Background/Tutorial/FAQ

Background:
This project, building the CPAP machine, is related to mechanical and electrical engineering. It contains aspects of bio medical engineering as well; however, the building of the CPAP machine mostly relates to creating the proper electricity circuit and formulating the most efficient design of the machine.

What would happen if the motor were to fail?

Group 2 had the idea to install a second motor into the CPAP machine in case the motor were to fail and the machine would no longer operate. The two motors would be operated through a switch. The primary motor would run when the switch was flipped one way and the secondary motor would run when flipped the other. Due to shipping issues, however, this concept was not implemented in the final product.


How did the group figure out how to assemble the electrical circuit used to power the CPAP?

For building a battery-operated electrical circuit, a working knowledge of parallel and series circuit configurations and properties of direct current is essential. Circuit elements are associated with the following variables whose values depend on the elements' material composition and how they are wired together:

• Voltage (delta V), the difference in electrical potential between one end of the element and the other, which is directly proportional to the proclivity of electrons to travel across the element, measured in energy change per time (Joules per second, or Volts)
• Capacitance (C), the ability of the element to store electrons relative to voltage, measured in charge per potential difference (Coulombs per Volt, or farads)
• Current (I), the rate at which electrons are conducted, measured in charge per time (Coulombs per second, or Amperes)
• Resistance (R), the degree to which the element insulates against current, measured in potential difference per current (Volts per Ampere, or ohms)

Voltage, current, and resistance are related by the equation delta V = IR .

Different circuit elements serve different purposes:

• A capacitor stores charge. Plate capacitors have left and right plates.
• A resistor converts electrical energy into another form or forms, with some energy always leaving as heat.
• A battery or emf (voltage) source provides energy for the circuit. It has a positive terminal at a higher potential and a negative terminal at a lower potential.

("Emf" stands for "electromotive force," but this is a misnomer as potential difference is not a force. To avoid confusion, the abbreviation will be used instead of the full name.)

The terminology of circuitry is precise, and the terms "parallel," "series," "in parallel," "in series," and "in a series" can be confused if used colloquially.

• Parallel is a classification of circuit elements relative to one another. The left plates of each element are connected to one another and to one battery terminal by a conducting wire, as are the right plates to the opposite terminal.
• Series is the complement of parallel. The right plate of one element connects directly to the left plate of another element in the series.
• In parallel is a term that relates parallel elements. For instance, if element A is parallel to element B, one might say A and B are connected in parallel.
• In series complements in parallel. For instance, if A and B are distinct elements of a series (the right plate of A is connected to the left plate of B), one might say A and B are connected in series.
• In a series refers to a group of parallel elements that, as a singular unit, are connected to another element or set of elements in series. For instance, if A, B, and C are parallel, and the wire connecting them also connects directly to the right plate of element D on the left and the left plate of element E on the right, one might say that A, B, and C are altogether in a series. Relative to one another, however, they are in parallel.

Circuit elements can be connected strategically to compound their capacitance or their voltage. Parentheses denote subscripts:

• The total capacitance of a group of elements in parallel equals the sum of each element's capacitance. For n elements, C(equivalent) = C(1) + C(2) + ... + C(n).
• The reciprocal of the total capacitance of a group of elements in series equals the sum of the reciprocal of each element's capacitance. For n elements, 1/C(eq) =1/C(1) + 1/C(2) + ...            + 1/C(n).
• The total voltage of a group of elements in parallel equals each individual element's voltage. For n elements, delta V = delta V(1) = delta V(2) = ... = delta V(n).
• The total voltage of a group of elements in series equals the sum of each element's voltage. For n elements, delta V = delta V(1) + delta V(2) + ... + delta V(n).

Therefore, elements may be connected in parallel to maximize total electron storage relative to volts without increasing total voltage, or they may be connected in series to maximize voltage or emf.

What will the CPAP machine be stored in?

The materials that compose the CPAP machine will be stored in a plastic tub.

How will the user maintain the CPAP?

The battery configuration will allow the user to replace old batteries with new ones accordingly.


Source:
Serway, Raymond A., and John W. Jewett, Jr. Physics for Scientists and Engineers. Nine ed. Boston: Brooks/Cole, 2014. 746-834. Print.