影(ying)響電阻或電阻率測試的主要(yao)因素

  a．環境溫濕度： 一般材料的電阻值隨環境溫濕度的升高而減小。相對而言，表面電阻(率)對環境濕度比較敏感，而體電阻(率)則對溫度較為敏感。濕度增加，表面泄漏增大，體電導電流也會增加。溫度升高，載流子的運動速率加快，介質材料的吸收電流和電導電流會相應增加，據有關資料報道，一般介質在70C時的電阻值僅有20C時的10％。因此，測量材料的電阻時，必須指明試樣與環境達到平衡的溫濕度。

  b．測(ce)試(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(電(dian)(dian)(dian)(dian)(dian)(dian)(dian)場強(qiang)度):  介質(zhi)材料(liao)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(率)值(zhi)(zhi)一般(ban)不(bu)能(neng)在(zai)很(hen)寬的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓范圍內(nei)(nei)保(bao)(bao)持不(bu)變(bian)(bian)(bian)，即歐姆定律對(dui)此并不(bu)適用。常溫條(tiao)件下(xia)，在(zai)較低(di)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓范圍內(nei)(nei)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)導(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)隨外加(jia)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)增加(jia)而線性增加(jia)，材料(liao)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)值(zhi)(zhi)保(bao)(bao)持不(bu)變(bian)(bian)(bian)。超過(guo)一定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓后，由于離子化運動加(jia)劇，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)導(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)增加(jia)遠(yuan)比測(ce)試(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓增加(jia)的(de)(de)快，材料(liao)呈現的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)值(zhi)(zhi)迅速降低(di)。由此可(ke)見，外加(jia)測(ce)試(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓越高，材料(liao)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)值(zhi)(zhi)越低(di)，以致在(zai)不(bu)同(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓下(xia)測(ce)試(shi)(shi)(shi)得(de)(de)到的(de)(de)材料(liao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)值(zhi)(zhi)可(ke)能(neng)有較大的(de)(de)差(cha)別。值(zhi)(zhi)得(de)(de)注意的(de)(de)是，導(dao)致材料(liao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)值(zhi)(zhi)變(bian)(bian)(bian)化的(de)(de)決定因(yin)素是測(ce)試(shi)(shi)(shi)時(shi)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)場強(qiang)度，而不(bu)是測(ce)試(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓。對(dui)相同(tong)的(de)(de)測(ce)試(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，若測(ce)試(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)之間的(de)(de)距離不(bu)同(tong)，對(dui)材料(liao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)率的(de)(de)測(ce)試(shi)(shi)(shi)結果也將不(bu)同(tong)，正負電(dian)(dian)(dian)(dian)(dian)(dian)(dian)極(ji)之間的(de)(de)距離越小，測(ce)試(shi)(shi)(shi)值(zhi)(zhi)也越小。

  c．測(ce)(ce)(ce)試(shi)(shi)時(shi)(shi)間(jian):  用一(yi)(yi)(yi)定的直流(liu)電(dian)(dian)壓對被測(ce)(ce)(ce)材(cai)料加壓時(shi)(shi)，被測(ce)(ce)(ce)材(cai)料上的電(dian)(dian)流(liu)不是(shi)(shi)(shi)瞬時(shi)(shi)達(da)到(dao)穩定值(zhi)(zhi)的，而是(shi)(shi)(shi)有(you)一(yi)(yi)(yi)衰(shuai)減(jian)過程(cheng)。在加壓的同時(shi)(shi)，流(liu)過較(jiao)大的充電(dian)(dian)電(dian)(dian)流(liu)，接著是(shi)(shi)(shi)比較(jiao)長(chang)時(shi)(shi)間(jian)緩慢減(jian)小的吸(xi)收電(dian)(dian)流(liu)，最后達(da)到(dao)比較(jiao)平(ping)穩的電(dian)(dian)導電(dian)(dian)流(liu)。被測(ce)(ce)(ce)電(dian)(dian)阻值(zhi)(zhi)越(yue)高，達(da)到(dao)平(ping)衡的時(shi)(shi)間(jian)則(ze)越(yue)長(chang)。因此(ci)，測(ce)(ce)(ce)量(liang)時(shi)(shi)為了正(zheng)確(que)讀取(qu)(qu)被測(ce)(ce)(ce)電(dian)(dian)阻值(zhi)(zhi)，應在穩定后讀取(qu)(qu)數值(zhi)(zhi)或(huo)取(qu)(qu)加壓1分鐘后的讀數值(zhi)(zhi)。另(ling)外(wai)，高絕(jue)緣材(cai)料的電(dian)(dian)阻值(zhi)(zhi)還(huan)與其(qi)帶電(dian)(dian)的歷史有(you)關。為準確(que)評(ping)價材(cai)料的靜電(dian)(dian)性能，在對材(cai)料進(jin)(jin)行電(dian)(dian)阻(率)測(ce)(ce)(ce)試(shi)(shi)時(shi)(shi)，應首先(xian)對其(qi)進(jin)(jin)行消(xiao)電(dian)(dian)處理(li)，并靜置一(yi)(yi)(yi)定的時(shi)(shi)間(jian)，靜置時(shi)(shi)間(jian)可取(qu)(qu)5分鐘，然后，再按(an)測(ce)(ce)(ce)量(liang)程(cheng)序測(ce)(ce)(ce)試(shi)(shi)。一(yi)(yi)(yi)般而言(yan)，對一(yi)(yi)(yi)種材(cai)料的測(ce)(ce)(ce)試(shi)(shi)，至少應隨(sui)機(ji)抽取(qu)(qu)3～5個試(shi)(shi)樣進(jin)(jin)行測(ce)(ce)(ce)試(shi)(shi)，以其(qi)平(ping)均值(zhi)(zhi)作為測(ce)(ce)(ce)試(shi)(shi)結果。

  d．測試(shi)設備的(de)(de)(de)泄(xie)漏(lou)(lou)：在(zai)測試(shi)中(zhong)，線(xian)(xian)路中(zhong)絕緣電(dian)(dian)阻不高的(de)(de)(de)連線(xian)(xian)，往往會不適當地與被測試(shi)樣、取樣電(dian)(dian)阻等并聯(lian)，對(dui)測量(liang)結(jie)果(guo)可能帶來較大的(de)(de)(de)影(ying)(ying)響。為(wei)(wei)此：為(wei)(wei)減(jian)小測量(liang)誤差，應(ying)采(cai)用(yong)保護(hu)技(ji)術，在(zai)漏(lou)(lou)電(dian)(dian)流(liu)大的(de)(de)(de)線(xian)(xian)路上安裝(zhuang)保護(hu)導(dao)體，以基本消除雜散電(dian)(dian)流(liu)對(dui)測試(shi)結(jie)果(guo)的(de)(de)(de)影(ying)(ying)響；高電(dian)(dian)壓線(xian)(xian)由于表(biao)面(mian)電(dian)(dian)離，對(dui)地有一定泄(xie)漏(lou)(lou)，所(suo)以盡(jin)量(liang)采(cai)用(yong)高絕緣、大線(xian)(xian)徑的(de)(de)(de)高壓導(dao)線(xian)(xian)作為(wei)(wei)高壓輸出線(xian)(xian)并盡(jin)量(liang)縮(suo)短連線(xian)(xian)，減(jian)少jian端(duan)，杜絕(jue)電(dian)暈放電(dian)；采用聚乙烯、聚四氟乙烯等絕(jue)緣材(cai)料制作測(ce)(ce)試臺和支(zhi)撐體(ti)，以避免由于該類(lei)原(yuan)因導致測(ce)(ce)試值偏低。

  e．外(wai)界(jie)干(gan)擾：高絕緣材料(liao)加(jia)上(shang)直流(liu)電壓后，通過試(shi)(shi)樣的(de)(de)電流(liu)是很微小(xiao)的(de)(de)，極易受到(dao)外(wai)界(jie)干(gan)擾的(de)(de)影響(xiang)，造成較(jiao)大的(de)(de)測(ce)試(shi)(shi)誤(wu)差(cha)。熱(re)電勢(shi)、接觸(chu)(chu)電勢(shi)一般很小(xiao)，可(ke)以忽(hu)略(lve)；電解電勢(shi)主要(yao)是潮濕試(shi)(shi)樣與(yu)不同金屬接觸(chu)(chu)產生(sheng)的(de)(de)，大約只有20mV，況且在靜電測(ce)試(shi)(shi)中均要(yao)求(qiu)相對濕度(du)較(jiao)低，在干(gan)燥環境中測(ce)試(shi)(shi)時，可(ke)以消(xiao)除(chu)電解電勢(shi)。因此，外(wai)界(jie)干(gan)擾主要(yao)是雜(za)散電流(liu)的(de)(de)耦合(he)或靜電感(gan)應產生(sheng)的(de)(de)電勢(shi)。在測(ce)試(shi)(shi)電流(liu)小(xiao)于10-10A或測(ce)量電阻超過1011歐姆(mu)時；被(bei)測(ce)試(shi)(shi)樣、測(ce)試(shi)(shi)電極和測(ce)試(shi)(shi)系統(tong)均應采取嚴格的(de)(de)屏蔽(bi)措(cuo)施，消(xiao)除(chu)外(wai)界(jie)干(gan)擾帶來的(de)(de)影響(xiang)。