gage wire. When placed in
an alternating magnetic field, a current is induced in the coil which is
proportional to the strength of the applied magnetic field. Magnetic field
strength is then determined by measuring the voltage developed
across the terminals of the coil. While an unterminated loop will provide
an output which is directly proportional to the frequency of the
magnetic field, the HI-3604 employs electronic compensation circuitry
which results in a tailored frequency response that is flat in the
frequency range of importance to power frequency measurements.
This feature permits the HI-3604 to be used in environments having
significant harmonic content and yield accurate measures of the
resultant fields. Broadband response is required when measuring fields
having significant harmonic distortion such as may occur with electrical
machinery.
The outputs of both field transducers are measured with a true RMS
detector. True RMS detection offers accurate evaluation of fields
having a variety of waveforms, including non-sinusoidal waveforms.
Thus, whether the field being measured is produced by a near pure
sine wave source, like an electric power transmission line, or a highly
non-sinusoidal source, like a solid state light dimmer, the HI-3604 will
yield consistent measures of the RMS field strengths.
Instrument accuracy is derived from a field calibration using a one
meter diameter pair of Helmholtz coils for establishing an accurately
known magnetic field strength, and a pair of parallel one-meter square
aluminum plates separated by 30 cm for creating known electric field
strength. In the case of the Helmholtz coils, a precisely controlled and
measured sinusoidal current is driven through the coils and, based on
the dimensions of the coils, the magnetic field strength in units of
milligauss (mG) is calculated. For electric fields, a sinusoidal voltage
impressed across the two parallel plate electrodes is directly measured
and used to calculate the electric field strength by dividing the applied
voltage by the plate spacing to obtain field strength in units of volts per
meter (V/m). In each case, both currents and voltages in the calibration
set-ups are determined with a true RMS detector.