1. Analog Sensing 101 WITH P14452

2. Agenda  Analog Signal Characteristics  Common Problems with A/D Conversion  Clipping  Small Signals  Aliasing  Analog Signal Conditioning  “Digital” Sensors

3. Analog Signal Characteristics  Two Key Parameters  Voltage Range  i.e. +/- 50V  Frequency Range  i.e. < 5 KHz

4. Common Problem: Clipping  Cause:  A/D Converter is unable to record voltages outside of operating range (i.e. 0-5V)  Solution:  Attenuation  Reduce the voltage range of the signal, without corrupting the information  Scale (in software) the digital representation to reflectthe true value

5. Common Problem: Small Signals  Cause:  Analog Signal has a voltage range much lower than that of the A/D converter  Solution:  Amplification  Increase the voltage range of the signal, without corrupting the information  Scale (in software) the digital representation to reflect the true value

6. Common Problem: Aliasing  Cause:  Violation of the Nyquist limit by  Incorrect sampling frequency  High Frequency Signal Noise  Solution:  Low Pass Filter  Remove all frequencies above the frequency range of the sensor before capture of the signal

7. Analog Signal Conditioning  Process:  Attenuate Large Signal  Amplify Small Signal  Convert Differential Signal to Single Ended Signal  Apply DC Bias  Remove High Frequencies  Convert to Digital Value  Scale Digital Value according to:  Attenuation  Amplification  DC Bias  Conversion Factor ( i.e. Celsius / mV )

8. “Digital” Sensors  What are they?  Analog Sensor with Signal Conditioning and A/D conversion in the same package  Advantages  Standard Communication Protocol  i.e. I2C, SPI, CAN  Preset to Optimally Condition and Sample  Minimized PCB Requirements  Inexpensive  Accurate  Disadvantages  Software Requirement  Typically Fixed Sampling Rate

9. Case Study: Temperature Sensor ADT7301  Temperature Range  -40 C to 150 C  Accuracy  +/- 0.5 C  Precision  13-bit  0.03125 C / 1 bit increase  Max Sampling Rate  83.33 Hz  Interface  SPI  2.7-5.25V Supply  Cost: ~$1.21 OMEGA TTIN-18 Type T Thermocouple  Temperature Range  -185 C to 300 C  Additional Components Needed  Instrumentation Amplifier  INA128 - $11.30  Low Pass Filter  3 Op-AMPS  LM741 - $0.70  Analog to Digital Converter  Cost: $21 + $11.30 + $2.10 = $33.40

10. Case Study: Pressure Sensor Honeywell SSCDANN150PG2A3  Pressure Range  0 – 150 PSIG  Accuracy  +/- 1% (2% band)  Precision  14-bit  0.0092 PSI / 1 bit increase  Max Sampling Rate  ~2 kHz  Interface  I2C  3.3V or 5V Supply  Cost: ~$36 Ashcroft G17M0242F2200#  Pressure Range  0 – 200 PSI  Accuracy  +/- 0.5%  Voltage Supply: 9-24V  Additional Components Needed  Attenuator (2 Op-amps) ~$1.40  Instrumentation Amplifier ~$11.30  Low Pass Filter (3 Opamps) ~$2.10  Analog to Digital Converter  Cost: $175.50 + $20.80 = $196.30

11. Case Study: Vibration Sensor Freescale Xtrinsic MMA8451Q 3-axis  Vibration Range  +/- 8g  Accuracy  +/- 1% (2% band)  Precision  14-bit  0.000977g / bit  Max Sampling Rate  =< 800Hz  Interface  I2C  1.95V to 3.6V Supply  Cost: ~$1.67 Omega ACC310 1-axis  Vibration Range  +/- 75g  Precision: 100mV/g  Output Range: +/- 7.5V  Voltage Source: 24-36V  Additional Components Needed  Attenuator (2 Op-amps) ~$1.40  Instrumentation Amplifier ~$11.30  Low Pass Filter (3 Opamps) ~$2.10  Analog to Digital Converter  Cost: $175 + $20.80 = $195.80