VTI Instruments EX1000A, Руководство пользователя

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VTI Instruments Corp.
62 EX10xxA Triggering
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CALIBRATION
In order to deliver high measurement accuracy over a wide ambient operating temperature range,
the EX10xxA provides the ability to perform an instrument self-calibration. During self-calibration,
the input signal conditioning paths are disconnected from the input jacks and connected instead to
a calibration bus that is driven by an internal calibration source. Through measurement of the
conditioning paths at multiple calibration source points, software compensation for circuitry drift
since the last full calibration is conducted. Once self-calibration is performed, the
Thermocouple
Accuracy in Table 1-2 is valid for 7 days and over a ±5 ºC ambient temperature change. Note,
however, that the unit must still undergo a full calibration at least once a year, regardless of the use
of self-calibration.
Self-calibration should be conducted as often as practical, especially if the ambient environment has
changed significantly since the previous calibration. However, fast ambient environmental changes
should ideally be followed by a period of thermal stabilization before conducting self-calibration to
allow the internal circuitry to stabilize to a new thermal operating condition. The self-calibration
process completes quickly and does not require removal of the actual input connections, making it
convenient to run often.
Similarly, self-calibration should only be performed after the EX10xxA 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 it can be overridden by repeating the calibration function call. 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
resets 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 EX10xxA 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 EX10xxA, resulting in significant performance improvement.
However, it cannot compensate or correct for cold junction thermal stabilization errors that are
created by excessive external sources of heat/cold or a population change of input connectors that
is not followed by a thermal equilibrium delay. Similarly, any error created from the resistive drop
of very long thermocouple wires is outside of the calibration loop and is not eliminated. For more
details, see
Maximizing Measurement Performance
Self-calibration operations can be performed through the embedded web page or instrument driver
interfaces. For web page operations, see
Self-calibration in Section 4. For programming operations,
see Performing Self-Calibration in Section 5.
NOTE EX1044 system requires hard reboot after self-calibration process so that instrument will be
calibrated values gets loaded upon reboot.