Service manual

IQmark Digital Spirometer Operation Manual
94
Theory of Operation
The IQmark Digital Spirometer Handle or data acquisition module is a self contained module
for the acquisition and digitalization of pressure data acquired via the DPM. The IQmark
Digital Spirometer operating principals are that of the Fleisch Pneumotach.
The Disposable Pneumotach Mouthpiece
The Pneumotach, also known as the flow sensor, mouthpiece or DPM, is a single piece low
cost disposable device. Its primary components are the pressure ports, mouthpiece and
laminar flow element (LFE). During pulmonary function testing (PFT) air is expelled and
travels through the LFE. The LFE smoothes the airflow and provides a consistent resistance
in the path of the air. Two pressure ports sense pressure changes on either side of the LFE.
The pressure ports are connected to a precision differential pressure transducer. The
differential pressure signal is digitized and sent via the serial port to the Spirometry program
running on the PC. The Spirometry program computes flow using the pressure data then
calculates volume by integrating flow data over time.
IC Pressure Transducer
A precision piezio electric transducer takes differential pressure measurements from the
disposable pneumotach mouthpiece. Differential measurements produce more accurate
results as opposed to comparing a single measurement to estimated ambient air pressure.
Handle Orientation Compensation Circuit
An orientation compensation circuit stabilizes the Spirometer during PFT testing. This circuit
eliminates artifacts generated by motion in the X, Y and Z axis as well as allowing a short
enclosed hose path from the pneumotach to the transducer.
16 bit A/D
The A/D converter used is a programmable 2 channel Sigma Delta 16 bit A/D converter. The
A/D converter provides the 12Hz low pass filtering for the Spirometry pressure signal. The
effective sampling rate is 48 Hz. The digitized pressure signal is sent serially to the micro
controller.
Temperature Sensor
An LM34 temperature sensor relays ambient temperature information to the Spirometer
program. Ambient temperature is utilized to produce more accurate BTPS calculations. The
A/D converter converts the temperature signal when the Spirometer handle is powered up
and then passes it along to the Spirometer program through the micro controller and serial
interface.
Micro controller
The micro controller is a PIC16C66 chip produced by Microchip Technology. The micro
controller receives the digitized data from the A/D converter, temperature sensor, low battery
Next
Back
Go To Table Of Contents