VTI Instruments EX1000A, User Manual

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EX10xxA Introduction 31
M
AXIMIZING
M
EASUREMENT
P
ERFORMANCE
This section discusses tips and procedures that can help maximize the actual performance realized
with the EX10xxA and aid the user in avoiding some common pitfalls associated with thermocouple
measurement.
Utilize 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.
The self-calibration process completes quickly and does not require removal of the actual input
connections, making it convenient to run often.
NOTE Self calibration is not applicable for RX10xx since during factory calibration process each
instrument will be calibrated in precise manner and calibrated data gets stored in the instrument
memory. The instrument has to be sent to factory to perform subsequent calibration after the initial
calibration date is expired.
Refer below section for Dynamic Calibration in RX1032
Dynamic Calibration in RX1032
The dynamic calibration should be conducted to calibrate the measurement drift due to the
temperature change. For every measurement scan, the values are adjusted based on the system
internal temperature.

The initial calculated Voltage and Temperature coefficients are stored into the RX1032
system.

At every measurement the measured values are calibrated dynamically using the stored
coefficients.

Based on the present temperature of the system, the values are calibrated and reported.
Utilize self-test
Self-test should be conducted to check the working condition of CJC thermistor. Generally it should
be followed after self-calibration However at least 30 minutes warm up time should be sufficient
enough before conducting self-test. The self-test process takes at least 2 minutes for completion and
does not require removal of the actual input connections, making it convenient to run often. After
every self-test operation the unit should be stabilized for at least 30 minutes.
Allow for cold junction thermal stabilization
The performance of any thermocouple measurement instrument is largely determined by the
stability of the cold junction sensing mechanism. For maximum accuracy and stability, the
EX10xxA is designed with a significant thermal mass that connects the input connectors to the cold
junction sensing element. However, while this lowers the sensitivity to thermal disturbances,
transient measurement errors are still possible under certain operating conditions. Awareness of
these conditions will help achieve the maximum performance from the EX10xxA.
Step change in ambient temperature
If the EX10xxA is subjected to a significant ambient temperature change over a short period of time,
a transient measurement error will occur due to the inherent thermal time constant differences
between the thermal mass and the actual cold junction made between the EX10xxA input connector
and the type-specific thermocouple connector. The magnitude of the error will be directly
proportional to the rate of change of the ambient temperature. Because the actual cold junction is
more closely tied to the external ambient conditions than the internal thermal mass, it will follow
the ambient temperature change to a slightly better extent than the thermal mass. Consequently,
when subjected to a drastic rise in ambient temperature, the actual cold junction will rise in