Measurement-computing WEB-TC Manuel d'utilisateur télécharger pdf (Page 19)

WEB-TC User's Guide Signal I/O Connections

Pull-up/down terminal (PU/D)

All digital I/O lines are connected through 47k to the PU/D pin, which is floating by default. For a pull-up

configuration, connect the PU/D pin to the +5V pin. For a pull-down configuration, connect the PU/D pin to the

GND pin.

Ground terminals (AGND and GND)

The analog ground (AGND) terminals (pins 9, 19, 28, 38) provide a common ground for the thermocouple input

channels. The AGND pins are isolated from the GND pin and from earth ground. Thermocouple sensors can

connect to voltages that are referenced to earth ground, as long the isolation between the AGND pins and earth

ground is maintained.

The digital ground (GND) terminal (pin 48) provides a common ground for the digital I/O channels. The GND

pin is isolated from the AGND pins and from earth ground.

Power terminal (+5V)

The +5V output terminal is isolated (500 VDC) from the thermocouple input channels.

Caution! The +5V terminal is an output. Do not connect an external power supply to this terminal or you

may damage the WEB-TC and possibly the computer.

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 WEB-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 is available for each analog input which automatically detects an open or

broken thermocouple.

Use the web interface or InstaCal to select the thermocouple type (J, K, R, S, T, N, E, and B) and one or more

sensor input channel to connect the thermocouple.

Wiring configuration

Connect the thermocouple to the WEB-TC using a differential configuration, as shown in Figure 3.

Figure 3. Typical thermocouple connection

Note: There are two high/low channel pairs on each terminal. The # indicates the channel number. Do not

connect any signal or sensor to the pins labeled "NC" or "RSVD". These pins must remain disconnected for the

WEB-TC to operate according to specification.

Thermocouples must be connected to the WEB-TC such that they are floating with respect to AGND (pins 9,

19, 28, and 38). The WEB-TC AGND 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 AGND pins and earth

ground is maintained.

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Measurement-computing WEB-TC Manuel d'utilisateur Page 19