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IEEE-488 Reference

3-88

When the integration period is set using the :APERture command, the value for the :NPLCycle

command changes accordingly to reﬂect the new integration period. Conversely, if the integra-

tion period is set using the :NPLCycle command, the value for the :APERture command chang-

es accordingly.

On power-up, the instrument uses the NPLC value to determine the integration period. Thus, if

using a different power line frequency, NPLC will remain the same, but aperture may change.

Note: If line synchronization is enabled (see:LSYNc command in SYSTem subsystem), the in-

tegration period will not start until the beginning of the next power line cycle. For example, if a

reading is triggered at the positive peak of a power line cycle, the integration period will not start

until that power line cycle is completed. The integration period starts when the positive-going

sine wave crosses zero volts. See paragraph 2.12.8 for more details.

:AUTO |ONCE

[:SENSe[1]]:VOLTage[:DC]:APERture:AUTO |ONCE Control auto aperture; volts

[:SENSe[1]]:CURRent[:DC]:APERture:AUTO |ONCE Control auto aperture; amps

[:SENSe[1]:RESistance:APERture:AUTO |ONCE Control auto aperture; ohms

[:SENSe[1]]:CHARge:APERture:AUTO |ONCE Control auto aperture; coulombs

Parameters =1 or ONEnable auto aperture

0 or OFF Disable auto aperture

ONCE Enable and then disable auto aperture

Query :AUTO? Query state of auto aperture.

Description These commands are used to enable or disable auto aperture for the speciﬁed measurement

function. With auto aperture enabled, the instrument automatically optimizes the aperture value

for the present resolution setting. This is the same as selecting SET-BY-RSLN from the front

panel.

Table 2-17 provides the integration times for SET-BY-RSLN (AUTO). Note that the times are

provided as NPLC values. To convert to aperture times, use the formula in paragraph 3.19.4.

The ONCE parameter is analogous to a momentary toggle switch. When :AUTO ONCE is sent,

auto aperture turns on momentarily and then disables. While enabled, it automatically selects

the appropriate value as summarized in the tables. When auto aperture disables, the aperture re-

mains at the selected value.

:APERture:AUTO is coupled to the command that manually sets the aperture value (:APERture

<n>). When auto aperture is enabled, the parameter value for :APERture <n> changes to the au-

tomatically selected aperture value. Thus, when auto aperture is disabled, the aperture remains

at the automatically selected value. Also, a valid aperture value sent using the :APERture <n>

command disables auto aperture.

Auto aperture is also coupled to auto NPLC. Enabling or disabling auto aperture also enables or

disables auto NPLC. Also, a valid NPLC value sent using the :NPLC command disables auto

aperture.

Keithley 6517A User Manual

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