Calibration

SCICON R&D Inc. supplies a calibration unit, CAL20, that will perform both pressure and flow calibration. The following procedures can be used to enable the display values for the DC channels to be calibrated so that they display the units of your choice very easily. By choosing a proper calibration equation, the program will automatically convert all the data values into the physical units and display them.

Flow:

- Place the oral or nasal mask on the proper adapter and hold it securely in place.

  The oral or nasal masks will naturally fit very tightly against the contour of the clear rod. To ensure a good seal, press the mask firmly against the rod, make sure that the air hole is centered in the mask. You can secure the nasal mask in place by means of the two Velcro straps.

- The oral mask base has two holes on either side. One is used for the oral mask flow measurement and the other is for making pressure records. When calibrating the airflow this hole MUST BE PLUGGED.
- An airflow control knob is provided for the masks. Turning it clockwise will decrease and completely close the valves and counter clockwise will increase and completely open the valve.
- Start the motor, and adjust the flow rate by the airflow control valve.
- The flow-tube shows airflow rate in liter per minute. Read the rate at the middle of the ball.
- To convert the rate to milliliter per second (the usual units in phonetic work), multiply the reading by 1000/60.
- Start a blank file and set the Record time to 10 seconds. Set the flow rate to a low value (say 5 l/m). While the motor is on and the ball is in the proper spot, start recording. Wait for about 5 seconds, then, while the recording is still in progress, turn off the motor. When the recording has finished, the display should look like a step with a high value at the beginning and a low value at the end. If the data looks a bit turbulent, use the lowest possible filter rate or the Analysis->Smooth menu to smooth out the data to get a smooth line.
- Start a blank log file. Place the marker at the location when the motor was off (reference level), then use Analysis->Set DC Channels Reference. This will use this point as the zero level. Then place the marker at the middle of the portion when the motor was on, use Log->Enter at marker menu to enter the value at the marker in the log file. This number corresponds to the 5 l/m of flow rate. (see figure 1)
- Repeat this process for at least 4 to 5 rate values (say 10, 15, 20, 25, and 30).
- Save and close the log file.
- Add another data point zero for 0 l/m to the data file just created. This is very important, because there should not be any flow without any displacement.
- Plot the data by hand or import the log file into any standard statistical program.
- Depending on how linear the data looks, select either a straight line going through the data points and the origin, or a quadratic function.

  If you choose a straight line, then calculate the slope of this line (see figure 2). This slope is the "B" value in the calibration equation Physiological unit = Bx + C (where C must be 0) in the Options->Channels Selection/Calibration dialog box.

- If you choose a quadratic equation, then the statistical program will give you an equation for it. Use the values for A, B and C and plug them into the proper slots in the calibration equation in the Options->Channels Selection/Calibration dialog box.

- In the unit entry slot, type in l/sec.

- Close the Options->Channels Selection/Calibration dialog box by clicking OK. Now all the data in that channel are converted into the milliliters per second.

Pressure:

- Fill half the U-tube with water. Make sure there are no bubbles in the water and the water levels are the same on both sides.

- Connect the long tubing at the end of U-tube assembly to a pressure transducer. (Channel #2 or #4).

- Open the brass air valve to the external air pressure by turning it counterclockwise a few turns.

- Pulls the syringe to half way up, making sure the water levels are still the same.

- Close the brass air valve to the external air pressure by turning it clockwise until it completely closes.

- Gently press the syringe in, moving the water column, and read the water displacement in the tube. (THE ACTUAL DISPLACEMENT IS 2 TIMES YOUR READING AS THE DIFFERENCE IN THE WATER LEVELS IS THE ACTUAL PRESSURE).
- Start a blank file and set the record time to 10 seconds. Set the water level displacement to 5 cm. Start recording. Wait for about 5 seconds, while recording still in progress, open the brass air valve to the external air pressure by turning it counterclockwise a few turns, which causes the water levels to be the same on both sides. The recorded file should now look like a step with a high value at the beginning and a low value at the end. (see figure 1 above)
- Start a blank log file. Place the marker at the location when the motor was off (reference level), then use Analysis->Set DC Channels Reference. This will use this point as the zero level. Then place the marker at the middle of the portion when the motor was on, use Log->Enter At Maker menu to enter the value at the marker in the log file. This number corresponds to the 5 cm of water pressure. (very similar to figure 1)
- Repeat this process for at least 4 to 5 values (say 5, 10, 15, and 20 cm).
- Save and close the log file
- Add another data point zero for zero cm to the data file just created. This is very important, because there should not be any pressure without any displacement.
- Plot the data by hand or import the log file into any standard statistical program.
- Depending on how linear the data looks, select either a straight line going through the data point and the origin, or a quadratic function.
- If you choose a straight line, then calculate the slope of this line (see figure 2). This slope is the "B" value in the calibration equation Physiological unit = Bx + C (where C must be 0) in the Options->Channels Selection/Calibration dialog box.
- If you choose a quadratic equation, then the statistical program will give you an equation for it. Use the values for A, B and C and plug them into the proper slots in the calibration equation in the Options->Channels Selection/Calibration dialog box.
- In the unit entry slot, type in cm/H2O.
- Close the Options->Channels Selection/Calibration dialog box by clicking OK. Now all the data in that channel are converted into the cm of water.