Promax MZ-805 Manual De Instrucciones página 73

MZ-805 L/C/R meter
The leads of a capacitor can add significant inductance at high
frequencies. Spiral wound metal film capacitors can have significant parasitic
inductance, which is why they are not used for decoupling high frequencies.
Some types of ceramic capacitors can provide excellent de-coupling, i.e. have
high capacitance with low series resistance and inductance, but can be very
lossy. Large value electrolytic capacitors can have significant inductance-this
inductance can even resonate with the capacitance at the measurement
frequencies of the MZ-805. This has the effect of showing a known high value
capacitor to have either negative capacitance or inductance.
Capacitors have two main types of parasitic resistance. Firstly there is
the physical resistance of the dielectric and dielectric losses; this is normally
specified in terms of the Dissipation Factor 'D' or loss tangent and is frequency
dependent. Secondly, there is the physical resistance of the leads and the
connections to the electrodes on the dielectric. The lead and connection
resistance are usually negligible, but on high value electrolytics, used to smooth
power supplies, it can be very important. The series resistance of such devices
is often a manufacturers specified parameter.
For most capacitors, other than high value electrolytics, the parallel
equivalent circuit will give the capacitance that matches the manufacturers data
sheet. For low loss capacitors the series and parallel equivalent capacitances
will be the same.
Electrolytic capacitors are polarity sensitive and should be connected to
the instrument correctly and bias applied. For very high value electrolytics, for
which the manufacturer specifies Equivalent Series Resistance (ESR) the
series equivalent circuit should be used.
The MZ-805 provides the means to investigate the losses of capacitors
either in terms of dissipation factor (C+D) or in terms of equivalent series or
parallel resistance (C+R).
To get maximum resolution and accuracy, low values of capacitance,
(<4nF) are best measured on the MZ-805 at 10kHz after zeroing the
capacitance with no component connected. Higher values, (>10 µ F) should be
measured at 100Hz. The instrument warns if a measurement is outside its
maximum accuracy range by flashing the units annunciator; if accuracy can be
improved by changing the measurement frequency the frequency annunciator
will also flash, see Display section.
CAUTION Always observe the recommended precautions when
loaded capacitors are manipulated, to avoid potential
damages on the equipment or users.
August 2002 Page 19