WLS-TC User's Guide
Sensor Connections
13
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.
Power outputs
The two
+5V
output terminals are isolated (500 VDC) from the USB +5V.
Ground
The six 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 WLS-TC 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 which automatically detects an open or broken thermocouple is available
for each analog input.
Use InstaCal to select the thermocouple type (J, K, R, S, T, N, E, and B) and one or more sensor input channels
to connect the thermocouple.
Wiring configuration
Connect the thermocouple to the WLS-TC using a differential configuration, as shown in Figure 3.
Figure 3. Typical thermocouple connection
Connect thermocouples to the WLS-TC so that they float with respect to GND (pins 9, 19, 28, 38). The WLS-
TC
GND
pins are isolated from earth ground, so you can connect thermocouple sensors to voltages referenced to
earth ground as long as you maintain the isolation between the GND pins (9, 19, 28, 38) and earth ground.
When you attach thermocouples to conductive surfaces, the voltage differential between multiple
thermocouples must remain within ±1.4 V. For best results, use 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
WLS-TC is powered on, and ±40 VDC when the WLS-TC 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.
