May do kim loai dung nguyen ly xung cam ung.
Phgm Qudc Trim", Lini Tien Manh'', Trien Qudc Lgc'', Nguyen Ddng Lam", Phgm Vdn Thdnh"
a) Tnrovg Dgi hgc KHTN, DHQGHN h) Vien nghien ciru KHKT bdo hd lao dgng
Tom tdt:
'^Trong bdi bdo ndy, cdc tdc gid gidi thi^u mgt thiet bi phdt hien kim logi tir che tgo sir dung hieu I'rng xung cam irng. Ddu dd Id cudn ddy nhieu vdng ddng tdm dgng dia. Tin hieu thu dugc tir ddu dd Id .sudt dien ddng cdm irng tgi sirdn xudng ciia xung kich thich. Tin hieu ndy cd do tre khdc nhau khi cd vd khdng cd kim logi trong vung nhay cdm cua ddu dd. Nhd ky thuat xir ly tin hieu kieu boxcar, thiet bi se chi thi phdt hien kim logi. Thiet bi dd hogt ddng dn dinh, de Idp rap, gid thdnh thdp vd dang hudng tdi irng dung trong cdc xuang gia cdng che bien gd.
Abstract:
In this article, the authors introduce a home made detecting metal device using induction pulse effect. The detector is in flat coil shape. At the down slope of excited pulse, the inductive current appears. The delay time of these signals is different from two cases: in existence and not existence of metal.
With the boxcar technique is used for signal treatment, the existence of metal in the sensitive area of the detector will be discovered. The operation of device is rather stable. This device can be manufactured easily with low price. It can be applied to wood processing factory.
LMdddu
Trong cupn day cd N vdng, sudt dien ddng cam ung <f dugc tfnh theo bieu thirc sau:
4 =-Nd(D/dt (1)
O = LI (2) trong dd 0 Id tu thdng di qua tiet dien cudn day,
L la he sd tu cdm, phu thupc vao cdu tao hinh hpc, kfch thudc, vat lieu trong cupn day, I la cudng dp ddng dien trong cudn day.
Thay (2) vao (1) ta dugc:
I = -NdO/dt = -Nd(LI)/dt = -NL dl/dt (3)
Cdng thiic (3) chiing td trong cudn day xudt hien sudt dien ddng tu cdm khi:
Ddng dien trong cudn ddy bien thien - He sd tu cdm L ciia cudn day thay ddi
Mdy dd kim loai theo nguyen ly xung cdm ling do chiing tdi thiet ke che tao dua tren hieu ling CO bdn ndi tren. Chiic ndng ciia thiet bj la phdt hien cac vat kim loai cd tir tfnh nhu dinh, mdnh bom dan an chiira trong gd nhdm ddm bdo an toan cho ngudi va may mdc trong qua trinh gia cdng che bien.
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II. Thiet Ice che tao
May dd kim loai dupe thi6l ke nhu so dd khdi tren hinh 1. Cd ba khoi thuc hien cac nhi?ni vu chii chdt, dd la:
Khdi dau dd kim loai (sensor)
Khdi xii' ly tin hieu cam ung (khdi so 5)
Khdi Idy mau tin hieu theo ky thual Boxcar (khdi sd 7)
Dau dd kim loai la eupn day dang dia cd dudng kfnh D = 150 mm, so vdng N = 100.
D6 tao su bien thien ddng dien trong cupn day, chuoi xung vudng tudn hoan tdn sd 27 Hz dupe sir dung trong mach kfch phat (khdi 3).
1.Kh6lt?io xung d6ng bd
2.KhAldlAu chlnh d^
ring «ung
3 Khoi Kich p h i t l h i m d 6
4 Kh6l t?o
xung chuln S B^
to (inh
E. Khoi tfo xung lAy miu
KhAl hiin thi
r.SwHch
^ lAy mlu B KhAi KO lin h l ^
9 B4 chia tin 74LS78
Hinh 1. So do khoi may do kim loai trong go
Tai Idi ra ciia ddu dd, tfn hieu cdm ung xudt hien vdo thdi diem sudn xudng cua xung kfch thfch. Nhiem vu chii yeu cua Bd so sdnh (khdi 5) Id cdt bd nhirng phdn khdng can thiet trong dang tfn hieu cdm ling, chi giu: lai phan thdng tin lien quan den ddi tugng dd tim. Cu the nhu sau: (i) tmdng hgp khdng cd ddi tugng kim loai gdn ddu do, tfn hieu cdm ung cd dang doc xudng manh Oi) tmdng hop cd ddi tugng kim loai gdn ddu do, tfn hieu cdm img thodi hem tuy theo khodng cdch vd khdi lugng kim loai.
Nguyen nhdn cua hien tugng Id do su thay ddi he sd tu cdm cua cudn day ddu dd khi khdng cd vd khi cd mat ciia vdt lieu. Ndi cdch khdc, dp tir thdm cua mdi tmdng trong hai tmdng hgp la khdc nhau. Ddy cung chfnh la nguyen ly lam vi?c cua ddu dd (sensor). Hinh 2 minh hpa nguyen ly boat ddng ciia ddu dd, tfn hieu dugc th§ hien sau Bp so sdnh (khdi 5) tren hinh 1 [3].
Hinh 2. Tin hieu cam irng tren dau do trong hai trirdng hpp:
a) khdng cd kim logi (duang lien net) b) cd kim logi gdn ddu dd
(duang dut net)
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uuii iicii su knac biet ve dp tre ndi tren, khdi lay mdu tfn hieu dupe thidt ke nhdm muc dfch nhdn biet vd dua ra chi thj su tdn tai kim loai trong vung cdn phdt hien [4]. Nguyen ly cua khdi lay mdu tfn hieu (khdi 7 hinh 1) dupe tnnh bdy tren hinh 3.
(a)
(b)
(c)
(d)
A. , X
Hinh 3. Nguyen ly ciia khoi lay mau tin hieu a) Tin hieu cdm irng khi khdng cd kim logi b) Tin hieu cdm irng khi cd kim logi
c) Xung Idy mdu
d) Lay mdu tin hieu cdm img
Nhu vay, sau khdi Idy mau tin hieu, ta se nhan dugc (i) miic dien dp VI n§u khdng cd kim loai gdn ddu dd (ii) miic dien dp V2 ( vdi V2>VI) neu cd kim loai gdn ddu dd. Tren co sd dd, sau khdi 8 ta se nhan dugc mgt xung dien dp bdo hieu sir tdn tai cua kim loai trong viing can phat hien. Do tan sd cua xung sau khdi 8 chua du thdp de dua ra chi thj, bd chia tan diing trigor 74LS76 dugc sii dung tai khdi 9. Viec chi thj dugc thiet ke theo nguyen tac:
- Khdng cd kim loai gdn dau dd: den xanh ludn sang bdo trang thai an todn.
- Cd kim loai trong vung bdo ve: den dd bat len bao hieu trang thai nguy hiem. Ddng thdi vdi chi thi den dd, cd the su dung xung bao hieu dieu khien role bdo ve.
i n . Do dac khao sat
Chiing tdi da tien hanh do dac, khdo sat tfnh nang dp nhay ciia mdy dd kim loai thdng c \u cac thf nghiem:
- Kiem tra dp nhay ciia mdy dd vdi cdc mau kim loai cd khdi lugng khdc nhau, tim kb ng each tdi da cd hieu ung.
Cu the cdc mdu dugc chpn thu nghiem la: mi=5g; m2=8g; m3=10g; m4=16g.
Khodng each tdi da cho hieu ung phdt hien tuong irng vdi cdc mdu tren la:
H|=ll,5cm; H2=12,5cm; H3=13,8cm; H4=14,6cm.
Kiem tra dp nhay ciia may dd thep tpa dp dat mau kim loai.
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Ket qud do dac cho thdy, tren tnic chfnh tam cua sensor, may dd nhay vdi cdc mdu kim loai nhdt, d cac phuong khac, dp nhay ciia may dd kem han.
Hinh 4 md la viing nhay cam eiia may dd ddi vdi mdu sdt cd khdi lugng m=16g, H'iJC lung hi dd cao so vdi mat sensor, tmc hoanh la khoanu each tfnh tii' tam sensor tfnh theo cm.
Hinh 4. Viing khong gian phat hi^n kim loai cua dau do kim loai IV. Ket luan
Cdc ket qud thuc nghiem, do dac vdi mdy dd kim loai da cho thdy cdc sd lieu hodn todn ddp img dugc cdc chi tieu, yeu cdu ky thuat ddt ra cho mpt thilt bj phdt hien kim loai trong go [1,5]. Tren thuc tk, kim loai dn chiira trong go da so Id sdt (dinh, mdnh bom). Thiet bi hoat ddng dn djnh, tin cay [4], de nhdn bdn trong diku kien Viet nam, gid thanh ha. May dd kim loai trong gd da dugc chung tdi che tao thir nghiem dudi hai dang: mdy gdn cd dinh va may xdch tay, hudng tdi muc tieu gidm thieu tai nan trong cdc xudng gia cdng che bi6n go.
Tai lieu tham khao
[1] TCVN 2293:1978, Gia cdng go -Yeu cdu chung vk an todn.
[2] TCVN 4722:1989, Thikl bj gia cdng go -Yeu cdu ky thuat chung.
[3] M A Pai, D P Sen Gupta, K R Padiyar, Small signal analysis of power systems, Narosa Publishing House, New Delhi, (2007 Edition).
[4] T.S. Rathore, Digital measurement techniques, Alpha Science Intemational Ltd., Pangboume England, (2003).
' [3] Safety and Health at Work, ILO-CIS Bulletin No5, vol.2, (1998).
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