Choosing a Pressure Sensor John Pocreva MannKind Corp #AdvMfgExpo
Introduction Consider a device to measure inhalation pressure through a dry powder inhaler Technology implemented in both Acoustic and Direct reading modes Original design was tabled in 2010 Project restarted in Early 2016 #AdvMfgExpo
Mannkind DPI Platform Unique high resistance dry powder inhaler Requires a minimal threshold for reliable operation Has multiple dosage strengths Reusable yet disposable inhaler, single use dose cartridges
Mannkind Inhaler Both the BluHale Device and Inhaler shown separately
MannKind Inhaler with BluHale Jacket attached
Mannkind BluHale Technology Device to measure and qualify patient inhalation effort Uses Bluetooth Low Energy to transmit an inhalation signal to a Phone, Tablet or PC Attaches to the disposable inhaler and is removed and reused
Mannkind Dreamboat Inhaler Inhaler with Demo Cartridge Demo Cartridge Installed
Typical Inhalation Profile
Android Profile Example
Electroacoustic Signal Path Mic HPF RMS- DC + - A/D RF/BLE UI CPU
Differential Pressure Signal Path Diff I2C CPU RF/BLE UI Pressure Abs Real Time OS LCD Display
Acoustic Measurements Uses a Microphone to sample sound pressure in the vicinity of the mouthpiece airway Is sensitive to variations in the airway Sensitive to ambient noise
How can we improve on this? We are trying to measure pressure Not sound Perhaps there is a pressure sensor that will work Google Search
Direct Pressure Measurements Starting with the MS5608 we attached SMT pressure sensors to the inhaler and ran tests Even in early trials the results were demonstrably better than acoustic pressure measurements
Pressure Sensor Specifications Part SDP31X MS5611 MS5805 Comm Protocol I2C I2C or SPI I2C Range 500Pa Diff 10 1200mBar Absolute 10 2000 mbar Accuracy 3% +-1.5 mbar +- 2 mbar ADC 16 Bit 24 Bit 24 bit Conversion time 0.5 ms 8.2 ms 16.44 ms
Analog or Digital? Analog Sensor would limit A/D resolution to 12 bits Digital Sensors would provide 16 and 24 Bit resolution plus noise immunity
0 to 6 kpa in 150ms Bandwidth This equates to a critical frequency of 40 Hz requiring a 25 ms sample interval
Accuracy Target final accuracy of 10% of reading Criteria for accuracy determination include known inhaler resistance and known pressure drop
Dynamic Range 0 to 6 kpa at the mouthpiece will equate to around 0 to 0.5kPa at the inlet A sensor that has at least a 500Pa range will suffice More is not necessarily better
Resolution The minimum pressure that can be resolved a function of both sensing technology and data conversion circuitry When all is said our resolution actually is about 0.023 kpa
Strain gage Mass Flow Thermistor Pt RTD Sensing Technology
Physical Constraints BluHale Jacket Solid Model
1.Prototypes First test of the Absolute Variometer Sensor
First iteration with MS5611 Sensor The MS5608 Sensor installed for the first time.
2.Prototypes First test of the Absolute Variometer Sensor Variometer actually on main board model
MS5611 Barometric Pressure Sensor
3.Prototypes First test of the Absolute Variometer Sensor Variometer actually on main board model Uh oh, Variometer doesn t really work?
Variometer is too sensitive
4.Prototypes First test of the Absolute Variometer Sensor Variometer actually on main board model Uh oh, Variometer doesn t really work? Differential Mass Flow sensor
SDP31 Sensor
5.Prototypes First test of the Absolute Variometer Sensor Variometer actually on main board model Uh oh, Variometer doesn t really work? Differential Mass Flow sensor Variometer Differential Mass Flow combo
And what you have all been waiting for BluHale 3.0
6.Prototypes First test of the Absolute Variometer Sensor Variometer actually on main board model Uh oh, Variometer doesn t really work? Differential Mass Flow sensor Variometer Differential Mass Flow combo Yay! It finally works
Response Value Typical Response Curve 250.00 BluHale Response 200.00 y = -0.4781x 2 + 38.043x + 0.6767 R² = 0.9999 150.00 100.00 50.00 0.00 0 1 2 3 kpa 4 5 6 7
Acknowledgements Dennis Overfield Brendan Laurenzi Benoit Adamo Don Ridley Cindy Elliman Spencer Kinsey Chad Smutney Jason Van Anden