Specifications

65
dataTec ▪ Ferdinand-Lassalle-Str. 52 ▪ 72770 Reutlingen ▪ Tel. 07121 / 51 50 50 ▪ Fax 07121 / 51 50 10 ▪ [e-mail] ▪ www.datatec.de
The Concept of a Test Fixture’s Additional Error
1. System Configuration for Impedance Measurement
Frequently the system configured for impedance measurements uses the following components.
1. Impedance measurement instrument
2. Cables and adapter interfaces
3. Test fixture
System configuration for impedance measurement
The impedance measurement instrument’s accuracy is defined at the measurement port of the instrument. This means
that the accuracy at the measurement port is guaranteed and has calibration traceability.
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 conversion adapters are provided for connec-
tivity with the measurement port. These cables (and adapters) are designed to maintain high accuracy of the measure-
ment 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 of DUTs. A test fixture is either connected directly to the measurement port of the
instrument, or to the port of the extension cable or conversion adapter, as described earlier. The test fixture's structure
determines the applicable frequency and impedance ranges. Hence, it is necessary to use the appropriate test fixture
for the desired measurement conditions. In addition, each test fixture has its own inherent characteristic error, which is
detailed in its operational manual.
2. Measurement System Accuracy
The equation for the accuracy of a measurement system is:
(Measurement accuracy) = (Instrument’s accuracy) + (Test fixture’s error)
The measurement instrument’s accuracy is determined by an equation with terms that are dependent on frequency,
measured impedance, signal level, and measurement time mode. By substituting the respective measurement condi-
tions 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 instrument with the cable or adapter. This com-
bined measurement accuracy is shown in the instrument’s operational manual.
65
Appendix Additional Error