User`s manual

13 MEASURING IMPEDANCE AND T&S PARAMETERS
13.1 INTRODUCTION
This chapter deals with impedance measurements generally before going onto the
Thiele and Small Parameters Menu description. CLIO performs impedance vs.
frequency measurements both from within the MLS and the Sinusoidal Menu. You
will find specific information in the relative Chapters. Both are relevant to what we
will now explain. Here we explain connections, principles and other topics that apply
to both menus. Differences and choice criteria are also covered.
13.2 GENERALS
Whatever the stimuli, CLIO sees a voltage at its input. Impedance is obtained by a
suitable post process, which changes depending upon how the user decides to
perform the measurement. Four methods are available. Two of them, Internal and
I Sense, were already found in the Settings Dialog, both in MLS and Sinusoidal. We
will start with these, leaving Constant Voltage and Constant Current to later on.
The last two methods derive their name from the description of what is going on
during the measurement; they were the standard before automatic computer based
Measuring Systems. Internal and I Sense are faster, requires only one
measurement, and handles the connections needed much more easily.
13.3 INTERNAL MODE
CLIO
Z
X
INPUT A
INPUT B
OUTPUT A
OUTPUT B
Figure 13.1
In principle, internal mode is very similar to Constant Current. It takes advantage
of the knowledge CLIO has of its own output level and output impedance (660 Ohm
0.1%). In fact, this value is lower than what should be used for a true Constant
Current procedure. Veterans should not worry: even if the resistor value is on the
same order of magnitude as the device you are going to measure instead of 10
times higher as usually advised, no errors occurs as CLIO is able to acquire and
evaluate the signal as a complex signal (real and imaginary) at the device
terminals. Fig.13.1 shows the connections for measuring Impedance in Internal
mode. Only one cable (XLR-to-alligators like the one in the photo) is needed,
without any other external active or passive devices. Before starting any impedance
measurement in Internal Mode remember to switch on the loop button ( or )
of the channel you are going to use.
13 MEASURING IMPEDANCE AND T&S PARAMETERS 181