Omega OM-USB-TC-AI User manual

Servicing North America:
U.S.A.: Omega Engineering, Inc., One Omega Drive, P.O. Box 4047
Stamford, CT 06907-0047 USA
Toll-Free: 1-800-826-6342 (USA & Canada only)
Customer Service: 1-800-622-2378 (USA & Canada only)
Engineering Service: 1-800-872-9436 (USA & Canada only)
Tel: [phone] Fax: [phone]
e-mail: [email protected]
For Other Locations Visit omega.com/worldwide
omega.com [email protected]
The information contained in this document is believed to be correct, but OMEGA accepts no liability for any errors it contains, and reserves
the right to alter specifications without notice.
WARNING: These products are not designed for use in, and should not be used for, human applications.

2
Table of Contents
Preface
About this User’s Guide .......................................................................................................................4
What you will learn from this user’s guide.........................................................................................................4
Conventions in this user’s guide.........................................................................................................................4
Where to find more information.........................................................................................................................4
Chapter 1
Introducing the OM-USB-TC-AI............................................................................................................5
Overview: OM-USB-TC-AI features .................................................................................................................5
OM-USB-TC-AI block diagram.........................................................................................................................6
Software features................................................................................................................................................6
Connecting a OM-USB-TC-AI to your computer is easy...................................................................................7
Chapter 2
Installing the OM-USB-TC-AI................................................................................................................8
What comes with your OM-USB-TC-AI shipment? ..........................................................................................8
Hardware .......................................................................................................................................................................... 8
Documentation.................................................................................................................................................................. 8
Unpacking the OM-USB-TC-AI ........................................................................................................................8
Installing the software ........................................................................................................................................9
Installing the OM-USB-TC-AI...........................................................................................................................9
Configuring the OM-USB-TC-AI ......................................................................................................................9
Calibrating the OM-USB-TC-AI........................................................................................................................9
Chapter 3
Signal I/O Connections.......................................................................................................................10
Screw terminal pinout.......................................................................................................................................10
Voltage input terminals (±V0H/V0L to ±V3H/V3L).......................................................................................................11
Thermocouple input terminals (T0H/T0L to T3H/T3L) ..................................................................................................11
Ground terminals (GND).................................................................................................................................................12
Power terminals (+5V).....................................................................................................................................................12
Digital terminals (DIO0 to DIO7)....................................................................................................................................12
Counter terminal (CTR)...................................................................................................................................................12
CJC sensor.......................................................................................................................................................................12
Thermocouple connections...............................................................................................................................12
Wiring configuration........................................................................................................................................................12
Digital I/O connections.....................................................................................................................................13
Configuring the DIO channels to generate alarms ...........................................................................................................14
Chapter 4
Functional Details ...............................................................................................................................15
Thermocouple measurements ...........................................................................................................................15
Cold junction compensation (CJC)..................................................................................................................................15
Data linearization.............................................................................................................................................................15
Open-thermocouple detection (OTD) ..............................................................................................................................15
USB connector..................................................................................................................................................15
LEDs.................................................................................................................................................................15
Power................................................................................................................................................................16
Chapter 5
Specifications......................................................................................................................................17
Analog input.....................................................................................................................................................17
Channel configurations.....................................................................................................................................18

OM-USB-TC-AI User's Guide
3
Compatible sensors: T0x toT3x.......................................................................................................................................18
Accuracy...........................................................................................................................................................19
Thermocouple measurement accuracy: T0x to T3x.........................................................................................................19
Absolute accuracy: V0x-V3x...........................................................................................................................................20
Settling time: V0x-V3x....................................................................................................................................................20
Analog input calibration...................................................................................................................................21
Throughput rate ................................................................................................................................................21
Digital I/O.........................................................................................................................................................21
Temperature alarms..........................................................................................................................................22
Counter.............................................................................................................................................................22
Memory ............................................................................................................................................................22
Microcontroller.................................................................................................................................................23
USB +5V voltage .............................................................................................................................................23
Power................................................................................................................................................................23
USB specifications ...........................................................................................................................................23
Environmental ..................................................................................................................................................23
Mechanical .......................................................................................................................................................24
Screw terminal connector.................................................................................................................................24

4
Preface
About this User’s Guide
What you will learn from this user’s guide
This user's guide describes the Omega Engineering OM-USB-TC-AI data acquisition devices and lists device
specifications.
Conventions in this user’s guide
For more information about …
Text presented in a box signifies additional information and helpful hints related to the subject matter you are
reading.
Caution! Shaded caution statements present information to help you avoid injuring yourself and others,
damaging your hardware, or losing your data.
bold text Bold text is used for the names of objects on a screen, such as buttons, text boxes, and check boxes.
italic text Italic text is used for the names of manuals and help topic titles, and to emphasize a word or phrase.
Where to find more information
Additional information about OM-USB-TC-AI hardware is available on our website at www.omega.com. You
can also contact Omega Engineering by phone, fax, or email with specific questions.
Phone: [phone]
Fax: [phone]
Email: [email protected]m

5
Chapter 1
Introducing the OM-USB-TC-AI
Overview: OM-USB-TC-AI features
This user's guide contains all of the information you need to connect the OM-USB-TC-AI to your computer and
to the signals you want to measure.
The OM-USB-TC-AI is a USB 2.0 full-speed, thermocouple input module that is supported under popular
Microsoft®Windows®operating systems. The OM-USB-TC-AI is fully compatible with both USB 1.1 and
USB 2.0 ports.
The OM-USB-TC-AI provides eight analog input channels that are configured as four differential temperature
inputs and four differential or single-ended voltage inputs. A 24-bit analog-to-digital (A/D) converter is
provided for each pair of analog inputs. Eight independent, TTL-compatible digital I/O channels are provided to
monitor TTL-level inputs, communicate with external devices, and to generate alarms. The digital I/O channels
are software programmable for input or output.
The temperature channels are software programmable for different thermocouple types. You can take
measurements from type J, K, R, S, T, N, E, and B thermocouples.
The voltage input range is software programmable for ±10 V, ±5 V, ±2.5 V, ±1.25 V.
The OM-USB-TC-AI provides a integrated cold junction compensation (CJC) sensor for thermocouple
measurements. An open thermocouple detection feature lets you detect a broken thermocouple.
The OM-USB-TC-AI features eight independent temperature alarms. Each alarm controls an associated digital
I/O channel as an alarm output. The input to each alarm is one of the temperature input channels. The output of
each alarm is software configurable as active high or low. You set up the temperature threshold conditions to
activate each alarm. When an alarm is activated, the associated DIO channel is driven to the output state.
An on-board microprocessor automatically linearizes the measurement data.
The OM-USB-TC-AI is a standalone plug-and-play module which draws power from the USB cable. No
external power supply is required. All configurable options are software programmable.
The OM-USB-TC-AI is fully software calibrated.

OM-USB-TC-AI User's Guide Introducing the OM-USB-TC-AI
6
OM-USB-TC-AI block diagram
OM-USB-TC-AI functions are illustrated in the block diagram shown here.
Figure 1. OM-USB-TC-AI functional block diagram
Software features
For information on the features of InstaCal and the other software included with your OM-USB-TC-AI, refer to
the OMB-DAQ-2400, OM-USB, OM-WEB, and OM-WLS Series Data Acquisition Software User's Guide that
shipped with your device.

OM-USB-TC-AI User's Guide Introducing the OM-USB-TC-AI
7
Connecting a OM-USB-TC-AI to your computer is easy
Installing a data acquisition device has never been easier.
The OM-USB-TC-AI relies upon the Microsoft Human Interface Device (HID) class drivers. The HID
class drivers ship with every copy of Windows that is designed to work with USB ports. We use the
Microsoft HID because it is a standard, and its performance delivers full control and maximizes data
transfer rates for your OM-USB-TC-AI. No third-party device driver is required.
The OM-USB-TC-AI is plug-and-play. There are no jumpers to position, DIP switches to set, or interrupts
to configure.
You can connect the OM-USB-TC-AI before or after you install the software, and without powering down
your computer first. When you connect an HID to your system, your computer automatically detects it and
configures the necessary software. You can connect and power multiple HID peripherals to your system
using a USB hub.
You can connect your system to various devices using a standard USB cable. The USB connector replaces
the serial and parallel port connectors with one standardized plug and port combination.
You do not need a separate power supply module. The USB automatically delivers the electrical power
required by each peripheral connected to your system.
Data can flow two ways between a computer and peripheral over USB connections.

8
Chapter 2
Installing the OM-USB-TC-AI
What comes with your OM-USB-TC-AI shipment?
The following items are shipped with the OM-USB-TC-AI.
Hardware
OM-USB-TC-AI
USB cable (2 meter length)
Documentation
In addition to this hardware user's guide, you should also receive the OMB-DAQ-2400, OM-USB, OM-WEB,
and OM-WLS Series Data Acquisition Software User's Guide. This booklet supplies a brief description of the
software you received with your OM-USB-TC-AI and information regarding installation of that software.
Please read this booklet completely before installing any software or hardware.
Unpacking the OM-USB-TC-AI
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the OM-USB-TC-AI from its packaging, ground yourself using a wrist strap or by
simply touching the computer chassis or other grounded object to eliminate any stored static charge.
If any components are missing or damaged, notify Omega Engineering immediately by phone, fax, or e-mail.
Phone: [phone]
Fax: [phone]
Email: [e-mail]

OM-USB-TC-AI User's Guide Installing the OM-USB-TC-AI
9
Installing the software
Refer to the OMB-DAQ-2400, OM-USB, OM-WEB, and OM-WLS Series Data Acquisition Software User's
Guide for instructions on installing the software on the Software for OMB-DAQ-2400, OM-USB, OM-WEB, and
OM-WLS Series Data Acquisition Modules CD. This booklet is available in PDF at
www.omega.com/manuals/manualpdf/M4803.pdf.
We recommend that you download the latest Windows Update onto your computer before installing and
operating the OM-USB-TC-AI.
Installing the OM-USB-TC-AI
To connect the OM-USB-TC-AI to your system, turn your computer on, and connect the USB cable to a USB
port on your computer or to an external USB hub that is connected to your computer. The USB cable provides
power and communication to the OM-USB-TC-AI.
When you connect the OM-USB-TC-AI for the first time, a notification message opens as the OM-USB-TC-AI
is detected. When this message closes, the installation is complete. The Power LED should flash and then
remain lit. This indicates that communication is established between the OM-USB-TC-AI and your computer.
If the Power LED turns off
If the Power LED is on but then turns off, the computer has lost communication with the OM-USB-TC-AI. To
restore communication, disconnect the USB cable from the computer, and then reconnect it. This should restore
communication, and the LED should turn back on.
Configuring the OM-USB-TC-AI
All hardware configuration options on the OM-USB-TC-AI are programmable with software. Use InstaCal to
set the thermocouple type for each channel pair.
Use InstaCal to set the thermocouple type for each for each pair of temperature channels, the range and input
configuration of each voltage channel, and the alarm conditions. Any channel you don’t intend to use should be
left disabled.
Configuration options are stored on the OM-USB-TC-AI 's isolated microcontroller in EEPROM, which is non-
volatile memory on the OM-USB-TC-AI module. Configuration options are loaded on power up. The factory
default configuration is Type J thermocouple.
Default configuration
The factory default configuration for the voltage inputs is Disabled. The Disabled mode disconnects the analog
inputs from the terminal blocks and internally grounds all of the A/D inputs.
Warm up
Allow the OM-USB-TC-AI to warm up for 30 minutes after powering up before taking measurements. This
warm up time minimizes thermal drift and achieves the specified rated accuracy of measurements.
Calibrating the OM-USB-TC-AI
The OM-USB-TC-AI is fully calibrated via InstaCal. Allow the OM-USB-TC-AI to operate for at least 30
minutes before calibrating. This warm up time minimizes thermal drift and achieves the specified rated
accuracy of measurements.

10
Chapter 3
Signal I/O Connections
Screw terminal pinout
The OM-USB-TC-AI has four rows of screw terminals —two rows on the top edge of the housing, and two
rows on the bottom edge. Each row has 26 connections. Between screw terminals 10 and 11 is the integrated
CJC sensor used for thermocouple measurements. Signals are identified in Figure 2.
Figure 2. OM-USB-TC-AI screw terminal pin numbers

OM-USB-TC-AI User's Guide Signal I/O Connections
11
OM-USB-TC-AI screw terminal descriptions
Pin
Signal Name
Pin Description
Pin
Signal Name
Pin Description
1
RSVD
Reserved, Do Not Use
27
GND
2
NC
28
V3L
V3 voltage input (-)
3
T0H
T0 sensor input (+)
29
V3H
V3 voltage input (+)
4
T0L
T0 sensor input (-)
30
GND
5
4W01
T0/T1 4-wire, 2 sensor common
31
V2L
V2 voltage input (-)
6
RSVD
Reserved, Do Not Use
32
V2H
V2 voltage input (+)
7
T1H
T1 sensor input (+)
33
GND
8
T1L
T1 sensor input (-)
34
V1L
V1 voltage input (-)
9
GND
35
V1H
V1 voltage input (+)
10
RSVD
Reserved, Do Not Use
36
GND
CJC sensor
11
RSVD
Reserved, Do Not Use
37
V0L
V0 voltage input (-)
12
NC
38
V0H
V0 voltage input (+)
13
T2H
T2 sensor input (+)
39
GND
14
T2L
T2 sensor input (-)
40
CTR
Counter Input
15
4W23
T2/T3 4-wire, 2 sensor common
41
DIO7
Digital Input/Output
16
RSVD
Reserved, Do Not Use
42
DIO6
Digital Input/Output
17
T3H
T3 sensor input (+)
43
DIO5
Digital Input/Output
18
T3L
T3 sensor input (-)
44
DIO4
Digital Input/Output
19
GND
45
DIO3
Digital Input/Output
20
RSVD
Reserved, Do Not Use
46
DIO2
Digital Input/Output
21
+5V
+5V output
47
DIO1
Digital Input/Output
22
GND
48
DIO0
Digital Input/Output
23
NC
49
GND
24
NC
50
NC
25
NC
51
NC
26
NC
52
NC
Use 16 AWG to 30 AWG wire for your signal connections.
Tighten screw terminal connections
When making connections to the screw terminals, be sure to tighten the screw until tight. Simply touching the
top of the screw terminal is not sufficient to make a proper connection.
Voltage input terminals (±V0H/V0L to ±V3H/V3L)
You can connect up to four voltage inputs to the voltage channels (V0H/V0L to V3H/V3L). The input range is
software programmable for ±10 V, ±5 V, ±2.5 V, or ±1.25 V. Each voltage channel is software configurable for
differential or single-ended mode.
When connecting differential inputs to floating input sources, you must provide a DC return path from each
differential input to ground. One way to do this is to connect a resistor from one side of each of the differential
inputs to GND. A value of approximately 100 kΩ can be used for most applications.
Caution! All ground pins on the OM-USB-TC-AI (pins 9, 19, 22, 27, 30, 33, 36, 39, 49) are common and
are isolated from earth ground. If a connection is made to earth ground when using digital I/O and
conductive thermocouples, the thermocouples are no longer isolated. In this case, thermocouples
must not be connected to any conductive surfaces that may be referenced to earth ground.
Thermocouple input terminals (T0H/T0L to T3H/T3L)
You can connect up to four thermocouples to the differential sensor inputs (T0H/T0L to T3H/T3L). The OM-
USB-TC-AI supports type J, K, R, S, T, N, E, and B thermocouples. You can mix thermocouple types (J, K, R,
S, T, N, E, and B).

OM-USB-TC-AI User's Guide Signal I/O Connections
12
Thermocouple selection
The thermocouple type you select will depend on your application needs. Review the temperature ranges and
accuracies of each type to determine which is best suited for your application.
Ground terminals (GND)
The six analog ground terminals (GND) provide a common ground for the input channels and DIO bits and are
isolated (500 VDC) from the USB GND.
Power terminals (+5V)
The two +5V terminals are isolated (500 VDC) from the USB +5V.
Digital terminals (DIO0 to DIO7)
You can connect up to eight digital I/O lines to the screw terminals labeled DIO0 to DIO7. Each terminal is
software configurable for input or output.
If a digital bit is set up as an alarm, the bit is configured for output on power-up, and assumes the state defined
by the alarm configuration
Counter terminal (CTR)
The CTR terminal (pin 40) is the input to the 32-bit event counter. The internal counter increments when the
TTL level transitions from low to high. The counter can count events at frequencies of up to 1 MHz.
Caution! All ground pins on the OM-USB-TC-AI (pins 9, 19, 22, 27, 30, 33, 36, 39, 49) are common and
are isolated from earth ground. If a connection is made to earth ground when using digital I/O and
conductive thermocouples, the thermocouples are no longer isolated. In this case, thermocouples
must not be connected to any conductive surfaces that may be referenced to earth ground.
CJC sensor
The OM-USB-TC-AI has one built-in high-resolution temperature sensor. The CJC sensor measures the
ambient temperature at the terminal block so that the cold junction voltage can be calculated.
Thermocouple connections
A thermocouple consists of two dissimilar metals that are joined together at one end. When the junction of the
metals is heated or cooled, a voltage is produced that correlates to temperature.
The OM-USB-TC-AI makes fully differential thermocouple measurements without the need of ground-
referencing resistors. A 32-bit floating point value in either a voltage or temperature format is returned by
software. An open thermocouple detection feature is available for each thermocouple input which automatically
detects an open or broken thermocouple.
Use InstaCal to select the thermocouple type (J, K, R, S, T, N, E, and B) on one or more sensor input channels
to connect the thermocouple.
Wiring configuration
Connect the thermocouple to the OM-USB-TC-AI using a differential configuration, as shown in Figure 3.

OM-USB-TC-AI User's Guide Signal I/O Connections
13
Figure 3. Typical thermocouple connection
Connect thermocouples to the OM-USB-TC-AI such that they are floating with respect to GND (pins 9, 19, 28,
38). The OM-USB-TC-AI GND pins are isolated from earth ground, so connecting thermocouple sensors to
voltages referenced to earth ground is permissible as long as the isolation between the GND pins (9, 19, 28, 38)
and earth ground is maintained.
When thermocouples are attached to conductive surfaces, the voltage differential between multiple
thermocouples must remain within ±1.4 V. For best results, we recommend the use of insulated or ungrounded
thermocouples when possible.
Maximum input voltage between analog input and ground
The absolute maximum input voltage between an analog input and the isolated GND pins is ±25 VDC when the
OM-USB-TC-AI is powered on, and ±40 VDC when the OM-USB-TC-AI is powered off.
If you need to increase the length of your thermocouple, use the same type of thermocouple wires to minimize
the error introduced by thermal EMFs.
Digital I/O connections
You can connect up to eight digital I/O lines to the screw terminals labeled DIO0 to DIO7. You can configure
each digital bit for either input or output. All digital I/O lines are pulled up to +5V with a 47 kΩ resistor
(default). You can request the factory to configure the resistor for pull-down to ground if desired.
Caution! If a digital bit is set up as an alarm, the bit will be configured for output on power-up, and assume
the state defined by the alarm configuration.
When you configure the digital bits for input, you can use the OM-USB-TC-AI digital I/O terminals to detect
the state of a TTL-compatible device. Refer to the schematic shown in Figure 4. If you set the switch to the +5V
input, DIO0 reads TRUE (1). If you move the switch to GND, DIO0 reads FALSE (0).
Figure 4. Schematic showing switch detection by digital channel DIO0
All ground pins on the OM-USB-TC-AI (pins 9, 19, 22, 27, 30, 33, 36, 39, 49) are isolated from earth ground. If
a connection is made to earth ground when using digital I/O and conductive thermocouples, the thermocouples
are no longer isolated. In this case, thermocouples must not be connected to any conductive surfaces that may
be referenced to earth ground
For general information regarding digital signal connections and digital I/O techniques, refer to the OMB-DAQ-
2416 Series and OM-USB Series General Guide to Signal Connections (available on our web site at
www.omega.com/manuals/manualpdf/M4830.pdf).

OM-USB-TC-AI User's Guide Signal I/O Connections
14
Configuring the DIO channels to generate alarms
The OM-USB-TC-AI features eight independent temperature alarms. All alarm options are software
configurable.
When a digital bit is configured as an alarm, that bit is configured as an output on the next power cycle and
assumes the state defined by the alarm configuration.
Each alarm controls an associated digital I/O channel as an alarm output. The input to each alarm is one of the
temperature input channels. You set up the temperature conditions to activate an alarm, and the output state of
the channel (active high or low) when activated. When an alarm is activated, its associated DIO channel is
driven to the output state specified.
The alarm configurations are stored in non-volatile memory and are loaded on power up. The temperature
alarms function both in data logging mode and while attached to the USB port on a computer.

15
Chapter 4
Functional Details
Thermocouple measurements
A thermocouple consists of two dissimilar metals that are joined together at one end. When the junction of the
metals is heated or cooled, a voltage is produced that correlates to temperature.
The OM-USB-TC-AI hardware level-shifts the thermocouple’s output voltage into the A/D’s common mode
input range by applying +2.5 V to the thermocouple’s low side at the C#L input. Always connect thermocouple
sensors to the OM-USB-TC-AI in a floating fashion. Do not attempt to connect the thermocouple low side C#L
to GND or to a ground referencing resistor.
Cold junction compensation (CJC)
When you connect the thermocouple sensor leads to the sensor input channel, the dissimilar metals at the OM-
USB-TC-AI terminal blocks produce two additional thermocouple junctions. This junction creates a small
voltage error term which must be removed from the overall sensor measurement using a cold junction
compensation technique. The measured voltage includes both the thermocouple voltage and the cold junction
voltage. To compensate for the additional cold junction voltage, the OM-USB-TC-AI subtracts the cold junction
voltage from the thermocouple voltage.
The OM-USB-TC-AI has one high-resolution temperature sensor integrated into the design. The CJC sensor
measures the average temperature at the terminal block so that the cold junction voltage can be calculated. A
software algorithm automatically corrects for the additional thermocouples created at the terminal blocks by
subtracting the calculated cold junction voltage from the analog input's thermocouple voltage measurement.
Increasing the thermocouple length
If you need to increase the length of your thermocouple, use the same type of thermocouple wires to minimize
the error introduced by thermal EMFs.
Data linearization
After the CJC correction is performed on the measurement data, an on-board microcontroller automatically
linearizes the thermocouple measurement data using National Institute of Standards and Technology (NIST)
linearization coefficients for the selected thermocouple type.
The measurement data is then output as a 32-bit floating point value in the configured format (voltage or
temperature).
Open-thermocouple detection (OTD)
The OM-USB-TC-AI is equipped with open-thermocouple detection for each analog input channel. With OTD,
any open-circuit or short-circuit condition at the thermocouple sensor is detected by the software. An open
channel is detected by driving the input voltage to a negative value outside the range of any thermocouple
output. The software recognizes this as an invalid reading and flags the appropriate channel. The software
continues to sample all channels when OTD is detected.
USB connector
The USB connector provides +5V power and communication. No external power supply is required.
LEDs
OM-USB-TC-AI has two LEDs –Power and Activity.
The Power LED (top) turns on when the device is detected and installed on the computer.
The Activity LED (bottom) blinks when data is transferred, and is off otherwise.

OM-USB-TC-AI User's Guide Functional Details
16
Power
The two +5V terminals are isolated (500 VDC) from the USB +5V.
Caution! Each +5V terminal is an output. Do not connect to an external power supply or you may damage
the OM-USB-TC-AI and possibly the computer.

17
Chapter 5
Specifications
Typical for 25 °C unless otherwise specified.
All specifications apply to all temperature and voltage input channels unless otherwise specified.
Specifications in italic text are guaranteed by design.
Analog input
Table 1. Generic analog input specifications
Parameter
Conditions
Specification
A/D converter type
T0x-T3x, V0x-V3x
AD42_321
Dual 24-bit Sigma-Delta
Number of channels
Voltage input V0x-V3x
4 differential, 4 single-ended
Temperature input T0x-T3x
4 differential
Input isolation
500 VDC minimum between field wiring and USB
interface
Channel configuration
T0x-T3x
Temperature input.
Software programmable to match sensor type
V0x-V3x
Voltage input
Analog input modes
Power up and reset state
Factory default configuration is Disabled mode.
Once configured, each channel reverts to the mode
previously set by the user.
Single-ended
Vx_H inputs are connected directly to their screw
terminal pins.
Vx_L inputs are disconnected from their screw
terminal pins and internally connected to GND.
Differential
Vx_H and Vx_L inputs are connected directly to
their screw terminal pins.
Tx_H and Tx_L inputs are connected directly to their
screw terminal pins.
Input ranges
Thermocouple
T0x-T3x
±0.080 V
Voltage
V0x to V3x
±10 V, ±5 V, ±2.5 V, ±1.25 V
software selectable
Absolute max input voltage
T0x to T3x relative to GND
±25 V max (power on)
±40 V max (power off)
V0x to V3x relative to GND
±25 V max (power on)
±15 V max (power off)
Input impedance
T0x to T3x
5 GΩ (power on)
1MΩ (power off)
V0x to V3x
10 GΩ (power on)
2.49 kΩ (power off)
Input leakage current
T0x to T3x, with open
thermocouple detect disabled.
30 nA max
T0x-T3x, with open
thermocouple detect enabled.
105 nA max
V0x to V3x
±1.5 nA typ, ±25 nA max
Input bandwidth
(–3 dB)
T0x to T3x
50 Hz
V0x to V3x
3 kHz
Maximum working voltage
(signal + common mode)
V0x to V3x
±10.25 V max

OM-USB-TC-AI User's Guide Specifications
18
Parameter
Conditions
Specification
Common mode rejection ratio
T0x to T3x, fIN = 60 Hz
100 dB
V0x to V3x, fIN = 60 Hz, all
input ranges
83 dB
ADC resolution
24 bits
ADC No missing codes
24 bits
Input coupling
DC
Warm-up time
30 minutes min
Open thermocouple detect
T0x to T3x
Automatically enabled when the channel pair is
configured for thermocouple sensor.
The max open detection time is 3 seconds.
CJC sensor accuracy
T0x to T3x, 15 °C to 35 °C
±0.25 °C typ,±0.5 °C max
T0x to T3x, 0°C to 70 °C
–1.0 to +0.75 °C max
Channel configurations
Table 2. Channel configuration specifications
Channel
Category
Conditions
Specification
T0x to T3x
Disabled
All temperature input channels are disconnected from screw
terminals and internally connected to GND.
See Note 4
T0x to T3x
Thermocouple
Note 1
4 differential channels
V0x to V3x
Disabled
All voltage input channels are disconnected from screw
terminals and internally connected to GND.
See Note 4
V0x to V3x
Differential
Note 2
4 differential channels
V0x to V3x
Single-ended
4 single-ended
channels
Note 1: Internally, the OM-USB-TC-AI has four, dual-channel, fully differential A/Ds providing a total of
eight input channels.
Note 2: When connecting differential inputs to floating input sources, you must provide a DC return path from
each differential input to ground. To do this, connect a resistor from each of the differential inputs to
GND. A value of approximately 1Meg ohm can be used for most applications.
Note 3: Channel configuration information is stored in the EEPROM of the isolated microcontroller by the
firmware whenever any item is modified. Modification is performed by commands issued over USB
from an external application, and the configuration is made non-volatile through the use of the
EEPROM.
Note 4: The factory default configuration is Disabled. The Disabled mode will disconnect the temperature and
voltage inputs from the terminal blocks and internally connect ground (GND) to all of the A/D inputs.
Compatible sensors: T0x toT3x
Table 3. Compatible sensor type specifications
Parameter
Conditions (°C)
Thermocouple
J: –210 to 1200
K: –270 to 1372
R: –50 to 1768
S: –50 to 1768
T: –270 to 400
N: –270 to 1300
E: –270 to 1000
B: 0 to 1820

OM-USB-TC-AI User's Guide Specifications
19
Accuracy
Thermocouple measurement accuracy: T0x to T3x
Table 4. Thermocouple accuracy specifications, including CJC measurement error. All specifications are (±)
Sensor
Type
Sensor temperature
range (°C)
Accuracy error
maximum (°C)
Accuracy error
Typical (°C)
Tempco
(°C/°C)
J
–210
2.028
0.707
0.031
0
0.835
0.278
1200
0.783
0.288
K
–210
2.137
0.762
0.035
0
0.842
0.280
1372
0.931
0.389
S
–50
1.225
0.435
0.021
250
0.554
0.195
1768
0.480
0.157
R
–50
1.301
0.458
0.019
250
0.549
0.190
1768
0.400
0.134
B
250
2.193
2.185
0.001
700
0.822
0.819
1820
0.469
0.468
E
–200
1.976
0.684
0.030
0
0.954
0.321
1000
0.653
0.240
T
–200
2.082
0.744
0.035
0
0.870
0.290
400
0.568
0.208
N
–200
2.197
0.760
0.028
0
0.848
0.283
1300
0.653
0.245
Note 5: Thermocouple measurement accuracy specifications include polynomial linearization, cold-junction
compensation and system noise. These specs are for one year, or 3000 operating hours, whichever
comes first, and for operation of the OM-USB-TC-AI between 15 °C and 35 °C. There is a CJC sensor
on the temperature sensor input side of the module. The accuracy listed above assumes the screw
terminals are at the same temperature as the CJC sensor. Errors shown do not include inherent
thermocouple error. Contact your thermocouple supplier for details on the actual thermocouple
accuracy error.
Note 6: Thermocouples must be connected to the OM-USB-TC-AI such that they are floating with respect to
GND. The OM-USB-TC-AI GND pins are isolated from earth ground. You can connect thermocouple
sensors to voltages referenced to earth ground as long as the isolation between the GND pins and earth
ground is maintained.
Note 7: When thermocouples are attached to conductive surfaces, the voltage differential between multiple
thermocouples must remain within ±1.4 V. For best results, we recommend using insulated or
ungrounded thermocouples when possible.