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ADS-929GM Arkusz danych(PDF) 4 Page - List of Unclassifed Manufacturers |
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ADS-929GM Arkusz danych(HTML) 4 Page - List of Unclassifed Manufacturers |
4 / 8 page ® ® ADS-929 4 CALIBRATION PROCEDURE (Refer to Figures 2 and 3) Any offset and/or gain calibration procedures should not be implemented until devices are fully warmed up. To avoid interaction, offset must be adjusted before gain. The ranges of adjustment for the circuit of Figure 2 are guaranteed to compensate for the ADS-929's initial accuracy errors and may not be able to compensate for additional system errors. All fixed resistors in Figure 2 should be metal-film types, and multiturn potentiometers should have TCR’s of 100ppm/°C or less to minimize drift with temperature. A/D converters are calibrated by positioning their digital outputs exactly on the transition point between two adjacent digital output codes. This can be accomplished by connecting LED's to the digital outputs and adjusting until certain LED's "flicker" equally between on and off. Other approaches employ digital comparators or microcontrollers to detect when the outputs change from one code to the next. For the ADS-929, offset adjusting is normally accomplished at the point where the MSB is a 1 and all other output bits are 0's and the LSB just changes from a 0 to a 1. This digital output transition ideally occurs when the applied analog input is +½ LSB (+305µV). Gain adjusting is accomplished when all bits are 1's and the LSB just changes from a 1 to a 0. This transition ideally occurs when the analog input is at +full scale minus 1½ LSB's (+4.999085V). INPUT VOLTAGE ZERO ADJUST GAIN ADJUST RANGE +½ LSB +FS –1½ LSB ±5V +305µV +4.999085V Table 1. Zero and Gain Adjust OUTPUT CODING INPUT RANGE BIPOLAR MSB LSB ±5V SCALE 11 1111 1111 1111 +4.99939 +FS –1 LSB 11 1000 0000 0000 +3.75000 +3/4 FS 11 0000 0000 0000 +2.50000 +1/2FS 10 0000 0000 0000 0.00000 0 01 0000 0000 0000 –2.50000 –1/2FS 00 1000 0000 0000 –3.75000 –3/4FS 00 0000 0000 0001 –4.99939 –FS +1 LSB 00 0000 0000 0000 –5.00000 –FS Table 2. Output Coding Figure 3. Typical ADS-929 Connection Diagram Zero/Offset Adjust Procedure 1. Apply a train of pulses to the START CONVERT input (pin 16) so the converter is continuously converting. If using LED's on the outputs, a 200kHz conversion rate will reduce flicker. 2. Apply +305µV to the ANALOG INPUT (pin 20). 3. Adjust the offset potentiometer until the output bits are a 1 and all 0's and the LSB flickers between 0 and 1. Gain Adjust Procedure 1. Apply +4.999085V to the ANALOG INPUT (pin 20). 2. Adjust the gain potentiometer until the output bits are all 1's and the LSB flickers between 1 and 0. Figure 2. ADS-929 Calibration Circuit Coding is offset binary; 1LSB = 610µV. 13 ADS-929 14 20 16 18 17 12 11 10 9 8 7 6 5 4 3 2 1 15 BIT 1 (MSB) BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8 BIT 9 BIT 10 BIT 11 BIT 12 BIT 13 BIT 14 (LSB) EOC ANALOG INPUT START CONVERT 19, 23 22 24 0.1µF 4.7µF +5V 0.1µF 4.7µF 0.1µF 4.7µF + + –12V/–15V +12V/+15V + 0.1µF + 4.7µF 21 +10V REF. OUT –5V to +5V DIGITAL GROUND ANALOG GROUND To Pin 20 of ADS-929 –15V SIGNAL INPUT GAIN ADJUST 1.98k Ω 50 Ω +15V 2k Ω 200k Ω 20k Ω –15V +15V ZERO/ OFFSET ADJUST |
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