Ddng hd do dien da nang hien so DT-830B (Hinh 12.4) la dung eu do dien hien dai, gdm 2000 diem do cd the hien thi bang 4 chir sd tir 0000 den 1999 nhd cac tinh the long (LCD). 6 mat sau, ben trong ddng hd cd mdt pin 9 V cdp dien cho ddng hd hoat ddng va mdt cau chi bao ve 0,2 A.
Loai ddng hd nay cd nhieu thang do ung vdi cac ehu'c nang khac nhau nhu : do dien ap mdt ehidu (DCV), do dien dp xoay ehidu (ACV), do cudng do ddng dien mdt chieu (DCA), do dien trd {Q.),...
2. Nhiirng diem can chu y thiic hien
a) Khi su dung ddng hd DT-830B, ta van niim xoay eua nd den vi tri tuong ung vdi ehiic nang va thang do can chgn. Sau dd ndi edc cue eiia ddng hd vao mach dien. Gat niim bat - tdt (ON - OFF) sang vi tri "ON"
de cac chU sd hidn thi tren man hinh eiia nd.
b) Ne'u chua biet rd gid tri gidi han ciia dai lugng cdn do, ta phdi chgn thang do cd gid tri Idn nhat phu hgp vdi chiie nang da chgn.
DT.830B "fi "- mm. mmm +iicAT.n"
Hinh 12.4
L*J Tai sao khdng dugc phep dung nham thang do cudng dp ddng dien ciia ddng ho do dien da nang hien sd de do hieu dien the trong mach dien ?
c) Khdng do eudng do ddng dien va hieu dien the vugt qud gidi han thang do da chgn.
d) Khdng ehuyen ddi chiic nang thang do eiia ddng hd khi dang cd ddng dien chay qua nd.
e) Khdng diing nhdm thang do eudng do ddng dien de do hieu dien the. B 3
f) Khi thue hien xong edc phep do, phdi gat niim bat - tat ciia ddng hd ve vi tri "OFF" dd tat dien trong ddng hd.
g) Phai thay pin 9 V ben trong ddng hd khi d gdc tren ben trai man hinh ctia nd hien thi ki hieu |+ - | . h) Phai thdo pin 9 V nay ra khdi ddng hd neu trong thdi gian ddi (khoang vai thdng) khdng sir dimg no.
V - TIEN H A N H T H I N G H I E M
B E Trong mach dien Hinh 12,3, ne'u de bien trd R hd mach, thi so chi cua vdn ke V se bang bao nhieu ? Sd chi nay cd dung bang gia tri sua't dien ddng f ctia pin dien hoa mac trong mach dien khdng ?
1. Mac pin dien hod ^ vdo mach dien Hinh 12.3, trong dd chgn dien trd RQ~20D. de eudng do ddng dien chay qua pin dien hod khdng vugt qud 100 mA va ehii y dat diing :
- Khoa K avi tri ngdt dien (OFF) ; - Bien trd Ravi tri 100 Q ;
- Miliampe ke hien sd A d vi tri DCA 200m, circ duong (+) la Id cdm "VQmA", cue am (-) la Id edm
"COM" ;
- Vdn ke hien sd V a vi tri DCV 20, cue (+) la Id cdm "VQmA", cue (-) la Id cdm "COM".
2. Gat niim bat - tdt eua miliampe ke A va ciia vdn ke V sang vi tri "ON". Ddng khoa K. Ghi gia tri dn dinh cua cudng do ddng dien / tren miliampe ke'A va ctia hieu dien the' U tren vdn keV vao Bang thuc hanh 12.1. H i
6 6 5 - V A T L I 1 i . ( C ) - B
3. Thuc hien lai ddng tde (2) neu tren ling vdi mdi gid tri dien trd eiia bien trd R, bdng cdch van niirn xoay cua nd sang vi tri tiep sau de giam ddn dien trd eiia bien trd R til 100 i^ xud'ng tdi 30 Q, mdi Idn giam 10 Q.
4. Diing vdn ke hien sd dat d vi trf thang do DCV 2000m, Idn lugt mdc song song vdi dien trd R^ va R^
trong maeh dien Hinh 12.2 de do hieu dien the U' d hai ddu mdi dien trd ting vdi cudng do ddng dien / chay qua edc dien trd. Tu dd suy ra gid tri ciia RQ va 7?^ theo cdng thirc : R = — Ghi cdc gid tri U' ciia RQ va R^ vao Bang thuc hanh 12.1.
5. Xde dinh gid tri sua't dien ddng f va dien trd trong /• eua pin dien hod theo mdt trong hai phuong dn sau day :
O
Hinh 12.5
. PhUCng an thtirnhat
Can cii cac gid tri tuong ting ciia I va U trong Bang thuc hanh 12.1:
a) Ve dd thi (J = f(I) bidu didn su phu thude ciia hieu dien the JJ ciia doan mach MN chiia ngudn dien vdo eudng do ddng dien / trong doan mach (Hinh 12.5) dd nghiem lai he thiic (12.1). CE
b) Xac dinh toa do U^ va I^ ciia cdc didm tai dd dudng keo dai eua dd thi U = /(/) cdt true tung va true hoanh :
/ = 0 = U = 0
t/„
RQ+r
(12.3) (12.4) Tu (12.3) va (12.4), suy ra gid tri suat dien ddng va dien trd trong /• eiia pin dien hod.
tMi Phai ve dudng bieu dien cua dd thi U = f(I) nhu the nao de phu hgp vdi phep tinh gia tri trung binh (thong ke) ddi vdi cac gia tri I vail ghi dugc trong Bang thuc hanh 12,1 ?
/o
Hmh 12.6
Phuong an thiir hai
Cd the viet he thiie (12.2) dudi dang :
hay
voi
^ = ^{R + R^ + R^ + r)
y=^{x + b) (12.5) y= Y,x = R;b = R^ + R^^r.
Can cii cac gid tri tuong ling cua R va I trong Bang thuc hdnh 12.1 :
a) Tinh cdc gid tri tuong ling cua y va x.
b) Ve dd thi y =f{x) bieu diin gidn tiep su phu thude ciia cudng do ddng dien / trong mach kin vao dien trd cua bien trd R (Hinh 12.6) de nghiem lai dinh luat 6 m ddi vdi toan mach theo he thiic (12.2).
c) Xac dinh toa do y^ va x^ cua cae diem tai dd dudng keo dai cua dd thi y = f{x) cdt true tung va true hoanh :
y = 0=^x^ = -b (12.6) (12.7) Tii (12.6) va (12.7), suy ra gid tri sua't dien ddng va dien trd trong /• cua pin dien hod.
Ho va ten
BAO CAO THl/C HANH
Ldp .Td