Thermocouple Measurement Applications
Data Acquisition Processor boards are excellent for multi-channel, long-term acquisition of thermocouple measurements. Thermocouples have several advantages.
- convenient and inexpensive
- rugged, able to withstand brutal temperature extremes
- with calibration, accurate and repeatable within a fraction of a degree
- well-known characteristics dependent on fundamental material properties
But thermocouples also have two major drawbacks. Data Acquisition Processors are ideally suited for dealing with these difficulties.
- Measurements depend on small changes in the contact potential between dissimilar materials. The readings require a high-impedance detector and are very noisy.
Fortunately, their response is also very slow. There is plenty of time to collect hundreds or thousands of differential samples, and average them to produce relatively quiet measurements. There is no need to clog your front-end application with this bulk processing when all your application needs is temperature results. The Data Acquisition Processor is easily configured to perform all pre-processing. - Thermocouples have a non-linear response that depends both on the measured and ambient temperature.
For applications where standard conversion curves are sufficiently accurate (typically +/- 2 degrees C), theTHERMOcommand provided by the DAPL system knows all of the common thermocouple types and applies conversions to temperature units automatically. You can specify the ambient temperature or sense it independently for automatic cold junction compensation.
Typical Equipment
Processor |
DAP 840 resident in the host processor case. |
Connections |
MSTB 010 termination board. |
Cable |
Cable MSCBL 048 or MSCBL 050. |
Example
- 8 type-J thermocouples measuring a high temperature chemical reactor process
- sample each sensor 500 times per second and average to reduce noise
- fixed ambient temperatures 22 degrees C in controlled environment
- convert from raw D/A converter range of 0 to 32767 into scaled range 0 to 50000 microvolts
- temperature measurements reported once per second on each channel
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