C) 13K, gin bd viing cam xuat hien hai vach hep vdi cudng do manh d 456nm va 461nm n i m trdn nen cua dam phat quang mau xanh lam tir
H-BO TRI THirC NGHIEM VA KET QUA 1 Cau triic cua he thu phd cai tien.
1. Cau triic cua he thu phd cai tien.
CPU ^ LPT I ^ LPT I Port B Signal In ! Spectral, : V Siignal ; GPIB interface lock-in ainj)lifier ill Chopper Signal GDM -1000 Step .Motor
Hinh 2: Sa do quang cua mdy doii sac
GDM-1000
u^ t 7 c ^- jw • 1 - .1 J ' ^- ^ I-Khe vao; 2 J - GuoTig; 4 - Chopper;
Hmh 1: Sa ao khoi cua he thu pho aa duac ? ^ /- - / , • - z^j
y ^ • 3,6 - Cach tu; / ~ Khe ra nang cap nang cap
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Sa đ khdi cua he thu phd cai tien dugc bieu dien trong Hinh 1. May dan sac GDM-1000 bao gdm hai each tu 650vach/mm, vung phd hoat đng tu 7500 - 16675 cm'' (ung vdi phd bac nhat) va tu 16675 - 28700 cm'' (umg vdi phd bac hai). Hinh 2 bieu dien sa đ quang ciia may GDM-1000. Bd phan tu ghi dugc thao ra thay vao
do sd lieu dugc luu tru \k xir ly bang may tinh ca nhan (PC). Mdt md ta budc
l,8%udc dugc lap vao \'i tri thich hgp de quay each tu chgn budc sdng. Mdt budc nhiy cua mota nay lam thay đi sd sdng la 0.0832cm' .De dieu khien md ta budc naỵ chuong trinli dieu khien se giri mdt day cac sd nhi phan bdn bit qua cdng song song (LPT) cua may tinh theo thu tu: 0001; 0011: 0010; 0110; 0100; 1100;^1000^;
1001 tuang ung vdi cac \\ tri budc 1 ^ 2 -> 3 ^ 4 ->5 -^6 -^1 ->8 [3]. Cac tin
hieu nay chi la cac muc logic TTL nen can phai cd mdt bd dem trudc khi dua d^n mo ta budc.
Nhan quang dien M12FC (head-on) cua may ghi phd GDM-1000 nhay \di viing buac sdng 400-500nm (hinh.3a). Vdi \'ung budc sdng nay cac phep do phd huynh quano cung nhu Raman bi han che rat nhieụ Nham md rdng \-ung dap ung budc sdn^rnhan quang dien R-928 (side-on) ciia Hamamatsu da dugc lua chgn tha\ th6 chôM12FC (head-on). Dac trung dap irng phd cua R-928 dugc cho tren hinh 4b. Nhan quang R-928 su dung photocathode phan xa lam bang \at lieu multialkalin. bo nhan dien tir cd ciu true Idng trdn. dap irng phd rong (185-190nm>. do nha\-
cathode cao (74mA/W tai 400nm) ciing vdi cac dac trung tri va trdi theo thdi gian rat thap. Bg phan chia the va ngudn cao ap cung cap cho nhan quang R-928 dugc cau tao trong mdt bg de cam hieu C6270 - Hamamatsụ Dd cim C6270 diing neudn nudi 15 Vdc va tao ra the cao ap cd the lap trinh dugc tir 0 đn 1250 Vdc. Thd cao ap d ldi ra dugc lap trinh bang viec thay đi dien ap ldi vao didu khidn tir 0 đn 5 Vdc, dac trung lap trinh nay ciia C6270 cd do tuydn tinh rit cao, thdi gian dap img nhanh va đ eon the nhd. I . O K I O ' ẹoxio" 6.0x10"' 4.0K10'' 2.0K10"' 0 . 0 \ \ V.^_ IS il IS 400 450 500 550 600 650 700
bJdc s6ng(nm) • I D : ICO j c c 40O soc- eca
' * V A V = L E N 0 ~ H T-.r
&X. i o & 1 0 3 :
Hinh 3: Do nhay pho cua nhdn quang MI2FC (a) va nhdn quang R-928 (b)
Tin hieu phd tir nhan quang dugc dua den bd khuyech dai lock-in SR830. Sa đ khdi cua SR830 dugc cho tren hinh 4. SR830 la mot bd khuyech dai lock-in sd sir dung bd xu ly tin hieu sd Motorola 24-bit DSP56001 va vi xir ly 80C186.
Tin hieu ldi vao sau khi dugc tien khuyech dai dua den bd ADC chuyen thanh sd. SR830 cd the tu phat ra tin hieu Reference (ref ndi) hoac dimg Referece ngoai fref ngoai - thudng den tir chopper) rdi diing mdt vdng bam pha (PLL) de tao ra tin hieu sin thuan nhat, tiep đ dua vao bd tao ham sin. Sau đ ca hai tin hieu sd nay dugc dua đn bg DSP tai day cac thuat toan lock-in dugc thi hanh mot each hoan toan ly tudng. Trong DSP cung chira cac bd Igc sd giiip thi hanh chirc nang Igc tan ma khdng cin cd cac mach Igc RC nhd vay cd the loai bd meo dung cụ Ket qua sd cua phep nhan lock-in dugc liy ra nhd giao difn RS232 hoac giao dien GPIB, ket qua
nav cung dugc dua tai bd bidn đi DAC dh cd the lay ra a ldi ra tuang tu (Analog
Output). Toan bd hoat dgng cua lock-in SR830 dugc dieu khien thdng qua cac chuin RS232 hoac GPIB (IEEE-488).
Viec aiao tidp giiia may tinh va SR830 sir dung cac ky tu ASCIỊ Mdi lenh tdi SR830 bao R6m 4 k7 tu ggi nhd. cac đi sd can thiet, va mot dau ket thiie lenh. Dua
tren nauyen^tic nay chiing tdi da \\k mot phan mdm bang ngdn ngir Basic chay iren
PC dfdidu khi^n va thu thap xir ly so lieu tir bd lock-in SR830. Sd lieu nhan tii-
lock-in dugc luu tru \k bilu dien true tilp thanh đ thi hien thi tren man hinh trong
Low Noise Differential Amp \'oItage -^ B Current I Reference in 50/60 HZ Notch Filter 00120 HZ Notch Filter Gain DC Gain Offset Expand YOut XOut Discriminator Sine Out TTL Out Discriminator
Hinh 4: Sa do khoi cua khuyech dai lock-in SR830
r r j [ ^ i
Hinh 5: Giao dien cua chuarig trinh do pho (adsbygoogle = window.adsbygoogle || []).push({});