Specifications

Figure 4-9. Actual open/short load measurement example
4.3.5 Application limit for open, short, and load compensations
When the residuals are too significant compared to the DUT’s impedance value, compensation may
not work properly. For example, if the measured short impedance (Zsm) is about the same as the
DUT’s impedance, total measurement error will be doubled. The following are typical criteria for
this limitation:
(1) Measured open impedance (Zom) must be more than 100 times the measured impedance of the DUT.
(2) Measured short impedance (Zsm) should be less than 1/100 of the measured impedance of the
DUT.
4.4 Measurement error caused by contact resistance
Any contact resistance existing between the DUT electrodes and the contact electrodes of the test
fixture or test station will result in measurement error. The effects of the contact resistance are dif-
ferent for the DUT connection methods, 2T and 4T. In the case of a 2T connection, the contact
resistance is added to the DUT impedance in series and produces a positive error in the dissipation
factor (D) reading (see Figure 4-10 (a).) In the case of a 4T connection, contact resistances Rhc, Rhp,
Rlc, and Rlp exist as shown in Figure 4-10 (b.) The effects of the contact resistance differ depending
on the terminals. Rhc decreases the test signal level applied to the DUT, but it does not directly pro-
duce measurement error. Rlp may cause the auto-balancing bridge to be unstable, but generally its
effect is negligible. Rhp and Chp (distributed capacitance of the coaxial test cable) form a low-pass
filter, which causes attenuation and phase shift of the Hp input signal, producing measurement
error. Rlc and Clc also form a low-pass filter and cause an error in measured DUT current
and phase angle. Since the resultant dissipation factor error is proportional to –ωRhp × Chp and
–ωRlc × Clc, the D error is a negative value and increases with frequency. This error becomes signifi-
cant when the 4T connection method is used in high frequency measurements. The 4T connection
gives a constant D error (that is determined by the contact resistance and test lead capacitance
only) while the error of the 2T connection varies depending on the DUT’s value (Figure 4-10 (c).)
The 4T connection provides minimal error only when the effects of contact resistance and test lead
capacitance are negligible (mainly at low frequencies.)
4-9
Step 1: Using a direct-connected test
fixture, measure the load.
Step 2: Measure load compensation data using
fixture to be compensated.