OM-USB-TEMP-AI User's Guide
Specifications
25
Note 5:
Thermocouple measurement accuracy specifications include polynomial linearization,
cold-junction compensation and system noise. These specs are for one year, or 3000 operating
hours, whichever comes first, and for operation of the OM-USB-TEMP-AI between 15 °C and
35 °C. There is a CJC sensor on each temperature sensor input side of the module. The accuracy
listed above assumes the screw terminals are at the same temperature as the CJC sensor. Errors
shown do not include inherent thermocouple error. Contact your thermocouple supplier for
details on the actual thermocouple accuracy error.
Note 6:
Thermocouples must be connected to the OM-USB-TEMP-AI such that they are floating with
respect to GND (pins 9, 19, 22, 27, 30, 33, 36, 39, 49). The OM-USB-TEMP-AI GND pins are
isolated from earth ground. You can connect thermocouple sensors to voltages referenced to earth
ground as long as the isolation between the GND pins and earth ground is maintained.
Note 7:
When thermocouples are attached to conductive surfaces, the voltage differential between
multiple thermocouples must remain within ±1.4 V. For best results, we recommend using
insulated or ungrounded thermocouples when possible.
Semiconductor sensor measurement accuracy: T0x-T3x
Table 5. Semiconductor sensor accuracy specifications
Sensor type
Temperature Range
Accuracy Error maximum
TMP36 or equivalent
-40 to 150 °C
±0.50 °C
Note 8:
Error shown does not include errors of the sensor itself. These specifications are for one year
while operation of the OM-USB-TEMP-AI unit is between 15 °C and 35 °C. Contact your sensor
supplier for details on the actual sensor error limitations.
RTD measurement accuracy: T0x-T3x
Table 6. RTD measurement accuracy specifications, Ix+ = 210 µA. All specifications are (±).
RTD
Sensor temperature
range
Accuracy error (°C)
maximum
Accuracy error (°C)
typical
Tempco
(°C/°C)
-200 °C
2.913
2.784
0.001
-150 °C
1.201
1.070
0.001
-100 °C
0.482
0.349
0.001
0 °C
0.261
0.124
0.001
100 °C
0.269
0.127
0.001
300 °C
0.287
0.136
0.001
PT100, DIN,
US or ITS-90
600 °C
0.318
0.150
0.001
Note 9:
The error shown does not include errors of the sensor itself. The sensor linearization is performed
using a Callendar-Van Dusen linearization algorithm. The accuracy and tempco specifications
include
the accuracy of the Callendar-Van Dusen linearization algorithm. These specifications
are for one year while operation of the OM-USB-TEMP-AI unit is between 15 °C and 35 °C. The
specification does not include lead resistance errors for 2-wire RTD connections. Please contact
your sensor supplier for details on the actual sensor error limitations.
Note 10:
Resistance values greater than 660 ohms cannot be measured by the OM-USB-TEMP-AI in the
RTD mode. The 660 ohm resistance limit includes the total resistance across the current
excitation (±Ix) pins, which is the sum of the RTD resistance and the lead resistances.
Note 11:
For accurate three wire compensation, the individual lead resistances connected to the ±Ix pins
must be of equal ohmic value. To ensure this, use connection leads of equal lengths.
