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Chapter 18 Electrosurgery Generators

Chapter 18 Electrosurgery Generators. 徐國恩 2014/9/15. 18-3 Electrosurgery Machines. RF generator：300 ~ 3000 kHz Active electrode： 截 面積很小( a few mm 2 )， 形成一 probe 供外科醫生操作 Passive electrode(patient plate)： 大面積(>100 cm 2) )， 放置在病患臀部或大腿下. Operating principle： 相同的電流流經不同截面積的電極，造成電流密度不同而產生不同的加熱效果

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Chapter 18 Electrosurgery Generators

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  1. Chapter 18Electrosurgery Generators 徐國恩 2014/9/15

  2. 18-3 Electrosurgery Machines • RF generator：300 ~ 3000 kHz • Active electrode：截面積很小(a few mm2)，形成一probe供外科醫生操作 • Passive electrode(patient plate)：大面積(>100 cm2))，放置在病患臀部或大腿下

  3. Operating principle：相同的電流流經不同截面積的電極，造成電流密度不同而產生不同的加熱效果 • Application：切除不良組織以及燒結出血的血管

  4. 18-4 Electrosurgery Circuits • Spard Gap Machine • T1：昇壓變壓器，使之足以使空氣離子化，一般為2000 ~ 3000 V • C1/L1：Tank circuit • L1/L2：Coupler • RFC1,RFC2：To prevent RF energy from getting into the power supply.

  5. Cut Coagulation • 一般不加 60 Hz filter 的 cut wave

  6. 18-4-1 Solid-state electrosurgery generator circuit

  7. 18-5 Electrosurgery Safety • Inappropriate points on the body：patient plate 放置處遇到凸骨、凹痕、皺紋，或是 patient plate 本身的彎曲不規則，都會產生「熱點」而引起燒傷 • Inadvertent ground path ：另外在病患身上形成接地迴路，使得電流不經由 patient plate 流出，造成燒傷 • Microscopic holes in the surgeon’s gloves • Lipuids spilled into the machine 18-3

  8. 18-6 Testing Electrosurgery Units 使用thermocouple RF ammeter： • 優點： • 本身是一 rms-reading meter，可直接反應出 output level • 不需要像 peak-reading meter 要針對輸出波形作校正 • 缺點： • 較其他儀表昂貴 • 其輸出是非線性，小功率部份判讀失準，所以甚至需要不同範圍的兩個thermocouple ammeter

  9. 使用 peak-reading meter： • Voltage divider

  10. Toroid current transformer • 普遍應用在低功率電療儀器的測試，如微燒結及眼部或內視鏡電療

  11. Chapter 19Care and Feeding of Battery-Operated Medical Equipment

  12. 19-3 Introduction Batteries are used for ： • Protability • Defibrillator • Patient monitors • ECG & blood pressure • Patient safety • Cardiac output computer

  13. 19-4 Cell or Batteries？ • The cell is the most basic element in a battery and sets the minimum voltage for that sort of device • Additional voltage is gained by connecting the cells in series, and extra current is available by connecting them in parallel • We would refer to multiple-cell entities as batteries • But in common usage, all cells and batteries are called batterise

  14. 19-5 NiCd Cells and Batteries • Most commonly used • 1.2 V terminal voltage • Sustain a charge-discharge cycle life of 1000 times before becoming unusable(the battery drops below 80% of its oribinal specified value

  15. 19-6 Battery Capacity • The capacity of a battery is measured in ampere-hours (A-H) (i.e., the product of current load , in amperes, and the time required to reach the designated discharge state) • NiCd batteries can deliver short-duration currents of 50A or more, that is why they are used in medical defibrillators and some medium-powered portable radio transmitters

  16. 19-7 Battery-charging Protocols • The general charging rule is：Charge at 1/10 ampere-hour rating for 14 hours • Fast charging should not be done unless the battery maker recommends it and be a little cautious

  17. Problems ： • Sitting：The solution for this type of problem is a trickle charge at a rate between A-H/30 and A-H/50 • Temperature effect

  18. 19-8 NiCd Battery Memory • Memory means that a battery will not allow deep discharge after repeated shallow discharges (premature failure) • A NiCd battery with memory problems can some times be reformed by repeatedly fully charging it and them immediately deep discharging it

  19. 19-9 Battery Maintenance • For most equipment the manufacturer recommends that the batteries be periodically discharged and then recharged： • 1.Fully charge the battery or cell • 2.Discharge it fully with a current of A-H/10 for 8~9 hours for multicell batteries and 10 hours for single cells (because of polarity reversal) • 3.Recharge the battery at the A-H/10 rate for 14 to 16 hours

  20. Do not leave the battery in a discharged condition for a long period, it may develop interelement shorts • Revitalization • Revitalized batteries and cells should not be regarded as reliable and should only be used for shout terms, under emergency conditions. Good engineering practice requires replacement with a new cell rather than salvaging the defective cell

  21. 19-10 Charging NiCd Batteries There are two basic forms of charger for NiCd batteries： • Constant current (CI) • The transformer secondary voltage hsould be 2.5 times (or more) the battery voltage • A resistor limits the output current under short-circuit conditions to A-H/10 charging rate

  22. Electronic constant current charger based on three-terminal voltage regulator

  23. Constant voltage (CV)

  24. 19-12 Other Batteries 19-12-1 Lead-acid batteries • 優點：reliable and easily available • 缺點：very heavy and dangerous • 用途：high-power portable applications (automobile battery is often preferred) • 保養： • Water level in each of the cells must be checked periodically (weekly) • Clean the cap or replace it • Warning：Lead-acid batteries produce hydrogen as a normal byproduct

  25. 19-12-2 Carbon-zinc and alkaline dry cells • 一般的用途(閃光燈、收音機、……) • 缺點： • 不可充電，用完就丟 • 端電壓在使用時下降很快

  26. 19-12-3 Mercury dry cells • 優點：在電池壽命結束前，端電壓幾乎維持定值 • 用途：儀器校正用 • 保養：如同NiCd batteries、carbon-zinc, alkaline，水銀電池在不使用的時候最好放在冷的環境中(ex.冰箱)，增加電池存放時間

  27. 19-12-4 Gel-cell batteries

  28. 19-12-5 Lithium cells • 優點：壽命長 • 用途：電腦、手錶、數位儲存記憶單元 • Warning： • 注意過充或過熱的問題 • 不可攜帶到大氣壓力較小之處，如國際航線班機

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