Remaining ScheduleToday: Group presentations, intro to electricity (LAST DAY TO DROP WITH A W is 5-11)

5-16-14: QUIZ 5 Finish Electricity

5-23-14 QUIZ 6: REVIEW of material PART 1 (weeks 1-6)

5-30-14 QUIZ 7, REVIEW of material PART 2 (weeks 7-13)

6-7-14: Final exam/Cumulative (50 points)

Two lowest quiz grades will be droppedFinal Exam study guide will be given out next week

Electricity and MagnetismRT 21

Introduction•Electricity is a form of energy•The electron is the primary charge carrier in electrical circuits involving metal wires because it is the lightest and most mobile of the subatomic particles. The electron has one unit of negative charge. A negatively charged body has an excess and positively charged body has a deficiency of electrons

Coulomb's Law Describs the electrostatic interaction between electrically charged particles The force between two charged particles is directly proportional to the product of their charges and inversely proportional to the distance between them. Like charges repel and unlike charges attract http://www.youtube.com/watch?v=rYjo774UpHI

ConductorA substance that provides little resistance to the flow of electrons, Ex: metalsSome examples of conductors are:CopperAluminumPlatinumGoldSilverWaterPeople and AnimalsTrees

Insulator A substance that provides high resistance to the flow of electrons Some examples of insulators are: Glass

Porcelain

Plastic

Rubber Electricity will always take the shortest path to the ground. Your body is 60% water and that makes you a good conductor of electricity. If a power line has fallen on a tree and you touch the tree you become the path or conductor to the ground and could get electrocuted.

The rubber or plastic on an electrical cord provides an insulator for the wires. By covering the wires, the electricity cannot go through the rubber and is forced to follow the path on the aluminum or copper wires.

Semiconductor A substance that offers intermediate resistance to the flow of Electrons. Ex: silicon A semiconductor is a material which has electrical conductivity between that of a conductor such as copper and that of an insulator such as glass.

Semiconductors are the foundation of modern electronics, including transistors, solar cells, light-emitting diodes (LEDs), quantum dots and digital and analog integrated circuits. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of electrons inside a lattice of atoms.

The conductivity of a semiconductor material increases with increasing temperature, behavior opposite to that of a metal. Semiconductors can display a range of useful properties such as passing current more easily in one direction than the other, variable resistance, and sensitivity to light or heat. Because the conductive properties of a semiconductor material can be modified by controlled addition of impurities or by the application of electrical fields or light, devices made with semiconductors are very useful for amplification of signals, switching, and energy conversion.

Coulomb The SI (System Internationale) unit for electrical charge is the coulomb, which is the amount of charge that flows through a 120 watt, 120 volt light bulb each second. The flow of electric charge or charge/time is called current and the standard unit of current is the ampere or amp which is 1 coulomb of charge per second.

Coulomb’s Law The interaction between charged objects is a non-contact force that acts over some distance of separation. Charge, charge and distance. Every electrical interaction involves a force that highlights the importance of these three variables. Whether it is a plastic golf tube attracting paper bits, two like-charged balloons repelling or a charged Styrofoam plate interacting with electrons in a piece of aluminum, there is always two charges and a distance between them as the three critical variables that influence the strength of the interaction.

Ohm's law Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship

The relationship between voltage, current, and resistance: Amps = Volts / Ohms.

Ohm’s Law The Ohm is the unit of electrical resistance; the Ampere is the unit of electrical current or flow of electrons; the volt is the unit of electrical energy or pressure.

Example: A circuit powered by a 12 volt battery has a resistance of 3 ohms. What is the current flowing through the circuit?

Amps = Volts / Ohms Amps = 12/3 = 4 Amps

Ohm’s Law Ohm's law can be rearranged to solve for the unknown value, so ---

Ohms = Volts / Amps and Volts = Amps x Ohms

Electrical PowerElectric power is the rate at which electric energy is transferred by an electric circuit.

The law of electrical power is the relationship between watts, current and volts:

Watts= Volts x Amps

Example: An 10 amp electrical circuit is operating at 120 volts. What is the electrical power of the circuit?

Watts = 10 x 120 = 1200 Watts

the power equation can be rearranged to solve for the unknown value, so - - -Volts = Watts / Amps and Amps = Watts / Volts

Electrical Circuits Components of an electrical circuit can be connected in many different ways.

The two simplest of these are called series and parallel and occur very frequently.

Components connected in series are connected along a single path, so the same current flows through all of the components

Components connected in parallel are connected so the same voltage is applied to each component

Series Circuit 1. The electric current must pass through all resistors in the circuit.

2. The equivalent resistance, of the circuit, is obtained by adding the resistances and the equivalent resistance will be the sum of the resistances in the circuit.

3. If one resistor (lamp) in the circuit fails, the others will fail.

4. There is only one path for the current to travel.

5. The more resistors there are in the circuit, the greater the total resistance in the circuit.

Parallel Circuit 1. The electric current passes through just one of resistors in the circuit.

2. The equivalent resistance, of the circuit, is obtained by adding the reciprocals of each resistance and the equivalent resistance will be less than that of the lowest resistor in the circuit.

3. If one resistor (lamp) in the circuit fails, the others will continue to operate.

4. There is more than one path for the current to travel.

5. The more resistors there are in the circuit, the lower the total resistance in the circuit.

Fuse, circuit breaker and ground wire

The fuse or circuit breaker is a fire protective device, while the ground wire provides protection from shock.

Fuses and breakers limit the current which can flow in a circuit. The metal filament in the fuse melts and breaks the connection, whereas in a breaker, the heating effect on a bimetallic strip causes it to bend and trip a spring-loaded switch.

Fuse, circuit breaker and ground wire

The term "ground" refers to a connection to the earth, which acts as a reservoir of charge.

A ground wire provides a conducting path to the earth which is independent of the normal current-carrying path in an electrical appliance. As a practical matter in household electric circuits, it is connected to the electrical neutral at the service panel to guarantee a low enough resistance path to trip the circuit breaker in case of an electrical fault

Attached to the case of an appliance, it holds the voltage of the case at ground potential (usually taken as the zero of voltage). This protects against electric shock. The ground wire and a fuse or breaker are the standard safety devices used with standard electric circuits.

Alternating (AC) and Direct (DC) current

Alternating current changes direction of flow while direct current flow is one direction. Household current is AC and automobile and current from battery powered devices is DC.

Electricity flows in two ways: either in an alternating current (AC) or in a direct current (DC). Electricity or 'current' is nothing more than moving electrons along a conductor, like a wire, that have been harnessed for energy. Therefore, the difference between AC and DC has to do with the direction in which the electrons flow. In DC, the electrons flow steadily in a single direction, or "forward." In AC, electrons keep switching directions, sometimes going "forward" and then going "backward."

Alternating Circuit Direct Current

Amount of energy that can be carried Safe to transfer over longer city distances and can provide more power.

Voltage of DC cannot travel very far until it begins to lose energy.

Cause of the direction of flow of electrons Rotating magnet along the wire. Steady magnetism along the wire.

FrequencyThe frequency of alternating current is 50Hz or 60Hz depending upon the country.

The frequency of direct current is zero.

Direction It reverses its direction while flowing in a circuit. It flows in one direction in the circuit.

Current It is the current of magnitude varying with time It is the current of constant magnitude.

Flow of Electrons Electrons keep switching directions - forward and backward.

Electrons move steadily in one direction or 'forward'.

Obtained from A.C Generator and mains. Cell or Battery.Passive Parameters Impedance. Resistance onlyPower Factor Lies between 0 & 1. it is always 1.

Types Sinusoidal, Trapezoidal, Triangular, Square. Pure and pulsating.

Example The electrical capacity, in watts, of a household electrical circuit is the amp rating of its fuse times the voltage, ie 120 volts. For a 15 amp line it is 15 amps x 120 volts = 1800 watts. To determine how many light bulbs could be used on this circuit divide the wattage of the bulbs into the capacity of the line.

Transformers Transformers are used to change voltage. The can either increase the voltage or decrease the voltage.

A transformer is an electrical device that transfers energy between two circuits through electromagnetic induction. A transformer may be used as a safe and efficient voltage converter to change the AC voltage at its input to a higher or lower voltage at its output. Other uses include current conversion, isolation with or without changing voltage and impedance conversion.

Wheatstone Bridge The Wheatstone Bridge is an electrical circuit that is used to measure an unknown electrical resistance by comparing it to known resistances by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Medical example is an oxygen analyzer.

When the bridge is connected in an electrical circuit, part of the current flows to the object whose resistance is unknown and part flows to the resistor of known resistance. If more current flows through one side of the circuit than the other, the galvanometer shows the difference. The sliding contact is then moved along the wire until current flows equally along both sides of the bridge and the galvanometer shows zero.

When the bridge is thus balanced, the unknown resistance is calculated by a formula. The formula is: X = RD'/D (X is the unknown resistance. R is the known resistance. D is the distance from the key to the right end of the meter stick. D' is the distance from the key to the left end.)

http://www.youtube.com/watch?v=Kf5XkK0465A

Voltage, Current, Electricity, Magnetism http://www.youtube.com/watch?v=XiHVe8U5PhU

HOSPITAL ELECTRICAL SAFETY

The usual cause of death from electrical shock is ventricular fibrillation. The harmful effects of electricity are determined by: 1) the amount of electric current that flows through the body 2) the duration of the current flow -- this is why static electricity is not a shock hazard, it is very short duration

3) the current is the primary variable which determines the seriousness of a shock and the current depends on the voltage and resistance. The resistance of the body (skin) is very variable and thus is the most important factor that determines the severity of an electrical shock.

HOSPITAL ELECTRICAL SAFETY

A shock hazard occurs when electric current passes through a person. Shocks range in severity from painful, but otherwise harmless, to heart-stopping lethalityDefinition of microshock: The passage of electrical current down a conducting material directly to the myocardium.Many hospitalized patients are "microshock sensitive" because they have a direct, low-resistance pathway to the heart. In patients who are microshock sensitive, a charge of 1/2000 to 1/5000 lower will cause death.

HOSPITAL ELECTRICAL SAFETY

Electrical currents through people produce tremendously varied effects. An electrical current can be used to block back pain. The possibility of using electrical current to stimulate muscle action in paralyzed limbs, perhaps allowing paraplegics to walk, is under study.

A pacemaker uses electrical shocks to stimulate the heart to beat properly.

An electric current can cause muscular contractions with varying effects. (a) The victim is “thrown” backward by involuntary muscle contractions that extend the legs and torso. (b) The victim can’t let go of the wire that is stimulating all the muscles in the hand. Those that close the fingers are stronger than those that open them.

HOSPITAL ELECTRICAL SAFETY

The 6 major measures of hospital electrical safety are:

A. Ground all equipment that is near the patient.

B. Do not ground the patient.

C. Bare metal cases of electrical equipment should be kept out the patient's reach.

D. All points of patient contact of electrically operated equipment should be electrically insulated from the metal case of the equipment.

E. Avoid contact with bare pacemaker wires or conductive catheters with touching electrical equipment.

F. Connect all equipment to be used on the microshock sensitive patient to electrical receptacles that have a low resistance ground.

All appliances/equipment (outside equipment brought in) used in the hospital must be inspected by Biomedical to ensure safety

Most hospitals do not allow patients to use their own electrical devices because they may not be electrically safe -- that is have a functioning ground wire.

Static electricity Static electricity is an instantaneous, high voltage discharge that represents very tiny amounts of energy, will produce a momentary sensation of shock. Static electricity is not a dangerous shock hazard because it does not produce a significant current through the body. The major danger of static electricity in hospitals is the spark can cause an explosion or fire if the spark comes in contact with flammable liquids or gases.

MEDICAL ELECTRICAL DEVICES

The three electrical temperature measurement devices or sensors commonly used in medical equipment are the thermocouple, the electrical resistance thermometer, and the thermistor.

The thermocouple uses the contact voltage of two different metals to measure temperature. examples are electric oral and rectal fever thermometers.

MEDICAL ELECTRICAL DEVICES

The electrical resistance thermometer (ERT) measures temperature based upon its relationship with electrical resistance.

Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is usually quite fragile, so it is often placed inside a sheathed probe to protect it. The RTD element is made from a pure material, typically platinum, nickel or copper. The material has a predictable change in resistance as the temperature changes and it is this predictable change that is used to determine temperature.

MEDICAL ELECTRICAL DEVICES

A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors.

Thermistors are widely used as temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements.

The thermistor is similar to the ERT but decrease the resistance as the temperature increases. example is an oxygen analyzer that must provide an accurate reading in environments with different temperatures.

MEDICAL ELECTRICAL DEVICES

A Transducer is a sensing device that changes one kind of energy to another kind of energy. A pressure transducer changes pressure energy to electrical energy.

MEDICAL ELECTRICAL DEVICES

The two main kinds of pressure transducers are strain gauge and piezoelelectric.

A strain gauge is a device used to measure strain on an object. The most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.

Seen in radiology equipment, medical pumps/blood pressure measurements….

MEDICAL ELECTRICAL DEVICES

Piezoelelectric: The conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy is the basis for ultrasonic testing.

Use in RT: Ultrasonic Nebulizers The active element is the heart of the transducer as it converts the electrical energy to acoustic energy, and vice versa. The active element is basically a piece of polarized material (i.e. some parts of the molecule are positively charged, while other parts of the molecule are negatively charged) with electrodes attached to two of its opposite faces. When an electric field is applied across the material, the polarized molecules will align themselves with the electric field, resulting in induced dipoles within the molecular or crystal structure of the material

MEDICAL ELECTRICAL DEVICES

The oximeter is an example of a sensing device that uses light, specifically light absorption or reflection.

a sensor is placed on a thin part of the patient's body, usually a fingertip or earlobe, or in the case of an infant, across a foot. Light of two wavelengths is passed through the patient to a photodetector. The changing absorbance at each of the wavelengths is measured, allowing determination of the absorbances due to the pulsing arterial blood alone, excluding venous blood, skin, bone, muscle, fat, and (in most cases) nail polish

MEDICAL ELECTRICAL DEVICES Electrodes are used to measure pH, PCO2 & PO2 of the blood rather than direct chemical analysis because they will give a more accurate reading with a smaller sample and require less technical skill.

pH measurement◦ glass electrode◦ reference electrode◦ specimen put in a capillary tube surrounded by buffer solution◦ the tube is made of pH sensitive glass across which a potential difference is generated, which is

proportional to the pH

MEDICAL ELECTRICAL DEVICES

PCO2 measurement◦ modified glass electrode◦ comprises of a glass pH electrode that is permeable to CO2◦ CO2 diffuses from the specimen into the HCO3- solution where it dissociates with a change in pH which

is measured by the electrode◦ potential difference is proportional to CO2 concentration

PO2 measurement◦ Clark electrode or polargraphic electrode◦ O2 molecules diffuse across a plastic membrane to small platinum or gold 2nm diameter wire cathode

in a glass rod immersed in a phosphate buffer with KCl◦ O2 reduced by 2 hydroxyl ions by 4 electrons after application of 600-800mV

Arterial Blood GasesEquipment

Electronic circuitry◦ Takes electrical current changes produced in the electrodes and provides a visual display

Electrolyte Solution◦ Helps to promote chemical reactions and electrical current

Arterial Blood GasesEquipment

Electrodes ◦ Utilized to measure values of ABG

pH, PCO2, PO2

All other blood gas values are calculated

Arterial Blood GasesEquipment

pH Electrode◦ Sanz Electrode

Consists of two electrodes:

◦ sampling/measuring electrode◦ reference electrode and electrolyte solution

Arterial Blood GasesThe pH electrode is a microelectrode, shown here with its plastic jacket. At the tip is a silver-silver chloride wire in a sealed-in buffer behind PH-sensitive quartz glass. The reference electrode contains a platinum wire in calomel paste that rests in a 20% KCL solution. The blood sample is introduced in such a way that it contacts the measuring electrode tip and the KCL. A voltmeter measure the potential difference across the sample, which is proportional to the pH

Sanz Electrode (pH)

Arterial Blood GasesEquipment

PCO2 Electrode◦ Severinghaus Electrode

◦ May also be referred to as a modified Sanz electrode

Arterial Blood GasesThe PCO2 electrode is a modified pH electrode. The electrode has a sealed-in buffer; an Ag-AgCl reference band is the other half-cell. The entire electrode is encased in Lucite jacket filled with bicarbonate electrolyte. The jacket is capped with a Teflon membrane that is permeable to CO2. A nylon mesh covers the pH-sensitive glass, acting as a spacer to maintain contact with the electrolyte. CO2 diffuses through the Teflon membrane, combines with electrolyte, and alter the pH. The change in pH is displayed as partial pressure of CO2.

Severinghaus Electrode(PCO2)

Arterial Blood GasesEquipment

PO2 Electrode◦ Clark Electrode

◦ May also be referred to as a polarographic electrode

◦ Periodic/routing cleaning of the tip with pumice is required because polypropylene attracts protein

Arterial Blood GasesThe PO2 electrode contains a platinum cathode and a silver anode. The electrode is polarized by applying a slightly negative voltage of approximately 630 mV. The tip is protected by a polypropylene membrane that allows O2 molecules to diffuse but prevents contamination of the platinum wire. O2 migrates to the cathode and is reduced, picking up free electrons that have come from the anode through a phosphate-potassium chloride electrolyte. Changes in the current flowing between the anode and cathode result from the amount of O2 reduced in the electrolyte and are proportional to partial pressure of O2.

Clark Electrode (PO2)

Arterial Blood GasesCalibration Procedures

To assure appropriate electronic function of the electrodes, calibration procedures are performed

◦ Performed automatically every 30 minutes by the ABG machine◦ Performed on the pH, PCO2, PO2 electrodes◦ Specific procedure for each electrode

Arterial Blood GasesCalibration Procedures

◦ 2-Point Calibration◦ A “low” concentration and a “high” concentration is used at both ends of the

physiological range to be measured

◦ Multiple-Point Calibration (3 or more points)

◦ Verifies whether the gas analyzer is linear or not

Arterial Blood GasesCalibration Procedures

pH Electrode

◦ Uses two specific buffers with approximate values of:

◦ 6.840 buffer◦ referred to as the zero point or low point buffer

◦ 7.384 buffer◦ high point or slope point buffer

Arterial Blood GasesCalibration Procedures

pH Electrode

◦ Each buffer is injected into the sample chamber, one at a time

◦ The values of the buffer that is injected, should be displayed on the ABG machine within a specific SD (standard deviation)

Arterial Blood GasesCalibration Procedures

pH Electrode

◦ Standard deviation for pH is + .005

◦ If value displayed is within the SD, machine is electronically calibrated

◦ If value displayed is outside of the SD, machine needs to be adjusted to assure electronic function

Arterial Blood GasesCalibration Procedures

PO2 & PCO2 Electrode

◦ Uses two specific concentration of gases for each electrode with approximate concentrations of CO2 and O2

◦ Uses two different tanks of gas to accomplish this