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OMB-DAQ-2416-4AO User's Guide Functional Details
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The OMB-DAQ-2416-4AO also provides an open thermocouple detection (OTD) feature for each of the analog
input channels configured for thermocouple measurement. This feature is automatically enabled as part of the
overall acquisition process, and detects if an open-circuit condition exists at the thermocouple sensor.
The OMB-DAQ-2416-4AO provides electrostatic discharge (ESD) protection for each of the thermocouple
inputs. However, before handling thermocouple sensors, follow standard ESD practices and discharge any
accumulated ESD charge.
The OMB-DAQ-2416-4AO includes an ESD protection device at each of the analog input terminal block pins.
If an ESD or transient voltage is coupled into the device, the input protection device(s) clamps the voltage to
protect the thermocouple input circuitry from possible damage.
Once the thermocouple sensor is connected to the OMB-DAQ-2416-4AO, the configuration options have been
selected, and the recommended 45 minute warm up has elapsed, the OMB-DAQ-2416-4AO is ready to make
high-resolution differential voltage measurements.
Cold junction compensation (CJC) is needed to compensate for the additional thermal EMF's generated by
connecting the thermocouple leads to the OMB-DAQ-2416-4AO terminal blocks.
CJC is performed using a high-resolution temperature sensor connected close to the OMB-DAQ-2416-4AO's
terminal blocks. The OMB-DAQ-2416-4AO includes four separate CJC sensors—two on each side of the PCB.
Software corrects for the additional thermocouples created at the terminal.
Once the A/D and CJC data is collected, the application software uses this data to linearize to an accurate
temperature reading. The thermocouple linearization uses the latest NIST linearization coefficients for each of
the eight thermocouple types supported by the OMB-DAQ-2416-4AO.
Figure 11 below shows a typical thermocouple connection.
Figure 11. Differential thermocouple connection example
Noise filtering, data rate, and throughput rate
Although the OMB-DAQ-2416-4AO's A/D converter has a maximum data rate of 3,750 samples per second,
the actual throughput rate you observe for voltage and temperature data is determined by these formulas.
Maximum single-channel throughput:
s
ratedata
640
1
1