VTI Instruments EX1401, User Manual

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EX1401 Basic Operation 39
exceeding ±10V level will result in measurements reported as the floating-point representation of
NaN (Not a Number). The instrument will be damaged permanently, if differential voltage across
any channel, exceeds ±100 V
peak
.
NOTE The application of differential voltages beyond ±100 Vpeak may permanently damage the EX1401.
All inputs are protected from EMI using 100pF feed through capacitors to chassis ground. Also they
are protected from accidental electro static discharges (ESD).
C
OLD
J
UNCTION
C
OMPENSATION
(CJC)
For highest accuracy and stability, the EX1401 provides embedded isothermal input sections that
are monitored by high precision thermistors, one for each thermocouple input channel. Although
internal compensation capabilities are present, it is still possible to disable this feature and define
CJC temperatures externally. To ensure that CJC information is current and time correlated with the
input channels, CJC channel measurements are synchronized with input sampling clock, providing
a maximum time separation of less than 200 ms between the input channel measurement and its
associated CJC measurement. Internal CJC channels are measured via a separate 16-bit ADC, which
is synchronously clocked at 10 SPS to 20 SPS.
NOTE The health of internal CJC channels is verified during the instrument self-test.
The user has configuration control over the reporting of the measured CJC data. This control only
affects the display of their data, not the actual measurement of them. They are updated with every
scan, regardless of their reporting status.
The EX1401 also accommodates the use of an external cold junction that is maintained and
measured by the user. In this application, the cold junction temperature in ºC is entered into the
EX1401 and enabled on a per channel basis. That is, the use of internal and user-defined CJC inputs
can be mixed throughout the unit.
The default selections are:
•
CJC reporting is disabled
•
User-defined CJC temperatures are 0.0
•
User-defined CJC temperatures are disabled for all channels
T
EMPERATURE
U
NITS
The EX1401 can output its temperature data with units of ºC or ºF. This is controlled on a global
basis, such that all input channels are configured with one setting. This selection applies to input
channel data only. Input channels configured for an EU conversion of voltage are unaffected by this
setting.
The default selection is °C.
S
AMPLING
R
ATE
/F
ILTERS
/N
OISE
F
LOOR
The EX1401 supports a large range of sampling rates, due to its flexible ADC sampling clock and
programmable digital filters. Sampling rate is dependent on the decimation filters performance
expectation, and latency of first data that can be tolerated by your application. Figure 3-1 represents
the general architecture of the EX1401 ADC and filter scheme.