s o SANH VONG PHU^ONG PHAP DUY TRI CHUAN DIEN AP
JMQTCHIEU
Phitng Thi Kieu Linh - Trdn Khde Dien Phdng Do ludng Diin - Viin Do ludng Viet Nam Tom tdt:
Thong thudng, chudn diin dp mgt chiiu dugc duy tri theo mgt nhdm cdc chudn diin dp rieng biit md gid tri ciia cluing dugc so .sdnh thudng xuyen vol nhau di xdc dinh do trdi ciia tirng chudn. Nhdm chudn diin dp mgt chiiu dugc so sdnh dinh ky vai chudn cdp cao han ben ngodi di duy tri ddn xudt chudn. Cdc kit qud cua cdc phep so sdnh vai chudn ben ngodi, cdc so lieu ve do trdi vd lan hiiu chudn cuoi ciia chudn ben ngodi cho phep ta thiit lap dugc do on dinh cua nhdm chudn vd du dodn dugc gid trf cua nd trong tuong lai vai do tin cay cao.
Bdi bdo ndy trinh bdy phuong phdp so sdnh vdng sir dung trong viec duy tri nhdm chudn diin dp mgt chiiu.
Abstract:
Traditionally, maintaining a high-performance DC Voltage reference meant using several independent voltage references that were regularly compared with each other to identify excessive drift in any one und, and routinely compared with external voltage standards to maintain traceability. The results of comparisons with higher-order external standards allowed a history to be established for the group of references so that their future performance could be predicted with a high degree of confidence from their recorded drift rate and date of last calibration.
This paper describes the intercomparison procedure which is applied to maintain a group of DC voltage standard.
L M d D A U
So sdnh vdng la phuang phdp dp dyng cho vide tfnh todn gid trj cua mdt nhdm dien dp chuin mdt chilu (pin chuin) cimg dai lugng thdng qua viec thye hidn cdc phep do vi sai timg cap vdi nhau theo ma Iran vudng trong dd gid trj trung binh Id xdc djnh. Mdt nhom chudn dien dp thudng bao gdm ft nhit 4 pin chuin, gid trj trung binh cua nhom chuin nhdn dugc tir viec so sdnh vdi chuin cip cao hom ben ngoai, tir dd cho phep ta tfnh todn dugc gid trj ciia tirng pin chuin vd ddnh gid dugc do dn djnh cua nhdm chudn.
II. PHlTONG P H A P
9 1 1
Mdt nhdm gdm n pin chuin cd gia trj trung binh biet trudc Id M, n pin chudn nay se Idn lugt dugc so sanh vdi nhau thdnh timg cap theo hai chilu thuan nguge de tim ra do chenh dien dp.
Ggi U la s i lugng cdc gid trj dien dp cdn tfnh loan; P Id s i lugng cdc phep do can thye hien; F la bae ty do; khi dd ta cd:
P = n(n-1) U = n
F = P - U = n^ - 2n
Vdi mdt nhdm gdm 4 pin chuin dien dp (n = 4) thi s i lugng cdc phep do do chenh dien dp ciia timg cdp la 12, trong dd co 6 phep do thuan vd 6 phep do nguge (the hien trong bang 1).
Ggi Ei la didn ap thir i trong nhdm chuan Ggi Ej la didn ap thu' j trong nhom chuan
yji la gia tri chenh dicn ap iziua pin chuan thu i so vdi pin chuan thir j (hang thir i cot thii ciia bang 1). Khi dd ta co:
y,j= E|-E|+B+e,i (pV) (cdng thiic 1) ( i = l , 2 , . . . n , j = l , 2 n;i^j)
B la sire didn ddng nhiet va e la gia trj didn ap du (sai sd) trong mach do.
Tdng binh phuang didn dp du Irong mach do chia cho F dugc ggi la do lech chudn thue nghiem.
Khi Ihuc hidn cac phep do ta cd cac gid trj yij, lir cac gid tri do nay la cd the tfnh dugcB vavavi E theo cdng thirc dudi day:
E, =M+ — Y,(y„ -yJ (k=l,2,...n) (cdng thiic 2) 2n ;=,
B =
n
•Z-v
(cdng Ihuc 3)n(n-l)f:^j"
Tir cac gid trj Ek va B tim dugc ta cd the sii dung cdng Ihuc 1 dk tfnh ra Cjj.
Bang 1. So sanh vdng cua 4 pin chuan di^n ap
1 2 3 4
1
—
R R R
2 F
—
R R
3 F F
—
R 4 F F F
—
Vdi F: phep do thuan R: Phep do nguge Khi dd, do lech chudn thye nghiem:
2
n - 2/1 (cdng thirc 4)
Phuomg sai thye nghiem cua E vd B dugc tfnh theo cdng thirc nhu sau:
s.e-(E) =—^(n-l)s-(cdng thiire 5)
2/7"
s.e-(B) = I
(cdng thirc 6) n(n-l)
(s.e: standard error)
Vdi nhdm pin chudn dien dp cd n =4 nhu tren ta cd Ihl tfnh dugc:
E i = M + ( i / 8 ) ( y 2 i yi2 + y3i yi.-? + y4i y u ) E2=M-l-(l/8)(yi2 - y2i + y32 - y2.3 + y42 - y24) E3=M-f-(l/8)(yi3 - y3, + y23 - y32 -I- y43 - y,^)
B=(I/12)( yi2 + yi3 -l- y,4 + y2| -1- y23 + y24 + y.ii + y.32 + y34 + y4i + y42 + y43)
Tir cdc cdng thirc 4,5,6 ta cd:
s =(l/5)( e 12 + e"i3 + e'u -i-e"2i +e 23 +e 24 +e 31 +e 32 +e 34 +e"4i +£"42 +e 43) s.e^(E)=(3/34).s-
s.e-(B)=(l/12).s'
Vf dy: Mdt nhdm gim 4 pin chuan dien dp mdt chilu cd gid trj dien dp trung binh la 1.01861447 V. Cac phep do theo phuang phap so sanh vong se dugc thye hien theo bdng sau (don vj la microvolt):
1 2 3 4
1
—
+27.9 +31.6 +38.9
2 -27.8
+3.8 +11.2
3 -31.5 -3.8
+7.5 4 -38.5 -11.3 -7.4
—
Sir dyng cdc cdng thu:c 2 vd 3 se cho ta cdc gid trj dien dp can tfnh nhu sau:
E,=1.01863900V E2=1.01861127 V E3=1.01860750V E4=1.01860012 V
s=0.158pV s.e(E)=0.048 pV s.e(B)=0.046 pV
HI. CHUAN DIEN AP MQT CHIEU TAI V I £ N DO LU^OfNG VIET NAM
Chudn dien dp mdt chidu ciia Vien Do ludng Vi?t nam dugc duy tri theo mgt nhdm gdm 4 pin chudn didn tir kilu Fluke 7000 cd gia trj danh dinh la 10 V vd 1.018 V Nguyen ly cdu tao dua trdn cdc diot zener bii nhidt cd do on dinh cao theo thdi gian vd khdng chju nhieu anh hudng cua yeu td nhiet do. Gid trj trung binh ciia nhdm chuan dugc duy tri vd ddn xuat din chuan dau dien ap mot chieu Josephson ciia Vien Do ludng Han Quoc thdng qua chuan sao truyen Fluke 7328 (Transfer standard). Chuan didn dp mdt chieu fluke 732B cd do ti-di hang nam la 1 ppm cd gia trj danh dinh la 10 V va 1.018V mgt chieu. Tir ket qua hieu chuan ciia chuan Fluke 732B tai han quoc, ti:r do trdi tinh todn hang nam vd phuang phap so sdnh vong cd thi thidt lap dugc dg on djnh ciia nhdm chudn didn dp 1 OV mgt chidu. Nhdm chudn dien ap mgt chieu Fluke 7000 Serial dugc duy tri tir ndm 2005 den nay cd dg trdi tinh todn trung binh mdt nam cd 3 ppm dugc the hien theo hinhl dudi ddy:
C h u a n dign a p m g t c h i e u F l u k e 7 0 0 0 — Standard No.1
^~- Standard No.2 Starxiard No.3 -•—Average Value
E a a
nim
Hinh 1, D9 troi cua nhom chuan dien ap m^t chieu Fluke 7000
9 9 r
Cdc yeu td dnh hudng den do khdng ddm bdo do ciia phep do:
Do khdng ddm bdo do cua chudn sao yuyin Fluke 732B dugc liy yong gidy chimg nhdn hieu chudn tai Vien Do ludng Hdn Quic KRISS;
Do ydi cua chuin Flule 732B dya yen ljch sir duy tri chuin hdng nam;
Nhiet do: do chenh dien dp giira noi hieu chuin Fluke 732B (Vien do ludng Han qu6c- xem yong gidy chimg nhdn hieu chuin phin dilu kien mdi tiirdng) vd nhiet do phong thi nghidm (Phdng Do ludng Didn VMI)
Hmh 2. Nhom chuan dien ap mot chicu tai Vien Do lucmg Viet Nam rV. DANH GIA
Duy tri gia trj trung binh cua nhdm chuan dien dp cd nhieu uu diem hom so vdi viec duy tri mdt chudn don Id, day Id giam dugc nhidu yong phep do, gidm dugc dnh hudng ciia yeu Id nhiet do, dy doan vd do trdi tdt hom ddn den kdt qud do khdng dam bdo nhd hon. Ngdy nay hieu ung Joshepson la chuin ddu dien dp 10 V mdt chieu, my nhien de duy tri hifu ring thi chi phi rit ddt dd, vi vay vide duy tri mdt nhdm pin chudn dien tir ngdy cang phd bien d cac nudc dang phdt tridn. Phuang phdp so sdnh vdng dugc sir dung rdng rai de duy tri nhdm chuan didn dp mdt chidu d nhidu Vien do ludng Quic gia md chua cd khd ndng yang bj chudn ddu dien dp Josephson. Nhdm chudn dien dp mdt chilu Fluke 7000 Serial dugc duy tri vd bdo qudn bdi Phdng Do ludng Didn-VMI la he thing chuan didn dp mdt chilu cao nhdt cua Viet Nam. Viec chiing tdi dp dung phuang phdp ndy kit hgp vdi dir lieu chuan sao truyen sir dung trong qua trinh duy tri chudn cho phep chung tdi ddnh gid dugc do in djnh, dy doan dugc gid yj thye cua nhdm chuan trong tuong lai vdi do tin cay cao.
T A I LIEU THAM KHAO
[I] "VS4 Instruction Manual", Statronics Power Supplies, 1987, myc 8 yang-39 [2] "734A DC Reference Standard", Fluke Mfg Co., Ltd ,1990
[3] "Phylosophy in Practice- Calibration ", Fluke Mfg Co., Ltd
[4] "Fluke 7000 Volt Maintenance System-Users Manual", Fluke Copovation,2000
