Promax MZ-805 Manual De Instrucciones página 75

MZ-805 L/C/R meter
Always discharge capacitors after making measurements with a DC
bias, especially at high bias voltages; failure to do so may result in
possible user injury and damage to the MZ-805 if the charged
capacitor is subsequently connected directly to the Kelvin connectors.
The MZ-805 has been designed to withstand the direct connection of
capacitors charged up to 50V DC with up to 1 Joule of stored energy
2
(½ CV ); it should not, however, be used to routinely discharge such
capacitors. Higher voltage or higher energy may result in damage to
the instrument.
Inductors
All inductors have resistive losses, parasitic capacitance and an external
coupled magnetic field. The resistive losses are the resistance equivalent to
losses in the core and the resistance of the conductive wire making up the turns
of the inductor. There is capacitance between each turn of conductor and every
other turn. The magnetic field of an inductor can extend outside the physical
package of the component.
In its simplest form the resistance can be represented as a resistor in
series with the inductance, and the capacitance as a capacitor in parallel. The
effect of an inductor's self capacitance and inductance at any given frequency
combine to produce net inductance below the resonant frequency or
capacitance above the resonant frequency.
On high value inductors, such as transformers designed to work at
50/60Hz, the self resonant frequency can be below the higher test frequencies
of the MZ-805. Above the self-resonant frequency these inductors will appear
as a lossy capacitor. Due to the distributed nature of these parasitics, the
equivalent values of the resistance and capacitance change with frequency.
The leaked magnetic field, whilst usually negligible in the case of torroids,
laminated core inductors and pot core inductors, can be significant with axial
inductors like RF chokes and ferrite rod antennae. This means that the
inductance of a device with a 'leaky' magnetic field can vary considerably
depending upon the characteristics of any conducting or magnetic material
close to the device. Any conductive material within the device's field will contain
induced currents that can in turn have the effect of reducing the apparent
inductance of the component. Conversely any ferro-magnetic material in the
immediate area of the component can have the effect of increasing the
apparent inductance. In extreme cases the inductance of a component can
appear to vary depending upon its distance above the connectors and steel
case of the MZ-805.
August 2002 Page 21