VTI Instruments EX1000A, Руководство пользователя

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VTI Instruments Corp.
98 EX10xxA Programming
Resetting the device
The vtex10xxA_reset function is used to return all of the EX10xxA’s acquisition configuration
parameters to their default values. It is most commonly used to return the instrument to a known
configuration state prior to the initiation of a new test sequence. Specific affected configuration
parameters and their reset values are documented in Table 6-1. With regards to self-calibration data,
an instrument reset will clear the current self cal data and then load, if it exists, the nonvolatile self
cal data as the current self cal data. For more information on the generation and use of this data,
refer to the
Performing Self-Calibration description in this section.
NOTE An instrument reset clears the FIFO reading memory. All desired acquisition data must be retrieved
from the FIFO prior to the issuance of this function.
Performing Self-Calibration
As discussed in Self-calibration in Section 3, the measurement performance of the EX10xxA is
significantly improved through the periodic use of self-calibration. The self-calibration process
completes quickly and does not require removal of the actual input connections or the use of external
equipment, making it convenient to run often. In order to take full advantage of the self-calibration
system, it is important to understand how the self-calibration constants are generated, used, and
stored.
Self-calibration does not overwrite, modify, or take the place of the instrument’s nonvolatile
calibration constants generated by a full calibration. Instead, it generates an additional set of
calibration constants that are applied to the measurement calculation after the full calibration
constants. When self-calibration is performed, it places its calculated data in volatile memory. This
data is termed the “current self cal data” and is used automatically by the instrument. No additional
function is necessary. Because it is in volatile memory, however, it will be cleared upon an
instrument reset or power cycle. There is the ability, however, to store the current self cal data into
nonvolatile memory.
In order to perform a self-calibration, a lock on the instrument must first be acquired. For more
information on locking, refer to the
Acquiring a Lock description in this section. If self-calibration
is attempted without the acquisition of a lock, an error will be generated. The self-calibration process
is initiated with the
vtex10xxA_self_cal_init function. Once started, its percentage completion
status is accessible through the vtex10xxA_self_cal_get_status query. Other than this status check,
additional instrument driver calls should not be performed during self-calibration. Once the
completion status reaches 100%, the self-calibration process is complete.
To protect the user from performing a self-calibration while the instrument is warming up, an error
will be generated and calibration will not be performed if self-calibration is attempted before the
EX10xxA has been powered on continuously for 60 minutes. This is only a warning, however, and
it can be overridden. In general, this option should not be used, as performing self-calibration prior
to complete instrument warm-up could result in degraded measurement performance. However, it
would be appropriate to utilize the override in the case where the unit has actually been warmed up,
but has simply been subjected to a quick power cycle or reboot. Details on the override mechanism
are provided in the
vtex10xxA_self_cal_init function description in Section 6.
NOTE The self-calibration uptime requirement is in place to protect the measurement integrity of the
instrument and should only be overridden with caution. In order to ensure that the override is
intentional, it is strongly recommended that user intervention be required in the software application
to employ it.
As noted above, the self-calibration operation places its calculated data in volatile memory, termed
“current self cal data.” Once present, it can be cleared by utilizing the
vtex10xxA_self_cal_clear
function. This operation clears the volatile data, but does not affect any self cal data that is stored in
nonvolatile memory.