USB-TC-AI User's Guide
Signal I/O Connections
11
Thermocouple input
You can connect up to four thermocouples to the differential sensor inputs (
T0H
/
T0L
to
T3H
/
T3L
). The device
supports type J, K, R, S, T, N, E, and B thermocouples. You can mix thermocouple types.
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.
CJC sensor
The 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.
Digital I/O
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.
Counter input
The
CTR
terminal 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 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.
Power output
The two
+5V output
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 USB-TC-AI and possibly the computer.
Ground
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.
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 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
Insta
Cal 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 USB-TC-AI using a differential configuration, as shown in Figure 3.
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