Real Time Devices AD1200 User Manual page 73

A/D Calibration
Two procedures are used to calibrate ttre AID converter for all input voltage ranges. The fint procedure cali-
brates the converter for the unipolar range (0 to +10 volts), and the second procedure calibrates the bipolarranges
(15, +10 volts). Table 5-1 shows the ideal input voltage for each bit weight for the unipolar, straight binary range,
and Table 5-2 shows the ideal voltage for each bit weight for the bipolar, twos complement ranges.
Unipolar Calibration
Two adjustments are made to calibrate+he AID converter'for.the unipolar-range of 0 to +10 vols. One is the
offset adjustment" and the other is the full scale, or gain, adjustrnent. Trimpot TR7 is used to make the offset
adjustment, and trimpot TR2 is used for gain adjustment. This calibration procedure is performed with ttre board set
up for a 0 to +10 volt input range. Before making these adjustrnents, make sure that the jumper on P3 is set for lOV
and the jumpers on P4 and Pll are set for +.
Use analog input channel 1 and set it for a gain of I while calibrating the board. Connect your precision voltage
source to channel l. Set the voltage source tD +1.22070 miltvolts, start a conversion, and read the resulting data.
Adjust trimpot TR7 until it flickers between the values listed in the table at the top of the next page. Next, set the
voltage to +9.49829 volts, and repeat the procedure, this rime adjusting TR2 until the data flickers between the
values in the table. Note that the value used to adjust the full scale volrage is not the ideal full scale value for a 0 to
+10 volt input range. This value is used because it is the maximum value at which the A,/D converter is guaranteed
to be linear, and ensures accurate calibration results.
Table 5-1 - A/D Converter Bit Wetghts,
Unipolar, Stralght Binary
A/D Bit Weight
ldeal lnput Voltage (mlllivolts)
0 to +10 Volts
1 1 1 1 1 1 1 1 1 1 1 1
+9997.6
1000 0000 0000
+5000.0
0100 0000 0000
+2500.0
0010 0000 0000
+1250.0
0001 0000 0000
+625.00
0000 1000 0000
+312.50
0000 0100 0000
+156.250
0000 0010 0000
+78.125
0000 0001 0000
+39.063
0000 0000 1000
+19.5313
0000 0000 0100
+9.7656
0000 0000 0010
+4.8828
0000 0000 0001
+2.4414
0000 0000 0000
+0.0000
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