Measurement Computing WEB-TEMP - Manual (Page 16)

WEB-TEMP User's Guide Signal Connections
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Do not connect two different sensor categories to the same channel pair
The WEB-TEMP provides a 24-bit A/D converter for each channel pair. Each channel pair can monitor one
sensor category. To monitor a sensor from a different category, connect the sensor to a different channel pair.
Current excitation outputs
The WEB-TEMP has four dedicated pairs of current excitation output terminals (± IA to ± ID ). These terminals
have a built-in precision current source to provide excitation for the resistive sensors used for RTD and
thermistor measurements.
Each current excitation terminal is dedicated to one pair of sensor input channels:
 IA+ is the current excitation source for channel 0 and channel 1
 IB+ is the current excitation source for channel 2 and channel 3
 IC+ is the current excitation source for channel 4 and channel 5
 ID+ is the current excitation source for channel 6 and channel 7
Four-wire, two sensor common
Terminals 4W01 , 4W23 , 4W45 , and 4W67 are the common connection for four-wire configurations with two
RTD or thermistor sensors.
Four-wire, two sensor common
Terminals IC01 , IC23 , IC45 , and IC67 are used as the common connection for four-wire configurations with two
RTD or thermistor sensors.
CJC sensors
The WEB-TEMP has four built in high-resolution temperature sensors for thermocouple measurements. Each
CJC sensor is dedicated to one of the four channel pairs, and is located behind the associated channel's screw
terminal. These sensors measure 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. A PU/D terminal is provided for pull-up/down configuration.
If a digital bit is set up as an alarm, the bit is configured for output and assumes the state defined by the alarm
configuration.
Pull-up/down configuration
All digital I/O lines are connected through 47 kΩ 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.
Analog and digital ground
The analog ground ( AGND ) terminals provide a common ground for the sensor input channels. 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 ground ( GND ) terminal provides a common ground for the digital I/O channels. The GND pin is isolated
from the AGND pins and from earth ground.
Power output
The +5V output terminal is isolated (500 VDC) from the analog input terminals.
Caution! The +5V terminal is an output. Do not connect an external power supply to this terminal or you
may damage the WEB-TEMP and possibly the computer.