SRS Labs SR715, Руководство пользователя

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OPERATION
2-16
OPEN and SHORT CIRCUIT OR NULL CALIBRATION
Compensation of stray impedances is performed by open and short circuit or fixture null calibration. This
corrects for lead impedance, and fixture, cable and other stray capacitance. Null calibration corrects for all
frequencies and all ranges - it is not necessary to re-calibrate for changes in frequency. Null calibration should
be performed after any change in fixture configuration or for changes in the drive amplitude. For critical
measurements, null cal should be performed frequently, possibly several times a day. The open and short
circuit values are stored with the [Store] and [Recall] keys, allowing null calibration data to be saved for
different fixture configurations.
The Null Calibration procedure is in the CAL menu. Press the [Calibrate] key until the message 'nuLL cAL'
appears on the display. Press the [ENTER] key and the message will change to 'Short cAL'. Place a wire of
between 26 to 16 AWG (0.02" to 0.05" or 0.51 to 1.30 mm dia.) in the fixture. Press the [ENTER] key and
move hands and any miscellaneous objects away from the fixture. When the short circuit cal is finished, the
'oPEn cAL' message will be displayed. Remove the shorting wire, press [ENTER] and again move your hands
away from the fixture. When the unit has finished, the message 'cAL donE' will be displayed. Use the [Display]
key return to the desired display.
Suggestions for Calibration
It is always best to perform the null calibration in the same configuration that measurements will be made. This
will ensure that stray impedances will be cancelled out as completely as possible. Also, keep any objects away
from the fixture that will not be present during measurements, for example hands or pieces of metal. (To
observe the effect your hand has on impedances, place a small capacitor, ~10pF, in the fixture and observe
the change in measured capacitance as you move your hand closer to the fixture. This is due to your hand
disturbing the electric fields around the fixture). For high impedance measurements, the open circuit null will
be more accurate if the fixture contacts are clean. A piece of paper (the coarser the better) slid back and forth
between the contacts will clean them (if they are not too dirty).
RADIAL FIXTURE Use a "U" shaped piece of copper wire, 26 to 16 AWG (0.02 to 0.05" or 0.51 to
1.30 mm dia.), 2"-3" long (50-80mm) for the shorting wire. Insert the shorting wire
in both sides of the fixture at about the same places that the component leads will
be inserted.
AXIAL FIXTURE ADAPTER Place the axial adapters in the desired locations on the fixture. For the shorting
wire, use a straight piece of wire or a lead (26-16 AWG) that fits in the contacts in
the same fashion as the parts to be measured do.
KELVIN CLIPS It is more difficult to get an accurate null calibration with the Kelvin clips than with
a fixture, since their physical configuration is less controlled. As always, place
them as close to the measurement configuration as possible while making null
measurements. For the shorting measurement DO NOT connect the two clips
together. Connect the two clips to the same side of a DUT, ensuring the same
contact resistance that as in actual measurements. For the open measurements,
leave one clip attached to the DUT and position the other at about the same