问题 问答题 简答题

说明检测端安全栅和操作端安全栅的构成基本原理。

答案

参考答案:

检测端安全栅用于为两线制变送器进行隔离式供电,并将变送器送来的4-20mADC转换成隔离的并与之成正比的4-20mADC或1-5VDC的信号,而且在故障状态下,可限制其电流和电压值,使进入危险场所的能量限制在安全额定值以下。它是由直流/交流转换器、整波滤波器、调制器、解调放大器、隔离变压器及限能器等组成。信号的传送与转换过程是:变送器传来的4-20mADC信号由调制器利用直流/交流转换器提供的供电方波调制成矩形波交流信号,该信号经信号隔离变压器进行信号隔离后送至解调放大器,由解调放大器将矩形波信号转换为4-20mADC和1-5VDC信号,供安全区域内的仪表使用。限能器的作用是限制流入危险区域的高电压或大电流,将流入危险区域的能量限制在安全额定值以内。

操作端安全栅是由直流/交流转换器、调制器、隔离变压器、解调放大器、整流滤波器和限能器组成。它是将控制仪表送来的4-20mA信号由调制器利用直流/交流转换器提供的供电转换为交流方波信号,该信号由信号隔离变压器隔离后送至解调放大器,由解调放大器将此方波信号重新还原为4-20mADC信号,经限能器送至现场。限能器的作用仍是限流和限压,防止高电压或大电流进入现场。

阅读理解

阅读理解

     I made a pledge(誓言) to myself on the way down to the vacation beach cottage. For two weeks

I would try to be a loving husband and father. Totally loving. No ifs, ands or buts.

     The idea had come to me as I listened to a talk on my car radio. The speaker was quoting a Biblical

(圣经的)passage about husbands being thoughtful of their wives. Then he went on to say, "Love is an

act of will. A person can choose to love." To myself, I had to admit that I had been a selfish husband.

Well, for two weeks that would change. And it did. Right from the moment I kissed Evelyn at the door

and said, "That new yellow sweater(套头衫) looks great on you."  "Oh, Tom, you noticed, "she said,

surprised and pleased. Maybe a little puzzled.  After the long drive, I wanted to sit and read. Evelyn

suggested a walk on the beach. I started to refuse, but then I thought, "Evelyn's been alone here with

the kids all week and now she wants to be alone with me. "We walked on the beach while the children

flew their kites.  So it went. Two weeks of not calling the Wall Street firm where I am a director; a visit

to the shell museum though I usually hate museums. Relaxed and happy, that's how the whole vacation

passed. I made a new pledge to keep on remembering to choose love.  

     There was one thing that went wrong with my experiment, however. Evelyn and I still laugh about

it today. On the last night at our cottage, preparing for bed, Evelyn stared at me with the saddest

expression. "What's the matter?" I asked her. "Tom," she said in a voice filled with distress(悲痛), "do

you know something I don't?"  "What do you mean?"  "Well…that checkup(体检) I had several weeks

ago…our doctor…did he tell you something about me?Tom, you've been so good to me…am I dying?" 

It took a moment for it all to sink in. Then I burst out laughing.  "No, honey," I said, wrapping her in my arms. "You're not dying; I'm just starting to live."

1. From the story we may infer that Tom drove to the beach cottage ________.

A. with his family  

B.  with Evelyn    

C. alone    

D. with his children

2. During the two weeks on the beach, Tom showed more love to his wife because ____.

A. she looked lovely in her new clothes    

B.  he had made a lot of money in his Wall Street firm

C. he was determined to be a good husband        

D. she was seriously ill

3. The author says, "There was one thing that went wrong with my experiment. "What was the one

     thing that went wrong?

A. He praised her sweater, which puzzled her.

B. She insisted on visiting a museum, which he hated.

C. He knew something about her illness but didn't tell her.

D. He was so good to her that she thought she must be dying.

4. By saying "I'm just starting to live," Tom means that ________.

A. he is just beginning to understand the real meaning of life

B. he is just beginning to enjoy life as a loving husband

C. he lived an unhappy life before and is now starting to change

D. he is beginning to feel regret for what he did to his wife before

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