Promax MZ-805 Manual De Instrucciones página 72

The MZ-805 provides the opportunity to evaluate the series and parallel
components of resistors at 100Hz and 1kHz and 10kHz.
Some types of resistor have more prominent parasitic effects than others.
Wire wound resistors, unless they are specially wound, have more inductance
than their carbon and metal film equivalents. Even carbon film resistors have
inductance due to the inductance of the leads and the spiral cut used to trim the
resistance. There is also always capacitance between the end cap connections
- on metal film resistors it is typically around 0.25pF. This usually only becomes
significant on high value resistors or/and at high frequencies. Bifilar wound
resistors may have low inductance but the close proximity of the windings can
introduce significant capacitance-distributed along the resistance. To predict the
performance of such a component at high frequencies requires a more complex
equivalent circuit than the simple two component series or parallel circuits
discussed here. In practice the solution is to select component types to match
the frequency range of the application.
For the majority of resistors, where inductive and capacitive parasitics
are minimal, both series and parallel circuits will give identical results for
resistance.
For resistors where inductance is the significant parasitic, the series
equivalent circuit will give the value which matches the manufacturer's data-
sheet. For high value devices, capacitance can start to be significant and the
parallel equivalent circuit may be more appropriate.
Normally R+Q should be selected for resistors; the Q of a resistor will
usually be very low-especially at the low measurement frequencies used.
However if the series and parallel resistances at 10kHz differ significantly to
those at 100Hz or 1kHz, the Q will be significant. Either the inductance or
capacitance of the resistor is producing an effect. Selecting either C+R or L+Q
will quantify the parasitic capacitance or inductance.
Low value resistors can be measured at any of the three MZ-805 test
frequencies but high value resistors (>100k Ω ) are best measured on the 100Hz
range. 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.
Capacitors
All capacitors have parasitic inductance and resistance in addition to their
intended capacitance.
Page 18
MZ-805 L/C/R meter
August 2002