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7/28/2019 Dieu Khien Nhiet Do
1/3
IU KHIN NHIT
1. Mc ch ca th nghim- Kho st c tnh h thng nhng ch cng sut in trkhc nhau tm
cc thng sc trng ca chu k vng lp: khuych i tnh, hng s thi gian, thi
gian tr.
- Xc nh cc thng siu chnh ng vi cc iu kin vn hnh.
- ng dng cc thng s va tm c cho ch vn hnh: kho st s nh
hng im ci t, ti u ha cc thng sci t.
2. C sl thuyt2.1. o nhit u d nhit c s dng trong m hnh th nghim ny l loi u d in
trkim loi s dng Platium lm cht cm bin.
Nguyn l o:
in trca cc kim loi ph thuc vo nhit . Stng in trt l vi nhit
xc nh h s nhit dng (positive temperature coefficient CTP). Trong thc t,
ch to mt u d tt, phi s dng vt liu c h s nhit cao, ng biu din s
ph thuc in trvo nhit l ng thng. Chng ta cng c th chn mt vt liu
m c th chu c nhit cao v loi c in trchun ph hp.
Platin l mt vt liu ph bin c s dng lm cht cm bin trong u d in
tro nhit trong cng nghip vi u im l bn ha hc cao, diu khin, tinh
khit rt cao v c h s nhit in trln.
Nhit c o gin tip thng qua vic o in trca phn t cm bin Pt.
Mi lin h gia nhit v in trth hin phng trnh sau:
RtR0t =
R0.t
7/28/2019 Dieu Khien Nhiet Do
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Trong : t: l h s nhit in trnhit t ( nhy nhit ca in
tr)
R0: in trti 00C
Rt: in trti t0C
2.2. Kho st h thng gia nhitNguyn l gia nhit ca bung nh sau: mt dng in qua mt ai gia nhit mica
lm kch thch s tng nhit bn trong vng ai. Vng ai c kt ni vi biu
khin cng sut in xoay chiu m c iu khin bi biu khin dng in 4 20
mA. Bny cho php iu khin vic gia nhit vi in p thp (24V AC), c binp t ngun in p cao hn (220V 50Hz).
3. Cch tin hnh th nghim3.1. Th nghim 1: Xc nh cc thng sc trng ca h thng
- Bt my.- Chn chManual.- Nhp gi trOP=0%, i h thng n nh (gi trPV khng i theo thi gian hay
ng biu din PV l ng nm ngang), ghi nhn gi tr nhit n nh ca h
thng.
- Tip tc nhp OP=10%, i h thng n nh, ghi nhn gi tr nhit n nh cah thng.
- Tng t ta lp li qu trnh ny vi cc gi tr khc ca OP (mi ln tng 10%)cho n khi OP=100%.
3.2. Th nghim 2: Xc nh cc thng s iu khin theo phng phpBroida
- Chn chManual.- Nhp gi trOP=40%, i h thng n nh, ghi nhn gi tr nhit T1.
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- Tip tc nhp gi tr OP=50%, ghi nhn cc gi tr nhit sau mi 30 giy chon khi h thng n nh.
3.3. Th nghim 3: Kim chng khnng iu khin ca h thng sau khithay i thit lp
- Bt cng tc Ventilation sang v tr s1 gim nhit ca h thng xungkhong 40 0C sau chuyn li v tr Auto.
- Ci t cc thng s PB, Ti v Td va tm c phn trc.- Chnh biu khin ch Auto.- t gi tr Setpoint l 90 0C.- Ghi nhn li cc gi tr nhit theo thi gian cho n khi t n nh.4. Kt qu, th v nhn xt