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Chapter 5-6 (RT180)
physics chapters 5-6
| Question | Answer |
|---|---|
| What are the 3 major parts of the xray circuit? | 1.Low voltage operating console 2.High voltage generator 3.xray tube |
| What type of transformers are use in the xray circuit? | Autotransfomer, step up transformer, step down (filament) transformer |
| What kind of timer is used in the xray circuit? | electronic timer |
| What does a rectifier do? | coverts AC to DC |
| how many rectifiers does single phase, half-wave use? | 2 rectifiers |
| how many rectifiers does single phase, full-wave use? | 4 rectifiers |
| how many rectifiers does 3 phase, 6 pulse use? | 6 rectifiers |
| how many rectifiers does 3 phase, 12 pulse use? | 12 rectifiers |
| What is meant by single phase power? | power that ranges from zero to 120 and results in a pulsating xray beam |
| What is meant by 3 phase power? | multiple superimposed voltage wave forms, that results in nearly constant high voltage |
| Why is 3 phase more efficient than single phase? | Because it never goes to zero so its power is always constant |
| How efficient is a 3 phase, 6 pulse generator? | 87% |
| how efficient is a 3 phase, 12 pulse generator? | 96.5% |
| How many degrees out of step is each phase? | 120 degrees |
| What device is used to check timer accuracy of 3 phase equipment? | solid-state radiation detector |
| Explain a high frequency generator? | produces a nearly constant potential voltage waveform, improving image quality with lower pt dose, also very little voltage ripple |
| Explain capacitor-discharge generator? | used on portables, stores electricity, then discharges it upon taking an exposure |
| what formula is used for power rating for xray units? | watts= mA x kV KW= (mA x kVp)/1000 (single phase: multiply expression by .7) |
| What devices are used for AEC? | -currently= ionization chamber -orginally= photodiode |
| Define isotropic as it relates to the xray beam? | xrays are produced with equal intensity in all directions |
| What is the filament made of? | tungsten |
| What is meant by dual focus? | 2 filaments and 2 focal spots |
| What is the focusing cup made of and what is its function? | tungsten or molybdenum, and it focuses the electrons |
| What is meant by thermionic emission? | Is when the current passes thru the filament and literally boils off electrons |
| what is filament vaporization? | heating of the tube forms tungsten vapors inside the tube |
| What is the more prevalent cause of tube failure? | filament vaporization |
| what causes the anode to crack or pit? | excessive temps. during single exposure |
| what is the HU (heat unit) equation for single phase? | HU=kV x mAs |
| What is the HU equation for 3 phase, 6 pulse? | HU=kV x mAs x 1.35 |
| what is the HU equation for 3 phase, 12 pulse? | HU=kV x mAs x 1.41 |
| what is the HU equation for high frequency? | HU=kV x mAs x 1.45 |
| What are the 2 main circuits of the xray imaging system? | 1.high voltage/tube circuit 2.filament |
| what are the typical xray room ranges for kVp and mA? | kVp: 25-120 mA: 100-1200 |
| What does the line compensator do? | automatically keeps voltage consistent |
| What are the electrical connections on the transformers called? | Taps |
| what is the equation for the autotransformer law? | Vs/Vp=Ns/Np |
| what is the turns ratio equation? | Ns/Np |
| When you use AEC the machine sets a back-up timer to what? | 1 and 1/2 times the expected exposure time |
| What are the types of timers? | -Mechanical -Synchronous -Electronic -AEC |
| If the timer is not working properly it is usually due to what? | faulty rectifior |
| what is the maximum permissible level of leakage radiation? | 100 mR/hr at 1m |
| what is the space charge effect? | once the electrons boil off they remain in a cloud around the filament |
| what are the 2 main parts of the cathode? | filament and focusing cup |
| what are the 2 types of anodes? | stationary and rotating |
| what are the 3 types of xray tube rating charts? | 1.radiographic rating chart 2.anode cooling chart 3.housing cooling chart |
| What is directly connected to the autotransfomer? | kVp meter |