VTI Instruments EX1401, User Manual

Page: 22 / 114

VTI Instruments Corp.
22 EX1401 Introduction
EX1401 R
ACK
M
OUNT
K
IT
D
IMENSIONAL
D
IAGRAM
Note: All dimensions are in inches
M
AXIMIZING
M
EASUREMENT
P
ERFORMANCE
This section discusses tips and procedures that can help maximize the actual performance realized
with the EX1401 and aid the user in avoiding some common pitfalls associated with measurement.
Utilize self-test
Self-test should be conducted to check the working condition of measurement path, CJC thermistor
and digital control section.
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 EX1401
is designed with a CJC sensor per channel. 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 EX1401. Some
of the common sources of such thermal disturbance include steep changes in ambient temperature
and insertion of the input connector.
Select the proper filter
The EX1401 provides flexibility to choose from different types of digital filters and also facilitates
the customization of same. This provides a large combination data rates, filter types, group delays,
data latency, and decimation settings. Unless the sensor requires a higher instrument bandwidth, it
is usually recommended to use lower frequency spans with the Low Latency filter, as it provides
the greater immunity to external electrical and magnetic interference. Use of only the unfiltered
Downsampling Factor directly (without any filter) is not recommended, since the spectral purity of
the output is lower than with filtered decimation, but pairing it with a filter can achieve very low
sample rates with good performance. Choice of the proper filter must be optimized for a given
application, and all filters are not suited to all applications.