# RAD 214 Radiographic Equipment

 Define Generator: Converts mechanical energy into electrical energy Define motor: convert electrical energy into mechanical enery Slip rings complete the alternating circuit in simple electric generator (attached to carbon "brushes") How long does it take for one full cycle to complete in an AC generator 1/60 of a second Sine curve graph representing the sine of the angle between the plane of the armature and a plane perpendicular to the magnetic field Which pole influences the movement of the armature? North A generator must have.... a powerful electromagnetan armature a motor must have... 2 interacting magnetic fields (one created by a current carrying wire, and an existing magnetic field) Values used to define resistance in an AC circuit... Effective resistanceroot mean square (rms) value Properties of resistance in a DC circuit? MaterialLengthCross sectional areaTemperature Properties of impedence in an AC circuit.. Resistance (Material, Length, area, temp.)Inductance reactance (Lenz's Law (back emf))Capacitive reactance DC generators use _____ to complete the circuit? split-ring commutator Advantages of AC? 1. Can be transformed2. Less power loss (through heat loss) Formula for power P (watts)= V (volts) x I (amps) Formula for power loss? PL = I2R Left hand thumb rule: Thumb- direction of the electron flowfingers- wrap in the direction of the magnetic field Right hand thumb rule: Thumb- direction of the current flowfingers- wrap in the direction the magnetic field Left hand generator rule thumb- direction of the armature movementindex finger- direction of the magnetic field (S)middle finger- direction of the electron flow Right hand generator rule thumb- direction of the armature movementindex finger- direction of the magnetic field (S)middle finger- direction of the current flow Left hand motor rule thumb- direction of the armature movementindex finger- direction of the magnetic field (S)middle finger- direction of the current flow Right hand motor rule thumb- direction of the armature movementindex finger- direction of the magnetic field (S)middle finger- direction of the electron flow Three types of Electic Motors DC motorsynchronous ACinduction AC Two types of Generators AC DC Synchronous AC motor turns at the same speed as the armature of the AC generator supplying the current (or a multiple of the armatures speed) (used in clocks or timing devices) Induction AC motor uses the stationary magnets of a stator, energized in sequence by a multiphase current, to interact through the motor principle with the copper bars (wrapped around an iron core) of a rotor-uses no direct contact-used for a rotating anode Typical speed of an anode? 3500 rpm-anode always spins at the same speed Transformer -Changes the voltage of AC with no electrical contact or moving parts (electomagnetic induction principle)-no appreciable loss of electrical enery (less than 5%) Types of transformers Air coreopen coreclosed coreshell Air core transformer two insulated coils laying side by side Transformer Law VS/VP =NS/NP Voltage (emf) in the secondary coil is to the emf in the primary coil, as the # of turns in the secondary is to the # of turns in the primary Open core transformer -iron core inserted in coils of wire-experiences leakage flux (loss of magnetic flux at the ends of the iron cores) Closed core transformer -heavily insulated coils called 'windings' wrapped around a square or circular iron core-experiences transformer loss in the form of eddy currents -lamination hinders the formation of eddy currents-this is the type of transformer used for x-ray generating equipment Shell type transformer -used as commercial or power transformer-laminated silicon steel with 2 rectangular holes-windings around central portion Types of Electrical power loss -copper loss (I2R)- resistance-eddy loss-heat generated by changing electical current (reduced by lamination w/silicon steel plates)-hysteresis- heat generated by constant reorientation of magnetic dipoles (coercivity -requires energy to reorient poles [causes hysteresis] (reduced by silicone steel lamination)) Autotransformer -Varies input voltage to a transformer to control output voltage by selection of # of turns tapped on the secondary side-sets your kV-between source of AC and the primary side of the transformer-single coil serves as primary and secondary Autotransformer Law seconday voltage/primary voltage= #tapped turns /#primary turns 2 circuits of the X-ray tube? filament circuit- carries current to heat the filamenttube circuit-carries the current that passes from cathode to anode (electrodes) to produce x-rays Types of rectification (3) Self-rectifiedvacuum tube solid state Self-rectification -uses no diodes-no protection for the filament-self-half wave-single pulse-100% rippple with a pause-forward bias (useful half of the voltage cycle)-low heat loading capacity-limited to low exposure factors-100% suppression-single phase One diode rectification -half-wave-one-pulse-100% ripple w/ a pause-100% suppression-diode protects tube filament-single phase 2 diode rectification -single phase-half-wave-one- pulse-100% ripple w/pause-100% suppression-increased load capacity-increased effeciency-increased filament protection 4 diode rectification -full-wave-2 pulse-single phase-100% ripple-100% inversion-high % of low energy x-rays produced Electron flow in diodes.... from n to p Conventional electrical current flow in diodes..... from p to n What does a rectifier do? Converts AC to useable DC 3 energy bands in materials -conduction -forbidden-valence commom semi-conductor and # of valence electrons silicon; 4 e- arsenic -5 valence e--added to Si -creates donor or n-type atom-makes Si a conductor gallium -3 valence e--added to Si-creates acceptor or p-type atom-makes Si an insulator barrier voltage or potential hill the potential difference that exists between a n-type ion and a p-type ion in a diode thyristor or silicon-controlled rectifier -more complex-2 p-type and 2 n-type layer (makes 3 n-p junctions)-can hold or release large amounts of current Advantages of silicone rectifiers -compact size-no filament (means no filament transformer)-low forward voltage drop-low reverse current-long life Main switch -primary side Fuses -thin strip of metal prevents overload-primary side Autotransformer -changes voltage to set kV-primary side Pre-reading kilovoltmeter -Primary side-metering device that indicates the desired kVp Timer /Exposure switch -primary side-controls the current to the primary coil serving to complete the x-ray exposure Remote control switch -primary side-completes the circuit-protects the person making the exposure from electical shock Timer -primary side-built into the exposure switch-5 types (mechanical, synchronous, electronic, mAs, and AEC) mechanical timer -Primary-operates by clockwork-exposure time must be greater than 1/4 of a second Synchronous timer -Primary-powered by synchronous motor-minimum exposure time is 1/60 sec.-timer counts by waveform Electronic timer -primary-we use-most sophisticated-operate on variable resistance-can be use for rapid serial exposure-exposure time as small as 1 ms mAs timer/meter -secondary (b/c it monitors actual tube current)-factors time and mA to shut off at correct mAs-not really a timer AEC timer -primary-measure quantity of radiation reaching the IR to provide the required optical density Back-up timer and Minimum exposure timer -primary-terminates the exposure in the event of AEC failure-minimum exposure response time is 1 ms Circuit breaker -Primary-additional protection from overloading Filament Circuit -primary-supplies the heating current for the filament-rheostat (variable resistor) reduces current to 3-5 amp and 6-12 Volts Filament Ammeter -primary-connected in series with the filament circuit to measure current (for proper heat production w/corresponding mA)-space charge compensator automatically corrects to maitain constant mA over wide range of kV Primary coil of Transformer -primary-primary winding of the transformer Console -primary- Secondary Coil of transformer -secondary-smaller wires that primary b/c of smaller amps Miliammeter -secondary-connected in series with the high voltage/low amp secondary circuit of the transformer Rectifier -secondary-changes AC to DC-increases heating capacity permitting larger exposures Cables -secondary-hazard reduced by insulation, grounding, and grounding of the secondary winding of the step-up transformer at its mid-point x-ray tube -secondary Anode -secondary-considered part of the x-ray tube-contains stator induction motor 3 Phase Generator -6 pulse-13% ripple-12 pulse- 5% ripple-Coils are wound in delta or star pattern-primary is always delta-secondary can be delta or star-rated up to 1000 mA (kV max. 80)-exposure time down to 1 ms-nearly constant potential (small ripple) Hi-Frequency Generator -1% ripple-uses high-frequency circuit-60 Hz converted to 500-25,000 Hz-inverter circuits convert DC to square pulses-Uses an inverter module Authorjuleofthejungle ID12184 Card SetRAD 214 Radiographic Equipment Descriptionradiographic equipment Updated2010-03-28T21:03:38Z Show Answers