OM-WEB Series User's Guide
Signal I/O Connections
18
Current excitation output (OM-WEB-TEMP)
Four dedicated pairs of current excitation output terminals (±
IA
to ±
ID
) have a built-in precision current source
to provide excitation for the resistive sensors used for RTD and thermistor measurements.
Current excitation terminals are dedicated to one pair of sensor input channels:
IA+ and IA– are the current excitation source for channel 0 and channel 1
IB+ and IB– are the current excitation source for channel 2 and channel 3
IC+ and IC– are the current excitation source for channel 4 and channel 5
ID+ and ID– are the current excitation source for channel 6 and channel 7
These terminals are labeled RSVD (reserved for future use) on the OM-WEB-TC.
Four-wire, two sensor common (OM-WEB-TEMP)
Terminals
4W01
,
4W23
,
4W45
, and
4W67
are used as the common connection for four-wire configurations with
two RTD or thermistor sensors.
These terminals are labeled RSVD (reserved for future use) on the OM-WEB-TC.
Four-wire, two sensor common (OM-WEB-TEMP)
Terminals
IC01
,
IC23
,
IC45
, and
IC67
are used as the common connection for four-wire configurations with two
RTD or thermistor sensors.
These terminals are labeled RSVD (reserved for future use) on the OM-WEB-TC.
CJC sensors
OM-WEB Series hardware have 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
(explained below).
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
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
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 OM-WEB-TEMP, OM-WEB-TC and possibly the computer.
