Atec Agilent-16047A - Manual (Page 94)

The Concept of a Test Fixture’s Additional Error
1. System Configuration for Impedance Measurement
Very often, the system configured for impedance measurements utilizes the following components
(See figure below as well).
1. Impedance measurement instrument
2. Cables and adapter interfaces
3. Test Fixture
System configuration for impedance measurement
The Impedance measurement instrument’s characteristic measurement accuracy is defined at the
measurement port of the instrument. This means that the accuracy at the measurement port has
traceability and the measurement values are guaranteed.
In an actual measurement, there can be an extension of the measurement port with a cable or an
adapter conversion to match the test fixture’s terminal configuration. For this reason, cables and con-
version adapters are provided for connectivity with the measurement port. These cables (and
adapters) are designed with the intent to maintain high accuracy of the measurement instrument
while extending the measurement port. Most of the time, the measurement accuracy of the instru-
ment and the cable (or adapter) are specified together as a whole.
A test fixture is an accessory used to connect the DUT to the measurement instrument. Many test
fixtures are provided to adapt to various shapes and sizes. It is either connected directly to the mea-
surement port of the instrument or to the port of the extension cable or conversion adapter as
described earlier. Its structure determines the applicable frequency range and signal level. Hence, it
is necessary to use the appropriate one for the corresponding measurement conditions. In addition,
each test fixture has its own characteristic additional error, which is listed in its operational manual.
2. Measurement System Accuracy
The equation for the accuracy of a measurement system is shown below:
(Measurement Accuracy) = (Instrument’s Accuracy) + (Test Fixture’s Additional Error)
The measurement instrument’s accuracy is determined by an equation with terms, which are depen-
dent on frequency, measured impedance and signal level. By substituting the respective measure-
ment conditions into the equation, the measurement accuracy is calculated. If a cable or a conversion
adapter is used, then the specified measurement accuracy is the accuracy of the measurement instru-
ment with the cable or adapter. This combined measurement accuracy is shown in the instrument’s
operational manual.
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Appendix Additional Error