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Chapter 18 Electrosurgery Generators 徐國恩 2017/5/23 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 • 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 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. • Cut • 一般不加 60 Hz filter 的 cut wave • Coagulation 18-4-1 Solid-state electrosurgery generator circuit 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 18-3 • Microscopic holes in the surgeon’s gloves • Lipuids spilled into the machine 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 使用 peak-reading meter: • Voltage divider • 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 Chapter 19 Care and Feeding of BatteryOperated Medical Equipment 19-3 Introduction Batteries are used for : • Protability • Defibrillator • Patient monitors • ECG & blood pressure • Patient safety • Cardiac output computer 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 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 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 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 Problems : • Sitting:The solution for this type of problem is a trickle charge at a rate between AH/30 and A-H/50 • Temperature effect 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 19-9 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 • 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 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 shortcircuit conditions to A-H/10 charging rate • Electronic constant current charger based on three-terminal voltage regulator • Constant voltage (CV) 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 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 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 19-12-4 Gel-cell batteries 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