Analog Terminal Board
Reference
Channel 0 Return lines. R26, need not be inserted when the CJC
circuitry is in use. When jumpers are not placed across the W1
and W2 shorting headers the cold junction compensation
circuitry does not effect the analog terminal board or the
AD1200 card at all.
The CJC circuitry produces 0.5mVolts per degree Centigrade,
thus by performing an A/D conversion on channel 0 the
temperature of the thermocouples cold junction is known and the
apparent temperature measured by the thermocouple can be
adjusted so that the true temperature of the thermocouple is
known.
Example:
AD1200 card jumper set range of 0-10 Volts unipolar.
Gain of 1000 is selected for Channel 0
Ambient temperature of 18 degrees Centigrade
Thus CJC circuit gives a voltage of 18 x 0.5 mV = 9mV.
9mV input Channel 0 at gain of 1000 equivalent to 9 Volts
9 Volts on 0-10V i/p range is 9*4096/10= 3686= E66hex
To convert a reading into a temperature in degrees Centigrade
use the following formula:-
Temp in C =
(ADC Reading * Input Span In Volts)
_______________________________
(4096 * Gain * 0.5mV per C)
where the 0.5mV per degree C is 0.5/1000 Volts per degree C.
Thus for the above ADC reading of 3686 decimal, with a 10Volt
span in the input range and a Gain of 1000.
Temp in C=
( 3686 * 10)
__________
(4096 * 1000 * 0.5/1000 )
Temp in C=
( 36860)
=
18 degress Centigrade.
_______
(2048 )
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