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2.10 Using OME-DB-8225 CJC Output
The OME-DB-8225 daughter board contains built-in cold junction
compensation (CJC) circuitry that provides a 10mV per Deg C output. With 0.0
Volts @ -273 Deg C. The OME-A-822 should be protected from drafts and
direct sunlight in order to accurately reflect room temperature.
CJC Calibration:
1. Connect the OME-A-822PGL/PGH to the OME-DB-8225 CN1
2. Set the OME-A-822PGL/PGH to single-ended Mode
3. Set the JP1 jumper to 1-2 and the JP2 jumper to 2-3 ( single-ended mode)
4.Read the temperature from a digital thermometer placed near D1/D2(See the
OME-DB-8225 Layout) .
5.Read OME-A-822PGL/PGH analog input channel 0 (single-ended Channel 0)
6.Adjust VR1 until a stable reading of 10mV per deg C is attained .
For example, when the ambient temperature is 24 deg C. the reading value
of CJC will be 2.97V
(273 deg c +24 deg c ) X 10 mV/deg c = 2.97V
You will need an A/D channel for the CJC calibration. AI0 is reserved for CJC
calibration when used in single-ended mode and CH0-HI & CH0-LO is reserved for the
differential mode. differential mode is recommended when working with thermocouples.
OME-A-822PGL/PGH Hardware Manual ---- 36