OMB-DAQ-2408 Series User's Guide
Functional Details
15
For more information on analog signal connections
For more information on single-ended and differential inputs, refer to the
OMB-DAQ-2400, OM-USB,
OM-WEB, and OM-WLS Series General Guide to Signal Connections
(available on our web site at
www.omega.com/manuals/manualpdf/M4830.pdf
).
TC input mode
You can make up to eight high-resolution DIFF TC measurements with a OMB-DAQ-2408 Series device.
Built-in cold-junction compensation sensors are provided for each of the screw-terminal blocks and any
supported TC type can be attached to any of the 8 TC channels.
Do not connect TCs as
SE
– doing so can cause false readings.
You do not need to use ground-referencing resistors for TC inputs because the analog front-end circuit level-
shifts the TC output into the common-mode input range of the A/D.
OMB-DAQ-2408 Series devices also provide an open TC detection feature for each of the analog input
channels configured for TC measurement. This feature is enabled or disabled by software, and when enabled, it
detects if an open-circuit condition exists at the TC sensor.
OMB-DAQ-2408 Series devices provide electrostatic discharge (ESD) protection for each of the TC inputs.
However, before handling TC sensors, follow standard ESD practices and discharge any accumulated ESD
charge
.
Once the TC sensor is connected to the device, the configuration options have been selected, and the
recommended 45 minute warm up has elapsed, the device is ready to make high-resolution DIFF temperature
measurements.
Built-in cold junction compensation (CJC) automatically compensates for the additional thermal EMFs
generated by connecting the TC leads to the OMB-DAQ-2408 Series device terminal blocks.
CJC is performed using a high-resolution temperature sensor connected close to the device terminal blocks. The
device includes two separate CJC sensors – one on each side of the PCB. Software corrects for the additional
TCs created at the terminals.
Once the A/D and CJC data is collected, the application software uses this data to linearize to an accurate
temperature reading. The TC linearization uses the latest NIST linearization coefficients for each of the eight
TC types supported by OMB-DAQ-2408 Series devices.
When configuring TC sensors, keep any stray capacitance as small as possible relative to AGND to avoid
settling time and accuracy errors. For TC channels, do not provide a return path to ground. This is done
internally.
Figure 7 shows a typical TC connection.
Figure 7. DIFF TC connection example
