VTI Instruments EX1629, Руководство пользователя

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VTI Instruments Corp.
56 EX1629 Basic Operation
Similarly, self-calibration should only be performed after the EX1629 has been allowed to warm
up from a cold start for at least 60 minutes. To protect the user, the instrument will return a
warning if self-calibration is initiated prior to the completion of this warm-up time. However, it is
only a warning and can be overridden by repeating the calibration function. An override would be
completely acceptable, for example, in cases where a) the unit is already fully warmed-up and is
quickly moved from one physical location to another or b) instrument line power is briefly lost
due to a facility power outage.
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. By default, self-calibration data is volatile, meaning that it is not saved through
instrument reboots or power cycles. This ensures that the instrument always initializes with
calibration constants generated by a full calibration. This feature is particularly important when the
instrument is being shared among multiple users. Each user is consequently sheltered from the
actions of others.
Despite having the ability to conduct self-calibration at any time, there may be user applications
that require the use of self-calibration, but demand that it create nonvolatile data. The EX1629
supports that operation as well. Once self-calibration is performed, the data can be stored to
nonvolatile memory through a separate function. Similarly, previously stored self-calibration data
can be loaded or cleared from nonvolatile memory.
Self-calibration offers a convenient way to mitigate the effects of time and temperature on the
signal conditioning circuitry of the EX1629, resulting in significant performance improvement.
However, it cannot compensate or correct for potential drift errors caused by an excitation source
change that is not followed by a thermal equilibrium delay. Similarly, any error caused by lead
wire desensitization is outside of the calibration loop and is not eliminated. Finally, the use of self-
calibration does not remove the necessity of excitation source measurement to achieve stated
accuracies. For more details, see
Maximizing Measurement Performance in Section 1.
L
OCKING
By default, the EX1629 allows unrestricted operation from multiple hosts. While this offers a high
level of user flexibility, there are instances where protected operation is desirable, if not required.
For these applications, the EX1629 can be “locked,” meaning that it will accept function calls
from only the host IP address that issued the lock function call. With the EX1629 in this mode,
other host connections that attempt function calls will be denied.
By design, the locking mechanism is able to be overridden by a secondary host that issues a break
lock function. Thus, the lock provides a warning to other users that the unit is in a protected
operation state, but not absolute security. This allows for instrument recovery if the host or
application should become disabled. Self-calibration requires the acquisition of a lock prior to its
initiation.
C
ONFIDENCE
S
CAN
L
IST
C
ONFIGURATION
The Confidence Measurement System allows several signals within a bridge to be measured, in
addition to the voltage across the bridge (main input channels), including the excitation voltages
and currents. The confidence measurement system is configured by a scanlist, analogous to the
main input channel scanlist, except that, in the case of the confidence measurement system, the
measurements are actually taken sequentially (scanned) by a number of ADCs, whereas the main
input channels each have a dedicated ADC.