OM-WEB Series User's Guide
Specifications
32
Channel configurations
Table 2. Channel configuration specifications
Sensor Category
Condition
Max number of
sensors (all channels
configured alike)
Disabled
All temperature input channels are disconnected from screw
terminals and internally connected to AGND.
See Note 2
Thermocouple (Note 1)
8 differential channels
Semiconductor (Note 1)
OM-WEB-TEMP only
8 differential channels
RTD and Thermistor
(Note 1)
OM-WEB-TEMP only
2-wire input configuration with a single sensor per channel pair
4 differential channels
2-wire input configuration with two sensors per channel pair
8 differential channels
3-wire configuration with a single sensor per channel pair
4 differential channels
4-wire input configuration with a single sensor per channel pair
4 differential channels
4-wire input configuration with two sensors per channel pair
8 differential channels
Note 1:
Internally, OM-WEB Series devices have four, dual-channel, fully differential A/Ds providing a total
of eight differential channels. The analog input channels are configured in four channel pairs, with
CH0/CH1 sensor inputs, CH2/CH3 sensor inputs, CH4/CH5 sensor inputs, and CH6/CH7 sensor
inputs paired together. This "channel-pairing" requires the analog input channel pairs be configured to
monitor the same category of temperature sensor. Mixing different sensor types of the same category
(such as a type J thermocouple on channel 0 and a type T thermocouple on channel 1) is permissible.
The factory default thermocouple configuration is
Type J
.
Channel configuration information is stored on a EEPROM external to the isolated microcontroller by
the firmware whenever any item is modified. Modification is performed by commands issued over
Ethernet from an external application, and the configuration is made non-volatile through the use of the
EEPROM.
Note 2:
The factory default sensor configuration is
Disabled
. The Disabled mode disconnects the analog inputs
from the terminal blocks, and internally grounds (AGND) all of the A/D inputs. This mode also
disables each of the current excitation sources.
Compatible sensors
Table 3. Compatible sensor type specifications
Parameter
Condition
Thermocouple
J: –210 °C to 1200 °C
K: –270 °C to 1372 °C
R: –50 °C to 1768 °C
S: –50 °C to 1768 °C
T: –270 °C to 400 °C
N: –270 °C to 1300 °C
E: –270 °C to 1000 °C
B: 0 °C to 1820 °C
RTD
(OM-WEB-TEMP only)
100 Ω PT (DIN 43760: 0.00385 ohms/ohm/°C)
100 Ω PT (SAMA: 0.003911 ohms/ohm/°C)
100 Ω PT (ITS-90/IEC751:0.0038505 ohms/ohm/°C)
Thermistor
(OM-WEB-TEMP only)
Standard 2,252 Ω through 30,000 Ω
Semiconductor / IC
(OM-WEB-TEMP only)
LM35, TMP35 or equivalent
