Download - Chapter 18 Electrosurgery Generators
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