问题 问答题 论述题

使用指针式万用表时,应注意哪些事项?

答案

参考答案:

万用表测量的电量较多,量程也多,而且表的结构型式各异。往往因使用不当或疏忽大意造成测量错误或损坏事故,因此必须正确使用万用表,一般应注意以下几点:

(1)选择正确的插孔和转换开关的位置:根据测量对象,将量程开关旋至所需位置。红表笔为“+”,黑表笔为“-”,测量直流电量时,要注意极性。测量电流时,表笔与电路串联;测量电压时,表笔与电路并联。量程的选择应使指针移到满刻度的2/3附近。在被测量大小不详时,应先用高档试测,再改用合适量程。

(2)读数要正确:万用表有多条标尺,要根据被测量找到对应的标尺再读数。

(3)测量电阻时的注意事项:注意先机械调零,若改变倍率档,必须重新调零。严谨带电测量电阻。测电阻时,不能用手接触表笔的导电部分,以免影响测量结果。

(4)当量程开关置于测电阻或电流档时,切勿用来测电压,否则会立刻烧毁表头。

(5)万用表的维护:万用表应水平放置使用,不得受振动,并注意防潮。使用完毕,应当把量程开关旋至电压最高档。若长时间不用,应将表内电池取出,以防电池腐蚀而损坏其他元件。

完形填空
A strange thing happened to me last Sunday. It was such a beautiful day that I decided to go for a  11  in the country. On the way back home,my car stopped. It was out of  12  on a lonely   road far from a town. I decided to walk until I found someone who could  13  me a gallon(加仑) or two of petrol. I had  14  almost a mile before I finally found a big house near the road. I was           15  to see it because it was starting to get dark. I  16  at the door and a little old lady with long white hair answered. She said, “I have been  17  for you a long time. Come in. Tea is almost ready.”
“But I only came for some petrol.” I answered. I couldn’t  18  what she was talking about.
“Oh, Alfred! Petrol? You used to  19  tea.”
I quickly  20  that I needed some petrol, but she didn’t seem to hear me. She just kept calling me Alfred and talking about how long it had been since she had seen me. She was acting very strangely and I was  21  to leave. As soon as she went to get tea, I went out of the house as fast as I could.  22  , there was another house down the road and I was able to buy several gallons of petrol. When I told the man about my  23 . He said,“Oh, that is Miss Emily. She lives by herself in that big house. She’s  24  but she wouldn’t hurt anyone. She is still waiting for the man she was supposed to marry thirty years ago. The day before their  25  he left home and never came back because of the war.”
小题1:
A.walkB.holidayC.driveD.picnic
小题2:
A.workB.petrolC.orderD.sight
小题3:
A.buyB.borrowC.sellD.send
小题4:
A.restedB.stoppedC.steppedD.walked
小题5:
A.amazedB.pleasedC.surprisedD.tired
小题6:
A.beatB.stoodC.knockedD.struck
小题7:
A.waitingB.searchingC.longingD.looking
小题8:
A.orderB.hearC.imagineD.remember
小题9:
A.likeB.haveC.drinkD.make
小题10:
A.explainedB.realizedC.noticedD.discovered
小题11:
A.excitedB.anxiousC.worriedD.amazed
小题12:
A.FortunatelyB.LatelyC.ImmediatelyD.Personally
小题13:
A.expressionB.ideaC.scheduleD.experience
小题14:
A.kindB.funnyC.strangeD.angry
小题15:
A.marriageB.journeyC.planD.wedding
多项选择题