National Instruments SCC-TC Series User manual

USER GUIDE
SCC-TC Series Thermocouple
Input Modules
The SCC-TC Series thermocouple input modules, SCC-TC01 and
SCC-TC02, accept input signals from B-, E-, J-, K-, N-, R-, S-, and T-type
thermocouples. Each module contains thermistor circuitry powered by
2.5 V, to compensate for cold-junction effects and can detect open
thermocouple circuits. Each module has one thermocouple input channel,
which consists of a gain of 100 differential amplifier and a dual-pole 2 Hz
filter.
Note Alternatively, you can use the SCC-TC02 as a 2 Hz lowpass bandwidth ±100 mV
input module.
Conventions
The following conventions are used in this guide:
»The »symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash. When this symbol is marked on
the product, refer to the Read Me First: Safety and Radio-Frequency
Interference document, shipped with the product, for precautions to take.
When symbol is marked on a product, it denotes a warning advising you to
take precautions to avoid electrical shock.
When symbol is marked on a product, it denotes a component that may be
hot. Touching this component may result in bodily injury.

SCC-TC Series Thermocouple Input Modules User Guide 2 ni.com
bold Bold text denotes items that you must select in the software, such as menu
items and dialog box options. Bold text also denotes parameter names.
italic Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. This font also denotes text that is a placeholder for a word
or value that you must supply.
monospace Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames, and extensions.
SC-2345 SC-2345 refers to both the SC-2345 connector block and the SC-2345
configurable connector.
SCC SCC refers to any SCC series signal conditioning module.

©National Instruments Corporation 3 SCC-TC Series Thermocouple Input Modules User Guide
What You Need to Get Started
To set up and use the SCC-TC0X, you need the following items:
❑SC-2345/2350 with one of the following:
– SCC-PWR01
– SCC-PWR02 and the PS01 power supply
– SCC-PWR03 (requires a 7 to 42 VDC power supply, not included)
❑One or more SCC-TC0Xmodules
❑SCC-TC Series Thermocouple Input Modules User Guide
❑Read Me First: Safety and Radio-Frequency Interference
❑SC-2345/2350 User Manual, available at ni.com
❑SCC Quick Start Guide, available at ni.com
❑SC-2345 Quick Reference Label
❑68-pin E Series DAQ device, documentation, and 68-pin cable
❑1/8 in. flathead screwdriver
❑Numbers 1 and 2 Phillips screwdrivers
❑Wire insulation strippers
❑NI-DAQ (current version) for Windows 2000/NT/XP/Me
Note Software scaling of measurements is not supported on the Macintosh operating
system. Refer to the Scaling Voltage Measurements section for more information about
measurement scaling.

SCC-TC Series Thermocouple Input Modules User Guide 4 ni.com
Device Specific Information
Note For general SCC module installation and signal connection information, and
information about the SC-2350 carrier, refer to the SCC Quick Start Guide, available
for download at ni.com/manuals.
Installing the Module
Caution Refer to the Read Me First: Safety and Radio-Frequency Interference document
before removing equipment covers or connecting/disconnecting any signal wires.
You can plug the SCC-TC0Xinto any analog input socket on the SC-2345.
The socket you select determines which E Series DAQ device channels
receive the SCC-TC0Xsignals.
For single-stage input conditioning, plug the SCC-TC0Xinto any socket
J(X+1), where Xis 0 to 7, and connect the input signals to the module as
described in the Connecting the Input Signals section.
If you use the SCC-TC0Xin a dual-stage configuration, the SCC-TC0X
must be the first-stage module. Plug it into any socket J(X+9) and plug the
second-stage SCC into socket J(X+1), where Xis 0 to 7. Connect the input
signals to SCC-TC0Xas described in the Connecting the Input Signals
section. The SC-2345 connects the output signals of the first-stage SCC to
the inputs of the second-stage SCC. An example of dual-stage conditioning
in an SCC-TC0Xfollowed by an SCC-LP01 lowpass filter module.
Sockets J9 to J16 also are available for digital input/output (DIO)
conditioning or control. Refer to the SC-2345 User Manual for more
information on configuring, connecting, and installing SCC modules
Note SCC-TC0Xdual-stage configuration is only available in NI-DAQ 7.1 or later.

©National Instruments Corporation 5 SCC-TC Series Thermocouple Input Modules User Guide
Connecting the Input Signals
Note The signal names have changed. Refer to ni.com/info and enter rdtntg to
confirm the signal names.
The SCC-TC01 has a two-prong uncompensated thermocouple
miniconnector that accepts any miniature or subminiature two-prong
male thermocouple connector. The SCC-TC02 has a three-position
screw-terminal connector that accepts 28 to 16 AWG thermocouple wires.
The screw-terminal connector provides a ground connection for shielded
thermocouples. Otherwise, the two modules function identically.
To use an SCC-TC01, plug the male thermocouple connector into the
module.
The SCC-TC02 accepts up to three signals: TC+, TC–, and GND. TC+is
the positive thermocouple lead and TC– is the negative thermocouple lead.1
The GND terminal connects to AI GND on the E Series DAQ device.
The SCC-TC0Xhas a 10 MΩbias resistor connected from the negative
thermocouple input to ground. This resistor allows the thermocouple to be
ground-referenced or floating without requiring external bias resistors
connected to ground.
1 For ANSI color-coded J-type thermocouples, the red wire is negative and the white wire is positive. Refer to the thermocouple
data sheet if possible. You can find information about other color-coding schemes in the NI KnowledgeBase at ni.com/
support.

SCC-TC Series Thermocouple Input Modules User Guide 6 ni.com
The amplified thermocouple signal and cold-junction sensor signal
are measured by E Series DAQ device channel Xand channel X+8
respectively, where Xis 0 to 7 depending on where you plug the
SCC-TC0X. Refer to Figure 1 for SCC-TC0Xsignal connections.
Figure 1. SCC-TC0XSignal Connections
For more information about how to configure the SCC-TC module using
NI-DAQmx, refer to the SCC Quick Start Guide.
Thermocouple
Source
AI ( X )
AI (
X +8)
SCC-TC0
X
E Series
DAQ Device
+
–
4.75 kΩ
1%
5 kΩ
0.1%
10 kΩ
10 kΩ
2.5 kΩ
+
5 kΩ
at 25oC
10 MΩ
10 MΩ
10 µF
16 V 0.1 µF
0.1 µF
-to
Ref 5 V
Ref 5 V
LM 4040
2.5 V
0.1%
2-Pole Filter/
Buffer Stage
Offset
Calibrator
AI SENSE
TC+
GND
(SCC-TC02
only)
TC-
AI GND
+
–

©National Instruments Corporation 7 SCC-TC Series Thermocouple Input Modules User Guide
Using the TC0X
Scaling Voltage Measurements
Note NI-DAQ includes thermocouple and thermistor conversion utilities that implement
the conversions required in steps 3 and 5 of the following procedure. Refer to your
software documentation for more information on these utilities.
Your software environment may return only voltage measurements from
E Series DAQ devices. If so, you must convert voltage measurements to
temperature measurements. To make this conversion, complete the
following steps:
1. Measure the thermocouple voltage.
a. Read the thermocouple channel on the E Series DAQ device
VESERIES [CH(X)].
b. Calculate the thermocouple voltage by using the following
formula:
where
VTC is thermocouple voltage.
VESERIES is E Series DAQ device voltage.
This step provides proper scaling for the thermocouple amplifier in the
SCC-TC0X.
2. Measure the reference-junction (cold-junction) temperature.
a. Read the thermistor voltage [AI (X+8)].
b. Convert the thermistor voltage to cold-junction temperature using
the formula in the Cold-Junction Sensor section.
3. Calculate the cold-junction compensation voltage by converting the
cold-junction temperature from step 2 to a thermocouple voltage. Use
the polynomial expressions applicable to the type of thermocouple you
are using.
4. Apply the cold-junction compensation to the thermocouple reading
by adding the cold-junction compensation voltage from step 3 to VTC.
5. Calculate the thermocouple temperature by converting the voltage
result from step 4 to a temperature. Use the polynomial expressions
applicable to the type of thermocouple you are using. This calculation
gives you a linearized temperature measurement.
Note Polynomials are from NIST Monograph 175.
VTC
VESERIES
100
---------------------=

SCC-TC Series Thermocouple Input Modules User Guide 8 ni.com
Uncompensated Connectors and Accuracy
If you are using an SCC-TC02 with an uncompensated SCC panelette,
temperature gradients between the module and the junctions on the
panelette affect the accuracy of your measurements.
Detecting Open Thermocouples
The SCC-TC0Xcontains a 10 MΩpull-up resistor that connects to
+5 V to detect open thermocouples. To determine if you have an open
thermocouple, check whether the corresponding E Series DAQ device
channel is saturated. The pull-up and bias resistors saturate the channel by
applying +2.5 V at the input of an open channel. This results in saturation
to either the positive or negative rails of the E Series DAQ device (±10 V).
Errors Due to Open-Thermocouple Detection Circuitry
The open-thermocouple detection circuitry can cause measurement errors.
These errors are the results of common-mode voltage at the input of the
SCC and current leakage into the signal leads. The 10 MΩbias resistor in
the SCC-TC0Xcauses this error to be negligible. With the 10 MΩbias
resistor connected to ground and the 10 MΩpull-up resistor connected to
+5 VDC, a current leakage of approximately 0.25 µA (5 V/20 MΩ) flows
into the unbroken floating thermocouple. Long thermocouple leads result
in larger voltage drops due to lead resistance.
For example, if you have a 24 AWG J-type thermocouple that is 20 ft long,
a voltage drop of approximately
4 µV = (0.145 Ω/ft +0.658 Ω/ft) ×20 ft ×0.25 µA
can develop in the thermocouple, which corresponds to an error of 0.09 °C.
With 10 MΩpull-up and bias resistors, a common-mode voltage of
+2.5 VDC develops if the thermocouple is floating. The common-mode
rejection of the SCC-TC0Xis sufficiently high, which results in the offset
voltage being negligible in most applications.
If your application demands extremely high accuracy, you can eliminate
these errors by calibrating the system. Refer to the Calibrating System
Offsets section for more information.

©National Instruments Corporation 9 SCC-TC Series Thermocouple Input Modules User Guide
Cold-Junction Sensor
The cold-junction sensor voltage output varies from 1.91 to 0.58 V over a
0 to 55 °C temperature range.
Note NI-DAQ includes thermistor conversion utilities that implement the equations listed
below. Refer to your software documentation for more information on these utilities.
You can use the following formulas to convert the cold-junction sensor
voltage to cold-junction temperature:
where TKis the temperature in kelvin.
where
a= 1.295361 ×10–3
b= 2.343159 ×10–4
c= 1.018703 ×10–7
RTis the resistance of the thermistor in ohms.
where VTEMPOUT is the output voltage of the cold-junction sensor.
where T(°F) and T(°C) are the temperature readings in degrees Fahrenheit
and Celsius, respectively.
Note VTEMPOUT varies from 1.91 V (at 0 °C) to 0.58 V (at 55 °C). For best resolution, use
the maximum gain for this range on the analog input channel.
For the cold-junction sensor measurement accuracy, refer to the
Specifications section.
For more information about how to configure the SCC-TC using
NI-DAQmx, refer to the SCC Quick Start Guide.
T°C() TK273.15–=
TK
1
ab Rln T
()cRln T ()
3
++[]
--------------------------------------------------------------=
RT5000
VTEMPOUT
2.5 VTEMPOUT –
--------------------------------------


,=
T°F() T°C()]9[
5
------------------------32+=

SCC-TC Series Thermocouple Input Modules User Guide 10 ni.com
Calibrating System Offsets
To calibrate the offset voltage of the SCC-TC0Xin the system using the
E Series DAQ device, complete the following steps. The E Series DAQ
device must be on for 30 minutes before you calibrate the offset voltage.
1. Select the desired channel and gain on the E Series DAQ device.
2. Short the inputs on the SCC-TC0Xscrew terminals or miniplug.
3. While acquiring data on the selected channel, use a screwdriver to
adjust the potentiometer protruding through the top of the module until
you read 0 VDC.
Calibrating the SCC-TC0XUsing a Thermocouple
Calibrator
To calibrate the system using a thermocouple calibrator, complete the
following steps:
1. Make sure that the thermocouple connections at both the SCC and the
thermocouple calibrator are at the same temperature.
2. Connect the thermocouple calibrator to the SCC-TC0X. For best
results, use thermocouple wire of the same length and type that you
use in the thermocouple.
3. Set the thermocouple calibrator to the required calibration
temperature.
4. Measure the calibrator voltage using the SCC-TC0X.
5. Convert the measured calibrator voltage to a temperature measurement
as described in the Scaling Voltage Measurements section.
6. Adjust the potentiometer on the top of the SCC-TC0Xso that the
measured temperature is equal to the calibration temperature.