VTI Instruments EX1000A, User Manual

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VTI Instruments Corp.
16 EX10xxA Introduction
user-defined thermocouple polynomial equations or be used as a low-noise voltmeter. Scanning
speed is programmable up to a maximum of 1 kSa/s, independent of the number of channels being
scanned. This combination of filtering and scanning speed provides the EX10xxA with the low noise
performance required for sensitive applications as well as the speed necessary to measure fast, fine-
gauge thermocouples.
For highest accuracy and stability, the EX10xxA provides an embedded isothermal input section
that is monitored by up to twelve precision thermistors (depending on model), one for every four
thermocouple channels. Moreover, it features an internal calibration source that can be used to self-
calibrate the unit upon command. This extends the unit’s high accuracy over a wide ambient
temperature range. Thermocouple accuracy is detailed in Table 1-2.
The EX10xxA is as easy-to-use as it is powerful. An integrated web page provides a convenient
way to instantly verify communications and instrument functionality, while industry standard VXI
plug & play and IVI drivers provide a familiar application programming interface to reduce
integration and program development time.
F
EATURES
Combined Thermocouple and Analog Inputs
Easily combine thermocouple and analog signals on these versatile instruments with sampling rates
up to 1 kSa/s (kilo samples per second) per channel. Each input incorporates an independent signal
conditioning path with software selectable filters for maximum flexibility. Complete channel
independence ensures data integrity regardless of sample speed or input overload conditions.
End-to-end Self-calibration
Complete end-to-end self-calibration is provided for each signal path on a programmable basis. A
highly accurate calibration source provides reference signals that are applied prior to analog filtering
and gain circuits to compensate for drift, aging, or temperature variations. Self-calibration is simple
and quick, and can be performed as often as desired.
Scalable for Synchronized High-Speed, High-Channel Count
With LXI™ Class A compliant features like a built-in Trigger Bus™ hardware trigger subsystem,
the EX10xxA supports easy integration and synchronization of multiple devices, including existing
VXI bus instrumentation.
Open Thermocouple Detection (OTD)
While the integration of the EX10xxA removes many of the reliability and connectivity problems
typically faced by system designers, they still must contend with the reliability of the sensor
connections. Fortunately, the EX10xxA aids a great deal in that regard as well. Each thermocouple
input channel generates a very small current (±7.5 nA/channel) which drives the input to an open-
circuit state if the transducer is disconnected. Implemented in this way, open transducer detection is
continuous and requires no discrete function call on the part of the user to be activated, offering
more protection than systems that only check on command, as a broken sensor can occur at any time
during testing, not just at installation. In a typical application, the OTD has no effect on the
measurement. However, many thermocouple simulators have a much higher impedance than a
thermocouple so an offset may be introduced into the reading when using a simulator. In general,
the OTD should only be active on channels that are being used with actual thermocouples.
The EX10xxA additionally offers a front panel OTD LED for each channel that illuminates upon
the recognition of a fault condition. This provides for quick and easy problem channel identification.
Moreover, to ensure that even intermittent problems are identified, the fault recognition is a latching
mechanism, retaining the information of the current acquisition sequence until a new acquisition is
initiated. Note that voltage channels do not include internal CJC thermistors, but that each voltage
D-sub includes connections for the connection of user-supplied thermistors.