High Precision ADC Selection and Applications

Amazeng Technical Team
10 min read
ADCAnalogMeasurementSensorsPCB Design

Importance of ADC in Precision Measurement

In industrial measurement systems, choosing the right ADC (Analog-Digital Converter) directly affects system performance. 24-bit resolution offers the ability to measure at the microVolt level.

ADC Performance Criteria

Resolution vs. Effective Number of Bits (ENOB)

The difference between theoretical resolution and actual performance is critical:

  • 24-bit resolution: 16,777,216 discrete levels
  • ENOB: Effective resolution reduced by noise and distortion

Sampling Rate

Typically 1kHz sampling rate is used in industrial applications:

f_sample = 1kHz
T_sample = 1ms
Nyquist Frequency = 500Hz

Signal Conditioning

Anti-Aliasing Filter

Analog filtering before sampling is mandatory:

f_cutoff = 0.4 * f_sample = 400Hz (for 1kHz)
Filter Order: 4th order Butterworth

Reference Voltage Stability

Ultra-low drift reference for precision measurements:

  • Drift: < 2ppm/°C
  • Noise: < 10µVrms
  • Long-term stability: < 50ppm/1000hr

Loadcell Application

Example 2mV/V loadcell reading circuit commonly used in industrial weighing systems:

// 10V excitation, 2mV/V loadcell
// Full scale: 20mV
// 24-bit ADC: 2.5V reference
// Gain: 2.5V / 20mV = 125

#define ADC_REF_VOLTAGE 2.5
#define LOADCELL_SENSITIVITY 2.0  // mV/V
#define EXCITATION_VOLTAGE 10.0   // V
#define PGA_GAIN 125

float calculate_weight(uint32_t adc_value) {
    float voltage = (adc_value / 16777216.0) * ADC_REF_VOLTAGE;
    float loadcell_mv = (voltage / PGA_GAIN) * 1000;
    float weight_kg = loadcell_mv / (LOADCELL_SENSITIVITY * EXCITATION_VOLTAGE);
    return weight_kg * calibration_factor;
}

4-20mA Current Loop Reading

Industrial sensor standard:

I_min = 4mA  → Sensor minimum
I_max = 20mA → Sensor maximum
R_shunt = 250Ω

V_min = 4mA × 250Ω = 1V
V_max = 20mA × 250Ω = 5V

Calibration and Linearization

Two-Point Calibration

# Zero calibration
zero_reading = adc.read()

# Span calibration (known weight)
span_reading = adc.read()
span_weight = 10.0  # kg

gain = span_weight / (span_reading - zero_reading)
offset = -zero_reading * gain

Temperature Compensation

float temp_coefficient = -0.002;  // %/°C
float reference_temp = 25.0;      // °C
float current_temp = read_temperature();

float temp_correction = 1.0 + temp_coefficient * (current_temp - reference_temp);
float corrected_value = raw_value * temp_correction;

PCB Layout Recommendations

  1. Analog Ground Plane: Separate from digital, single point connection
  2. Kelvin Connection: For 4-wire measurement
  3. Guard Rings: Preventing leakage currents
  4. Component Placement: Reference and filter components close to ADC

EMI/EMC Protection

EMI protection is critical in industrial environments:

  • Differential Input: Common mode noise suppression
  • RC Filtering: 1kΩ + 100nF at ADC input
  • Shielded Cable: Twisted pair, shield grounded
  • Ferrite Beads: At power inputs

Conclusion

High precision ADC selection and implementation requires careful design and calibration. By applying these principles, industry-standard precision can be achieved.

With over 10 years of experience in precision measurement systems design, Amazeng offers customized solutions for you.

Back to All Posts