National Instruments NI 9211E User manual

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OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9211E
4-Channel Thermocouple Input Module
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NI 9211E Operating Instructions and Specifications 2 ni.com
This document describes how to use the National Instruments 9211E
and includes dimensions, terminal assignments, and specifications for
the NI 9211E. Visit ni.com/info and enter rdsoftwareversion
to determine which software you need for the modules you are using.
For information about installing, configuring, and programming the
system, refer to the system documentation. Visit ni.com/info and
enter cseriesdoc for information about C Series documentation.
Caution National Instruments makes no electromagnetic
compatibility (EMC) or CE marking compliance claims
for the NI 9211E. The end-product supplier is responsible
for conformity to any and all compliance requirements.
Caution The NI 9211E must be installed inside a suitable
enclosure prior to use. Hazardous voltages may be
present.
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© National Instruments Corp. 3 NI 9211E Operating Instructions and Specifications
NI 9211E Dimensions
The following figure shows the dimensions of the NI 9211E.
Figure 1. NI 9211E Dimensions in Millimeters (Inches)
73.4 (2.89)
0.0 (0.00)
26.7 (1.05) 58.4 (2.30) 66.0 (2.60)
0.0 (0.00)
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NI 9211E Operating Instructions and Specifications 4 ni.com
Connecting the NI 9211E
The NI 9211E has a 10-terminal, detachable screw-terminal
connector that provides connections for 4 thermocouple channels.
Figure 2. NI 9211E Terminal Assignments
TC0+
TC0–
TC1+
TC1–
TC2+
TC2–
TC3+
TC3–
NC
COM
0
1
2
3
4
5
6
7
8
9
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© National Instruments Corp. 5 NI 9211E Operating Instructions and Specifications
You can connect thermocouple input signals to the NI 9211E.
Connect the positive lead of the thermocouple to the TC+ terminal
and the negative lead of the thermocouple to the TC– terminal. If
you are unsure which of the thermocouple leads is positive and
which is negative, check the thermocouple documentation or the
thermocouple wire spool. If you are using shielded wiring, connect
one end of the shield to the COM terminal. The COM terminal is
internally connected to the isolated ground reference of the
module. Refer to Figure 3 for an illustration of a typical shielding
configuration.
Figure 3. Connecting a Shielded Thermocouple Input Signal to the NI 9211E
TC–
TC+
Shield
NI 9211E
COM
Thermocouple
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NI 9211E Operating Instructions and Specifications 6 ni.com
Note You must use 2-wire ferrules to create a secure
connection when connecting more than one wire to a
single terminal on the NI 9211E.
The NI 9211E channels share a common ground isolated from
other modules in the system. Each channel passes through a filter
and then a 24-bit analog-to-digital converter (ADC) samples the
channel. Each channel also has an open thermocouple detection
(OTD) circuit, which consists of a current source between the
TC+and TC– terminals. If an open thermocouple is connected to
the channel, the current source forces a full-scale voltage across the
terminals. Refer to Figure 4 for an illustration of the circuitry for
one channel of the NI 9211E.
Each channel has a resistor that produces an input impedance
between the TC+and COM terminals and between the TC– and
COM terminals. The gain and offset errors resulting from the
source impedance of connected thermocouples are negligible for
most applications. Thermocouples with a higher lead resistance
can introduce more significant errors. Refer to the Specifications
section for more information about errors resulting from source
impedance.
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© National Instruments Corp. 7 NI 9211E Operating Instructions and Specifications
Figure 4. Input Circuitry for One Channel of the NI 9211E
TC+
TC–
COM
NI 9211E
Input
Impedance
Open
Thermocouple
Detection
Current
Filtered
Differential
Amplifier
Isolated
ADC
10 MΩ
10 MΩ
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NI 9211E Operating Instructions and Specifications 8 ni.com
Temperature Measurement Accuracy
Considerations
Temperature measurement errors depend partly on the
thermocouple type, the accuracy of the thermocouple, the
temperature being measured, and the cold-junction temperature.
Refer to the Temperature Measurement Accuracy section in the
Specifications for the errors of each thermocouple type when
connected to the NI 9211E. The errors do not account for the
accuracy of the thermocouple itself.
For the best accuracy results, keep temperature gradients across
NI 9211E terminals to a minimum. Refer to the Minimizing
Thermal Gradients section for more information.
Cold-Junction Temperature Measurement Accuracy
Heat dissipated by adjacent modules or other nearby heat sources
can cause errors in thermocouple measurements by heating up the
NI 9211E terminals to a different temperature than the
cold-junction compensation sensor. The thermal gradient across
the terminals can cause the terminals of different channels to be at
different temperatures, in which case the resulting measurement
creates errors not only in absolute accuracy but also in the relative
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© National Instruments Corp. 9 NI 9211E Operating Instructions and Specifications
accuracy between channels. Refer to the Specifications section for
the cold-junction compensation accuracy specifications. Refer
to the Temperature Measurement Accuracy section in the
Specifications for the thermocouple accuracy specifications. Visit
ni.com/info and enter cjcdatascaling for more information
about isothermal errors and scaling CJC data.
Minimizing Thermal Gradients
Thermal gradients can be caused by changes in the ambient air
temperature near the front connector or by the thermocouple wire
if it conducts heat or cold directly to the terminal junctions. For the
best accuracy results, follow these guidelines for minimizing
thermal gradients:
• Use small-gauge thermocouple wire. Smaller wire transfers
less heat to or from the terminal junction.
• Run thermocouple wiring together near the screw-terminal
connector to keep the wires at the same temperature.
• Avoid running thermocouple wires near hot or cold objects.
• If you connect any extension wires to thermocouple wires,
use wires made of the same conductive material as the
thermocouple wires.
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