Specifications

4.3 Compensation

Compensation is also called correction and reduces the effects of the error sources existing between

the DUT and the instrument’s calibration plane. Compensation, however, can not always completely

remove the error. Thus, the measurement accuracy obtained after compensation is not as good as

that obtained at the calibration plane. Compensation is not the same as calibration and can not

replace calibration. Compensation data is obtained by measuring the test fixture residuals. The

accuracy of compensation data depends on the calibration accuracy of the instrument, so compensa-

tion must be performed after calibration has been completed.

Compensation improves the effective measurement accuracy when a test fixture, test leads, or an

additional measurement accessory (such as a component scanner) is used with the instrument. The

following paragraphs describe three commonly used compensation techniques:

• Offset compensation

• Open/short compensation

• Open/short/load compensation

Note: The open/short/load compensation for the auto-balancing bridge instrument (described in

Section 4.3.3) is not applied to RF-IV instruments because the compensation theory for the

RF-IV method is different from that for the auto-balancing bridge method.

4.3.1 Offset compensation

When a measurement is affected by only a single component of the residuals, the effective value can

be corrected by simply subtracting the error value from the measured value. For example, in the

case of the low value capacitance measurement shown in Figure 4-3, the stray capacitance (Co),

paralleled with the DUT’s capacitance (Cx) is significant to the measurement and can be removed by

subtracting the stray capacitance value from the measured capacitance value (Cxm). The stray

capacitance value is obtained with the measurement terminals left open (Com).

Figure 4-3. Offset compensation

LCR meter

DUT

: Corrected capacitance of the DUT

: Measured capacitance of the DUT

: Stray capacitance

: Measured stray capacitance

LCR meter

= C

+ C

= C

- C

4-3