CLIOwin 7 PCI User's Manual - Audiomatica

etween the known resistor value and the marker reading at 1kHz. For example:
assume a known resistor value 10 Ohm, reading at 1kHz 9.3 ohm and an I Sense value
of 0.127 Ohm. Multiply 0.127 by 1.075268817 to obtain 0.13655914, input this new
value and check everything by performing a new measurement.
13.5 CONSTANT VOLTAGE & CONSTANT CURRENT
These were the standard approaches to measuring impedance with a traditional set of
instruments. We will skip further theoretical discussion and go directly on how CLIO
implements them. Both these methods require two external components, a reference
resistor of suitable and known value (where known means better than 1% tolerance)
and a power amplifier. They also require two measurements to be taken one after the
other, changing connections in between. CLIO, by means of its processing tools can
speed things up a lot but the whole procedure remains quite complicated. Whatever you
are going to use, MLS or Sinusoidal, all the measurements should be performed in Volts
(the Y Scale should be dBV).
13.5.1 CONSTANT VOLTAGE
Proceeding step by step we are going to create two files, one named “reference”, the
second named “device”. The two measurement files must have identical settings and
identical CLIO’s output level. We choose a sensing resistor, Rs, of 1 ohm at 1%
tolerance. Fig.13.11 shows connections for creating the reference file. The level you
choose now is the total measuring level.
CLIO
INPUT A
INPUT B
OUTPUT A
OUTPUT B
RS
BLACK
RED
POWER AMPLIFIER
Figure 13.11
The reference measurement is shown in Fig 13.12. As expected the output of the
amplifier appears as a straight line. Should this not be so, this would not be a problem
as the whole procedure compensates for any deviation in the frequency response. More
interesting is the absolute level. As the Rs value is small, this level appears nearly
unchanged to the speaker. We read -12dBV that translate in 250mV.
Chapter 13 - Measuring impedance and T&S parameters 163