Chapter 18Electrosurgery Generators

徐國恩112/04/21

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 • Coagulation

• 一般不加 60 Hz filter 的 cut wave

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

• Microscopic holes in the surgeon’s gloves

• Lipuids spilled into the machine

18-3

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 19Care and Feeding of Battery-Operated 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 A-H/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 short-

circuit conditions to A-H/10 charging rate

• Electronic constant current charger based on three-terminal voltage regulator

• Constant voltage (CV)

19-12 Other 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

19-12-1 Lead-acid batteries

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