Dab tsi yog qhov cuam tshuam ntawm Electromagnetic cuam tshuam ntawm Thermocouple Accuracy?

Electromagnetic cuam tshuam (EMI) yog ib qho ntawm feem ntau thiab ntxhov siab qhov chaw ntawm thermocouple yuam kev nyob rau hauv kub khiav tshuab. Thermocouple's low-theem millivolt teeb liab yog qhov ua rau muaj kev cuam tshuam loj heev los ntawm AC fais fab kab, lub cev muaj zog, sib txawv - zaus tsav, thiab txawm tias cov khoom siv vuam nyob ze. Cov teebmeem tseem ceeb ntawm EMI yog suab nrov, offset, thiab tsis ruaj khov. Lub suab nrov tshwm sim raws li qhov sib txawv ntawm qhov ntsuas kub, feem ntau ± 1-5 degree, ua rau lub voj voog tswj 'hloov' thiab lub voj voog cua sov sai. Offset tshwm sim thaum EMI qhia qhov tsis tu ncua DC voltage, hloov kev nyeem ntawv los ntawm ob peb degrees. Instability yog sib quas ntus, ua rau tam sim ntawd dhia nyob rau hauv qhov kub thiab txias uas ua rau lub tswb los yog ua rau tus maub los ua yuam kev. Lub hauv paus ntawm EMI feem ntau yog cov cua sov cables lawv tus kheej-lawv nqa cov tam sim no siab (txog 30 amps) ntawm 220V lossis 480V, ua kom muaj zog electromagnetic teb. Yog hais tias cov xov hlau thermocouple tau khiav mus rau qhov sib npaug ntawm cov khoom siv hluav taws xob hauv tib lub raj lossis cov tais cable, cov hlau nplaum sib nqus ua rau muaj qhov hluav taws xob hauv lub voj voog thermocouple proportional rau tus nqi hloov ntawm lub rhaub tam sim no (uas yog siab vim yog 50/60Hz AC). Qhov no induced voltage ntxiv rau lub thermocouple lub teeb liab, ua rau muaj kev ua yuam kev. Txhawm rau tiv thaiv qhov no, tswj kev sib cais yam tsawg kawg 30 cm ntawm cov kab hluav taws xob cua sov thiab cov thermocouple cables, thiab siv cov hlua tiv thaiv kev sib tw -pair cables. Cov ntaub thaiv npog yuav tsum tau grounded ntawm tus maub los kawg nkaus xwb- yog grounded ntawm ob qho kawg, ib lub voj hauv av tsim, uas kuj yog qhov yuam kev. Lwm qhov kev ua txhaum loj yog cov khoom siv - xeev relay (SSR) siv los hloov lub tshuab hluav taws xob. Kev hloov pauv sai ntawm SSR's (tshwj xeeb tshaj yog theem- hom kaum) tsim cov suab nrov hluav taws xob uas ua khub rau cov teeb liab nyob ze. Siv xoom- hla SSRs txo cov suab nrov no. Tsis tas li ntawd, yog hais tias lub thermocouple yog grounded (txuas txuas nrog sheath), thiab lub sheath yog grounded rau pwm, thaum lub maub los yog grounded mus rau lwm qhov chaw hauv av, ib lub voj hauv av, tsim kom muaj DC offset. Siv cov thermocouples ungrounded (cais tawm) los rhuav tshem lub voj no, lossis xyuas kom tus maub los muaj cov khoom siv sib cais. Txhawm rau kuaj xyuas EMI, khiav ib ntus tshiab ntawm lub thermocouple ncaj qha mus rau tus maub los, khiav deb ntawm tag nrho cov fais fab cable. Yog tias qhov kev nyeem ntawv ruaj khov, qhov kev qhia thawj zaug yog qhov teeb meem. Yog tias koj muaj lub oscilloscope portable, koj tuaj yeem soj ntsuam lub suab nrov waveform. Txhawm rau tiv thaiv EMI, qee tus tswj hwm siv cov lim dej hnyav; Txawm li cas los xij, kev lim dej kuj ua rau cov lus teb qeeb. Yog li ntawd, kev tiv thaiv los ntawm kev tsim nyog thiab kev tiv thaiv yog qhov zoo tshaj rau kev lim dej. Hauv cov nroj tsuag hluav taws xob tsis zoo, xav txog kev siv cov teeb liab cais lossis cov khoom xa tawm uas hloov cov teeb liab thermocouple mus rau 4-20mA tam sim no voj, uas yog inherently tiv thaiv EMI. Los ntawm kev nkag siab txog cov txheej txheem ntawm EMI thiab siv cov kev ntsuas tawm tsam, cov pwm tuaj yeem ua tiav cov kev nyeem ntawv huv, ruaj khov thermocouple txawm nyob rau hauv qhov chaw hnyav tshaj plaws.