User`s manual

displayed multiplying it by the ratio between 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.
INPUT A
INPUT B
OUTPUT A
OUTPUT B
CLIO
R
S
POWER AMPLIFIER
RED
BLACK
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.
13 MEASURING IMPEDANCE AND T&S PARAMETERS 187