Kev nthuav dav ntawm Capacitance-Measuring Function rau Digital Multimeters
1. Kev ntsuas hauv online ntawm capacitance
Raws li cov khoom ntawm qhov sib txawv ntawm cov khoom sib txawv, qhov ntsuas ntawm lub peev xwm tuaj yeem hloov mus rau qhov ntsuas qhov ntsuas hluav taws xob.
Lub hauv paus tseem ceeb ntawm Circuit Court CX / V txais ib qho yooj yim active RC inverse sib txawv thiab kev koom ua ke circuit. Lub Wen oscillator tsim ib lub sijhawm ruaj khov AC teeb liab Vr, uas zoo siab rau CX / V hloov pauv kom tau txais AC voltage V0 (V1) proportional rau CX. Tom qab raug lim los ntawm kev txiav txim thib ob bandpass lim kom tshem tawm cov impurities sab nraum qhov zaus, AC / DC tso zis voltage V proportional rau CX tau txais. Thaum lub teeb liab AC Vr excites lub CX / V Circuit Court, cov zis voltage ntawm inverting integrator yog
Ntawd yog, ntsuas lub peev xwm CX yog proportional rau cov zis voltage C0, yog li ua tiav CX → V hloov dua siab tshiab. Txhawm rau kom phim cov theem pib capacitance nrog 2V qib ntawm digital multimeter, qhov zaus oscillation ntawm Wen oscillator raug xaiv raws li 400Hz, qhov zoo voltage tus nqi yog 1V, R1 yog teem rau 20k Ω, thiab C1 yog teem rau 0.1 μ F. R2 txawv ntawm 2000k Ω -Ω - Ω Ω -2M Ω, sib raug rau qhov ntsuas qhov ntsuas ntawm 20 μ F-2 μ F-200nF-20nF-2nF.
2. Ntsuas me me capacitor
Qhov ntau ntawm ib tug raug peb thiab ib nrab tus lej multimeter rau ntsuas capacitance yog 2000pF txog 20 μF, thiab nws tsis muaj zog rau ntsuas me me capacitors hauv qab 1pF. Raws li txoj kev capacitance impedance thiab siv high-frequency signals, nws muaj peev xwm ntsuas me me capacitors. Daim duab ntsuas hluav taws xob tau qhia hauv daim duab 2. CX yog qhov ntsuas qhov ntsuas, thiab Rf yog cov lus tawm tswv yim ntawm qhov kawg inverting. Thaum lub input zaus ntawm sine teeb liab Vi yog f, impedance nthuav tawm ntawm CX thiab qhov nce ntawm kev ua haujlwm amplifier yog: thaum A thiab Rf tsis tu ncua, qhov zaus ntawm sine teeb liab f yog inversely proportional rau ntsuas capacitance CX. Txhawm rau ntsuas cov capacitors me, siv cov cim ntsuas siab rau kev ntsuas.
Daim duab thaiv ntawm lub hauv paus ntsiab lus Circuit Court rau kev ntsuas yog pom nyob rau hauv daim duab 2 (b). Cov txheej txheem ntsuas yog raws li hauv qab no: lub high-frequency sine teeb liab generated los ntawm high-frequency teeb liab generator yog siv rau lub ntsuas capacitor, CX yog hloov dua siab tshiab rau hauv capacitance impedance Xc, thiab ces Xc hloov dua siab tshiab rau hauv AC voltage teeb liab los ntawm C / ACV hloov dua siab tshiab, amplified los ntawm amplifier, thiab cov tso zis ntawm transformation rau theem demodulation yog rhiab heev. Lwm cov tswv yim ntawm cov theem rhiab demodulator yog lub xwmfab nthwv dej (piv txwv li demodulation teeb liab) tsim los ntawm high-frequency sine yoj los ntawm lub waveform converter, thiab ob lub input signals yog tib zaus thiab theem. Lub teeb liab demodulated yog lim los ntawm lub lim dej qis kom tau txais DC voltage proportional rau qhov ntsuas capacitance CX tus nqi, uas tom qab ntawd xa mus rau DC voltmeter rau cov khoom ncaj qha ntawm qhov ntsuas ntsuas. Lub waveform converter muaj ib tug xoom hla kev sib piv nrog inverting input, uas converts tus qauv 1MHz high-frequency sine yoj los ntawm Wen oscillator mus rau hauv tus qauv inverted square yoj. Vim lub fact tias cov zis ntawm lub theem rhiab demodulator yog ib tug pulsating DC voltage uas muaj high-frequency harmonics, ib tug π - hom lim yog siv los lim tawm harmonic Cheebtsam thiaj li yuav tau ib tug ruaj khov thiab tas li DC voltage tso zis.
Tom qab ntawd xa tus nqi nruab nrab qhov nruab nrab voltage mus rau DC voltmeter. Txhawm rau ua raws li cov peev txheej yooj yim nrog 2V ntau yam ntawm digital multimeter, qhov zaus ntawm lub teeb liab sine zaus raug xaiv raws li 1MHz (kev faib khoom yuav tsum raug txiav txim siab yog tias qhov zaus siab dhau), qhov txiaj ntsig zoo ntawm qhov hluav taws xob yog 1V, thiab cov khoom lag luam ntawm Circuit Court amplification factor thiab tawm tswv yim kuj yog Rf. Yog li, DC voltage ntau ntawm cov digital multimeter yog 200mV, sib haum rau qhov muaj peev xwm ntawm 0.2pF, thiab 200V sib raug rau qhov muaj peev xwm ntawm 200pF. Kev ntsuas ntau yog 10-4-102pF, thiab qhov kev daws teeb meem yog 10-4pF. Qhov ntsuas qhov tseeb yog
