范文一:惠斯通电桥 实验
实验3 惠斯通电桥
测量电阻常用伏安法和电桥法。由于伏安法测量中电表的内阻会对测量带来附加误差~测量精度受到限制。电桥是用比较法测量电阻的仪器~电桥测量的特点是灵敏、准确和使用方便。电桥分为直流电桥和交流电桥两大类。电桥不但可以测量电阻、电容、电感~还可以通过测量传感器的电阻变化~间接测量温度、压力、应变、真空度和加速度等非电学量~所以被广泛应用于现代工业自动控制~非电量电测法中。
直流电桥又可分为平衡电桥和非平衡电桥。平衡电桥采样调节电桥平衡测量待测电阻值~主要用于测量处于稳定状态的物理量,非平衡电桥直接测量电桥的输出~通过计算得到物理量的值~非平衡电桥主要用于测量处于变化状态的物理量。本实验的惠斯通电桥为
161010,,,直流电桥~又名直流单臂电桥~主要用于测量中等数量级电阻,量级,~虽然它的这种功能在生产和科研的大多数场合中已被其他仪器,如万用表,所取代~但是电桥电路却在自动检测~自动控制等多个领域得到广泛应用。因此~本实验不仅是要学会组装电桥测量电阻~了解基本实验方法——平衡法和比较法~更重要的是通过测量电阻掌握调整电桥平衡方法~从而了解平衡电桥的基本特性~为在自动控制以及检测电路中应用电桥电路打下一个良好基础。
,611010,,,对于低电阻,量级,的测量~要考虑其接触电阻、导线电阻的影响~应
710,使用开尔文电桥即直流双臂电桥~对于高电阻,量级,则可考虑用冲击电流计等方法。
【实验目的】
1. 掌握惠斯通电桥的结构特点和测量电阻的原理。
2. 练习按电路图连接线路。
3. 掌握调整电桥平衡的方法。
school)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and magazines, fires burnt down. In 1938, the Japanese learned that the national Government established in XI Tang Tomb rotten "clip" taxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao was burned several houses. 1938 new morning of September 18, the Japanese team went to the countryside "sweep" from the kaiyang village line to Tung Yang Jia Qiao yan Temple wall and met Yang Jia溇 Zhou Dana (male) weeks because of long-term illness and can't work in the fields, the Japanese see his face from scratch without calluses, regard him as "Shina", thrust a knife at the scene of his death. The body was stabbed 7 times, wound 13. The same day, Trang bang village heard the Japanese come to "mop-up" are hiding, mother of 9 Zhou Guanbao Zhang Aying to drill a "dry mound", was discovered by the Japanese, a shot in the end. The same day, is 7 zhouhaijiangzhi grandfather Zhou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In March 1939, the Japanese army in Yan Tomb raiding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing 11 people on the River, East meeting point in wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese go speak the Shanghai dialect, later to be called Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or six thousand, water and land go hand in hand "mop-up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its child Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, and players Jin Fuqin, and Shen Baosheng, six people received Wujiang underground County Government notification
4. 研究电桥灵敏度。
5. 学习系统误差的分析方法,初步掌握消除和减小部分
系统误差的方法。
【实验原理】
1. 惠斯通电桥的结构及测量原理
(1)惠斯通电桥的结构
图1是惠斯通桥的结构图。4个电阻连成四RRRR,,,120x
边形,称为电桥的4个臂,其中称为比例臂,为待RR,R12x图1 惠斯通电桥原理图 测臂,为比较臂。四边形的对角线AB接上电源,称为 R0
电桥的“电源对角线”,E为电源。四边形的另一个对角线CD连有检流计,称为“桥”,
为阻值较大的可变电阻,在电桥不平衡时取大阻值保护检流计,在电桥接近平衡时减R保护
等于零。 少其阻值以提高检流计的灵敏度,电桥平衡时取R保护
(2)惠斯电桥处通电桥的测量原理。
在图1中,将电源接通后,当C、D两点之间的电位不相等时,桥路中的电流I,0,g
I,0此时检流计的指针发生偏转,当C、D两点之间的电位相等时,桥路中,此时检流g计指针指零,这时我们称于平衡状态。当电桥平衡时我们可以得到下列公式:
IRIRIRIRIIII,,,,,,, RRRxRRRRR120120120xx
RRx1RRRR,于是 或者 (1) ,x201RR02
(1)式即为惠斯通电桥的平衡方程。它说明,电桥平衡时,电桥相对臂电阻的乘积
R相等,这就是电桥的平衡条件。根据电桥的平衡方程,的计算式为 x
R1 (2) RRKR,,x00R2
ple on the River, East meeting point in wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese11 peoMarch 1939, the Japanese army in Yan Tomb raiding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing day, is 7 zhouhaijiangzhi grandfather Zhou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In d. The same up" are hiding, mother of 9 Zhou Guanbao Zhang Aying to drill a "dry mound", was discovered by the Japanese, a shot in the en-of his death. The body was stabbed 7 times, wound 13. The same day, Trang bang village heard the Japanese come to "moprust a knife at the scene term illness and can't work in the fields, the Japanese see his face from scratch without calluses, regard him as "Shina", th-Zhou Dana (male) weeks because of long 溇lage line to Tung Yang Jia Qiao yan Temple wall and met Yang Jiang vilwas burned several houses. 1938 new morning of September 18, the Japanese team went to the countryside "sweep" from the kaiyatablished in XI Tang Tomb rotten "clip" taxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao gazines, fires burnt down. In 1938, the Japanese learned that the national Government esschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and maand players Jin Fuqin, and Shen Baosheng, six people received Wujiang underground County Government notification child Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-usand, water and land go hand in hand "mopx thogo speak the Shanghai dialect, later to be called Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or si 2
R1(2)成为平衡电桥测量电阻的原理,其中称为比率值,这也是称为比RR,K,12R2
例臂的原因。
由于检流计在测量过程中起判断桥路有无电流的作用,只要检流计有足够的灵敏度来反映桥路电流的变化,则的测量结果与检流计精度无关,通常用标准电阻箱,RRRR,,x120
由于标准电阻可以制作得比较精密,所以利用电桥的平衡原理测电阻的准确度可以很高,大大优于伏安法测电阻,这也是电桥应用广泛的一个重要原因。
2. 电桥的灵敏度
电桥是否达到平衡,是以桥路中有无电流来进行判断的,而桥路中有无电流又是以检流计的指针是否发生偏转来确定的,但检流计灵敏度总是有限的,这就限制了对电桥是否达到平衡的判断。另外,检流计指针偏转小于0.2格时,很难察觉出指针的偏转。一般来讲检流计指针有0.2格的偏转人眼便可察觉。因此,引入电桥灵敏度问题。
,n检流计灵敏度定义为:电流变化量所引起的检流计指针偏转格数与电流变化量
的比值,即 ,Ig
,nS, (3) 检流计,Ig
电桥相对灵敏度定义为:在处于平衡的电桥里,其测量臂电阻R有一个相对的变量x
,R,Rxx,n,则由此而引起的检流计指针偏转格数与的比值为: RRxx
,,nnS,, (4) 相对,,RRx0
RRx0
电桥的相对灵敏度习惯又简称为电桥灵敏度,用S表示,S越大,说明电桥越灵敏。下面我们讨论影响S的因素。
将(3)式代入(4)式。
up" are hiding, mother of 9 Zhou Guanbao Zhang Ayin-mes, wound 13. The same day, Trang bang village heard the Japanese come to "mopace from scratch without calluses, regard him as "Shina", thrust a knife at the scene of his death. The body was stabbed 7 titerm illness and can't work in the fields, the Japanese see his f-Zhou Dana (male) weeks because of long 溇ple wall and met Yang Jiaf September 18, the Japanese team went to the countryside "sweep" from the kaiyang village line to Tung Yang Jia Qiao yan Teming otaxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao was burned several houses. 1938 new morn s, fires burnt down. In 1938, the Japanese learned that the national Government established in XI Tang Tomb rotten "clip"gazineschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and mang, six people received Wujiang underground County Government notificationhild Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, and players Jin Fuqin, and Shen Baoshec up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-mopalled Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or six thousand, water and land go hand in hand "be c wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese go speak the Shanghai dialect, later to ding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing 11 people on the River, East meeting point inmb raihou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In March 1939, the Japanese army in Yan Tog to drill a "dry mound", was discovered by the Japanese, a shot in the end. The same day, is 7 zhouhaijiangzhi grandfather Z3
,Ig (5) SSR,,,x检流计,Rx
因和变化很小,可用其偏微商形式表示 ,I,Rgx
,Ig (6) SSR,,,x检流计,Rx
利用基尔霍夫定律联立方程,经过必要的推导、整理、化简,可以得到
SE,检流计 (7) S,,,,,RR012RRRRR,,,,,,,,,,,,xg120RRx2,,,,
由(7)式分析可知:
(1)电桥灵敏度S与检流计灵敏度S成正比,检流计灵敏度越高,则电桥的灵敏检流计
度越高。
(2)电桥灵敏度与电源电压E成正比,在确保桥臂电阻安全稳定的前提下,可以通过适当提高电源电压来提高电桥灵敏度。
RRRR,,,(3)电桥灵敏度随四个桥臂电阻总阻值的增大而减小,随着,,120x,,RR01,的增大而减小。桥臂电阻选得过大,将大大降低电桥灵敏度,R和R阻值相,,21RR2x,,
差太大,也会降低其灵敏度。
以上分析,对我们在实际工作中提高电桥灵敏度提供了理论依据。一般成品电桥为了进一步提高其测量灵敏度,通常都有外接检流计与外接电源接线柱,以接入灵敏度更高的检流计或谨慎而适当地提高电源电压。
3. 惠斯通电桥存在的系统误差讨论
R1RRR,,(1)在本实验中,均选择0.1级的电阻箱,由公式可得,由RR,,120x0R2RRR,,R仪器误差引起的测量的B类不确定度: x120
222222URREREEER,,,,,,,,,,0.1%0.1%0.1%,,,,,,,,,,,,,,BxxRxRRRxx120
usand, water and land go hand in hand "mopx thogo speak the Shanghai dialect, later to be called Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or si ple on the River, East meeting point in wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese11 peoMarch 1939, the Japanese army in Yan Tomb raiding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing day, is 7 zhouhaijiangzhi grandfather Zhou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In d. The same up" are hiding, mother of 9 Zhou Guanbao Zhang Aying to drill a "dry mound", was discovered by the Japanese, a shot in the en-of his death. The body was stabbed 7 times, wound 13. The same day, Trang bang village heard the Japanese come to "moprust a knife at the scene term illness and can't work in the fields, the Japanese see his face from scratch without calluses, regard him as "Shina", th-Zhou Dana (male) weeks because of long 溇lage line to Tung Yang Jia Qiao yan Temple wall and met Yang Jiang vilwas burned several houses. 1938 new morning of September 18, the Japanese team went to the countryside "sweep" from the kaiyatablished in XI Tang Tomb rotten "clip" taxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao gazines, fires burnt down. In 1938, the Japanese learned that the national Government esschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and maand players Jin Fuqin, and Shen Baosheng, six people received Wujiang underground County Government notification child Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-4
即 (8) URR,0.17%,,Bxx
,,RRRRR01011(2)由于是的倒数,容易证明当时,有最小值,所以,RR,,1,,12RRRRRx22x2,,
时电桥灵敏度更高。阻值选取一样,也存在实际阻值不等,由此产生的系统RR,RR,1212
误差,可以通过交换和分别测量两次的方法来消除,电桥平衡时两次测得的值分RRR0x0
,R别记为, R00
RR12,则, RR,RR,x0x0RR21
,RRR,所以 (9) x00
当为0.1级的电阻箱,由此引起的测量的B类不确定度 RR0x
221122,,,,URREREER ,,,,,,,,0.05%0.05%,,,,,,BxxRxRx,,,,,x0R022,,,,
RRR,0.071%即 (10) ,,Bxx
(3)一般检流计指针有0.2格的偏转我们才能够观察到,则由此而引起的B类不确定度
0.2UR,= (11) x灵S
3当S为10量级,则U最大为 灵
UR=0.02%, x灵
3与(8)、(10)或比较,当S优于10时,可以不考虑灵敏度引起的系统误差。
(4)在实际运用里,由于电桥桥臂中可能存在很小的寄生热电势,这样一来,即使I,0,电桥也未必满足平衡条件,消除这一系统误差的方法是,改变电源E的方向,分g
R别测量两次,将得到值取平均。 x
【实验仪器】
up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-mopalled Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or six thousand, water and land go hand in hand "be c wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese go speak the Shanghai dialect, later to ding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing 11 people on the River, East meeting point inmb raihou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In March 1939, the Japanese army in Yan Tog to drill a "dry mound", was discovered by the Japanese, a shot in the end. The same day, is 7 zhouhaijiangzhi grandfather Zup" are hiding, mother of 9 Zhou Guanbao Zhang Ayin-mes, wound 13. The same day, Trang bang village heard the Japanese come to "mopace from scratch without calluses, regard him as "Shina", thrust a knife at the scene of his death. The body was stabbed 7 titerm illness and can't work in the fields, the Japanese see his f-Zhou Dana (male) weeks because of long 溇ple wall and met Yang Jiaf September 18, the Japanese team went to the countryside "sweep" from the kaiyang village line to Tung Yang Jia Qiao yan Teming otaxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao was burned several houses. 1938 new morn s, fires burnt down. In 1938, the Japanese learned that the national Government established in XI Tang Tomb rotten "clip"gazineschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and mang, six people received Wujiang underground County Government notificationhild Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, and players Jin Fuqin, and Shen Baoshec5
ZX21型电阻箱,检流计,直流稳压电源,M-8308型数字万用表、待测电阻。
【实验说明】
1、 电阻箱
电阻箱是实验室常用来获得比较精确电阻值的可变电阻器,它由若干个数值准确的固定电阻元件(用高稳定锰铜合金绕制)组合而成,并按一定的方式连接于转换开关上,转动旋钮即可得到不同阻值。
电阻箱精度等级可分为0.02级、0.05级、0.1级、0.2级和0.5级5个级别。若电阻a
箱读数为R,则该仪器不确定度为
,,,Ra%仪
电阻箱的额定功率:如果未特别标明,则以0.25W来计算其最大允许电流。例如,若
,使用100档,则该档电阻允许通过的最大电流为
0.25wIA,,0.05 max100,
实验室常用的ZX21型旋转式电阻箱(0.1级,额定功率0.25w)各档允许通过的最大电流计算于表1,长时间使用允许的额定电流约为最大允许电流的75%。使用时必须给予足够的重视。
表1 ZX21型电阻箱最大允许电流与额定电流一览表
负载情况 ,电阻档() 0.1 1 10 100 1000 10000
最大允许电流(A) 短时间使用 1.6 0.5 0.16 0.05 0.016 0.005
额定电流(A) 长时间使用 1.2 0.4 0.12 0.04 0.012 0.004
2. 检流计
uA检流计是一个微定表,绝对不允许通过的电流太大,在本实验中主要采取下列保,,
R护措施,首先把R置于最大档位,其次将电源电压E调至很小,并把桥臂电阻选保护保护
择预置于接近平衡的参数,方可接通检流计。电桥平衡后,将调至零,逐步提高电源电压E。检流计调零也是使用过程中必须经常关注的。
3. 数字万用表。
go speak the Shanghai dialect, later to be called Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or si ple on the River, East meeting point in wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese11 peoMarch 1939, the Japanese army in Yan Tomb raiding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing day, is 7 zhouhaijiangzhi grandfather Zhou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In d. The same up" are hiding, mother of 9 Zhou Guanbao Zhang Aying to drill a "dry mound", was discovered by the Japanese, a shot in the en-of his death. The body was stabbed 7 times, wound 13. The same day, Trang bang village heard the Japanese come to "moprust a knife at the scene term illness and can't work in the fields, the Japanese see his face from scratch without calluses, regard him as "Shina", th-Zhou Dana (male) weeks because of long 溇lage line to Tung Yang Jia Qiao yan Temple wall and met Yang Jiang vilwas burned several houses. 1938 new morning of September 18, the Japanese team went to the countryside "sweep" from the kaiyatablished in XI Tang Tomb rotten "clip" taxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao gazines, fires burnt down. In 1938, the Japanese learned that the national Government esschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and maand players Jin Fuqin, and Shen Baosheng, six people received Wujiang underground County Government notification child Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-usand, water and land go hand in hand "mopx tho6
有关数字万用表的详细介绍,请参见附录。
【预习思考题】
1. 电桥灵敏度的定义是什么,实验中是怎样测量灵敏度的,影响电桥灵敏度的因素
有哪些,
2. 简述调整电桥平衡的方法。
【实验内容】
1. 用数字万用表适当的量程,粗测待测电阻的阻值。 Rx
2. 按图2所示的惠斯通电桥电路图组装惠斯通电桥,测量待测电阻的阻值,并同时测量电桥灵敏度。 Rx
(1)检流计调零。
(2)电源E调至很小,0.1V-0.3V。
90000.0,)R置于,检流计量程置于“”档。 (310,A保护
(4)按图2所示连接测量电路,但特别注意与电源正极相联的导线暂不连接。
(5)按表2所给数据设定的的值,并根据的粗测RR,R12x
图2 惠斯通电桥测量电路
R图 1值及比率预置R的值。 0R2
R(6)检查无误后,再最后连接电源正极。调整电桥平衡,测量值,并同时测量电x桥灵敏度,按下列方式进行:
R? 在上述工作的基础上,调整,使电桥平衡。 0
R? 逐步减小R,直至R=0,调整,使电桥平衡。 保护保护0
R? 检流计由“10,A”档调到“1,A”档,调整,使电桥平衡。 0
RR? 缓慢增加E的数值,适度调整,确保检流计不超过量程,将E调至5V,调整,00
R使电桥平衡,记录此时的值。 0
ding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing 11 people on the River, East meeting point inmb raihou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In March 1939, the Japanese army in Yan Tog to drill a "dry mound", was discovered by the Japanese, a shot in the end. The same day, is 7 zhouhaijiangzhi grandfather Zup" are hiding, mother of 9 Zhou Guanbao Zhang Ayin-mes, wound 13. The same day, Trang bang village heard the Japanese come to "mopace from scratch without calluses, regard him as "Shina", thrust a knife at the scene of his death. The body was stabbed 7 titerm illness and can't work in the fields, the Japanese see his f-Zhou Dana (male) weeks because of long 溇ple wall and met Yang Jiaf September 18, the Japanese team went to the countryside "sweep" from the kaiyang village line to Tung Yang Jia Qiao yan Teming otaxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao was burned several houses. 1938 new morn s, fires burnt down. In 1938, the Japanese learned that the national Government established in XI Tang Tomb rotten "clip"gazineschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and mang, six people received Wujiang underground County Government notificationhild Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, and players Jin Fuqin, and Shen Baoshec up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-mopalled Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or six thousand, water and land go hand in hand "be c wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese go speak the Shanghai dialect, later to7
,,n5.0? 从最小位开始改变,直至检流计指针的编转格数格(以检流计最上边R0
一排刻度的最小分度为1.0格),记录下的改变量以及检流计相对平衡位置时的偏R,R00
,n转格数。
90000.0,将E减小至0.1V-0.3V,R置于,检流计置于“”档,根据RR,10,A保护12值,预置,重复。如此反复多次完成表2的测量工作。调整过程也是逐步提高电Rae,0
桥灵敏度的过程。
表2 测量待测电阻及电桥灵敏度
EVR,R,R,,,RR(),,n(格) S ,,,,,,,,,,1200x
1000.0 1000.0
1000.0 100.0 5.0
100.0 1000.0
100.0 100.0 3. 用惠斯通电桥交换法测量电阻 Rx
表3 用交换法测待测电阻 Rx
,EVR,R,R, R(), ,,,,,,,,,,R ,,120x0
1000.0 1000.0
5.0 100.0 100.0
20.0 20.0 【数据处理】
R1. 用数字万用表粗测待测电阻,计算B类不确定度,写出标准表达式。 x
URURR2. 不同比率测量,计算出R及,利用(8)式得到, ,,,,AxBxxx
22RURURUR,,写出标准表达式。 ,,,,,,xCxAxBx
up" are hiding, mother of 9 Zhou Guanbao Zhang Aying to drill a "dry mound", was discovered by the Japanese, a shot in the en-of his death. The body was stabbed 7 times, wound 13. The same day, Trang bang village heard the Japanese come to "moprust a knife at the scene term illness and can't work in the fields, the Japanese see his face from scratch without calluses, regard him as "Shina", th-Zhou Dana (male) weeks because of long 溇lage line to Tung Yang Jia Qiao yan Temple wall and met Yang Jiang vilwas burned several houses. 1938 new morning of September 18, the Japanese team went to the countryside "sweep" from the kaiyatablished in XI Tang Tomb rotten "clip" taxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao gazines, fires burnt down. In 1938, the Japanese learned that the national Government esschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and maand players Jin Fuqin, and Shen Baosheng, six people received Wujiang underground County Government notification child Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-usand, water and land go hand in hand "mopx thogo speak the Shanghai dialect, later to be called Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or si ple on the River, East meeting point in wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese11 peoMarch 1939, the Japanese army in Yan Tomb raiding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing day, is 7 zhouhaijiangzhi grandfather Zhou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In d. The same 8
,n 3. 用公式,计算出灵敏度S,S取两位有效数字。 S,,R0
R0
4. 交换法则,计算出及,利用(10)式得到, URURRR,,,,AxBxxx
22写出标准表达式。 RURURUR,,,,,,,,xCxAxBx
【思考题】
1. 从研究电桥灵敏度的实验数据中,你能分析出有哪些因素影响着电桥的灵敏度,
2. 在电桥平衡的调节过程中,你是如何依据检流计指针的偏转变化来调节比较臂,R0使电桥趋于平衡的,
,3. 如果用电桥测一毫安表内阻(量程3mA,内阻约为30),应该特别注意些什么,怎样选择参数,才能保证测量顺利完成,
wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese go speak the Shanghai dialect, later to ding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing 11 people on the River, East meeting point inmb raihou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In March 1939, the Japanese army in Yan Tog to drill a "dry mound", was discovered by the Japanese, a shot in the end. The same day, is 7 zhouhaijiangzhi grandfather Zup" are hiding, mother of 9 Zhou Guanbao Zhang Ayin-mes, wound 13. The same day, Trang bang village heard the Japanese come to "mopace from scratch without calluses, regard him as "Shina", thrust a knife at the scene of his death. The body was stabbed 7 titerm illness and can't work in the fields, the Japanese see his f-Zhou Dana (male) weeks because of long 溇ple wall and met Yang Jiaf September 18, the Japanese team went to the countryside "sweep" from the kaiyang village line to Tung Yang Jia Qiao yan Teming otaxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao was burned several houses. 1938 new morn s, fires burnt down. In 1938, the Japanese learned that the national Government established in XI Tang Tomb rotten "clip"gazineschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and mang, six people received Wujiang underground County Government notificationhild Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, and players Jin Fuqin, and Shen Baoshec up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-mopalled Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or six thousand, water and land go hand in hand "be c9
附录 M-8308型数字万用表
万用表分机械式和数字式。机械式万用表大多数通过离散的电学元件组成,利用线圈在磁场中偏转带动指针指示物理量的大小。数字式万用表大多数采用传感器、模数转换来测量物理量,通过发光二极管或液晶显示屏显示结果。
万用表可以测量直流电压、交流电压、直流电流、交流电流、电阻、二极管及三极管的测试等。在电学实验中万用表可以用来判定线路故障,如电路没接入电源,则可以用欧姆档测试导线是否断裂;如电路有电源,则可以用电压档测试有无电压来判定线路故障。
图3是一种小型数字式万用表M-8308型。在操作万用表之前需要熟悉每一种控制,以避免使用不当及减少测量错误、减小万用表的损坏和人生伤害的可能性。
1. 盘的介绍
(1)功能及量程开关
图4中标示1的部分是测量功能转换及量程选择
的开关。这部分位于面板盘的中心。通过改变开关1
的位置可以测量直流电压、电阻、判定二极管极性、
测量三极管的放大倍数、测量10A的大电流、测量直
流电流、测量交流电压。在每一个功能中又可以转换
量程。当开关转到“OFF”用于切断电源,平时不用时
应将开关扳到此以节约电源。
(2)显示
面板盘标示2的部分为测量值的显示位置。
(3)公共地端
插座3为公共端用于接地(一般接万用表的黑表笔)。
(4)电压、欧姆、毫安插座
插座4和3用于测量电压、电阻、电流(10A除外)。
(5)大电流10A插座
插座5和3用于测量大电流(10A以内)。
2. 仪器不确定度
不同的测量其精度等级不一样,因而仪器的不确定度也不一样。本实验主要用来测量电阻,因此我们只考虑测量电阻产生的仪器不确定度。
表2 测量电阻的仪器不确定度
量程 分辨率 精度(一年内18——28?)
d. The same up" are hiding, mother of 9 Zhou Guanbao Zhang Aying to drill a "dry mound", was discovered by the Japanese, a shot in the en-of his death. The body was stabbed 7 times, wound 13. The same day, Trang bang village heard the Japanese come to "moprust a knife at the scene term illness and can't work in the fields, the Japanese see his face from scratch without calluses, regard him as "Shina", th-Zhou Dana (male) weeks because of long 溇lage line to Tung Yang Jia Qiao yan Temple wall and met Yang Jiang vilwas burned several houses. 1938 new morning of September 18, the Japanese team went to the countryside "sweep" from the kaiyatablished in XI Tang Tomb rotten "clip" taxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao gazines, fires burnt down. In 1938, the Japanese learned that the national Government esschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and maand players Jin Fuqin, and Shen Baosheng, six people received Wujiang underground County Government notification child Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-usand, water and land go hand in hand "mopx thogo speak the Shanghai dialect, later to be called Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or si ple on the River, East meeting point in wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese11 peoMarch 1939, the Japanese army in Yan Tomb raiding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing day, is 7 zhouhaijiangzhi grandfather Zhou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In 10
200Ω 100mΩ (0.8%×读数,2D) ,
2000Ω 1Ω (0.8%×读数,2D) ,
20kΩ 10Ω (0.8%×读数,2D) ,
200kΩ 100Ω (0.8%×读数,2D) ,
2000kΩ 1kΩ (1%×读数,2D) ,
说明:最大开路电压为2.8V。
3. 注意事项
? 为了避免损伤或损害万用表,不要测试电压超过500V的电压。
? 在使用万用表之前,请检查测试导线、连接、探针是否有绝缘破损或断开。
? 在测试电压时请注意一定要将量程开关扳到电压档,否则将烧坏保险管或损害万用表。
? 在测试电阻时一定要保证待测电阻不带电。
? 安全标志符号
~ 此标记表明本操作一定要遵守操作规范以避免损坏仪器设备或对人身造成损害。
WARNING 警告:此标记意味着可能会造成伤害。它要求操作时应谨慎,不正确的操
作可能会导致人身伤害。
CAUTION 注意:此标记意味着可能会造成伤害。它要求操作时应谨慎,不正确的操
作可能会导致仪器全部或部分损坏。
500V max
此标记忠告用户测试点的电压相对于接地不要超过500V。
此标记意味着测试点的电压较高,为了最大的安全起见,不要用手接触。
hou Yingbao to escape the Japanese army, was found on the road, a shot in the end. In March 1939, the Japanese army in Yan Tog to drill a "dry mound", was discovered by the Japanese, a shot in the end. The same day, is 7 zhouhaijiangzhi grandfather Zup" are hiding, mother of 9 Zhou Guanbao Zhang Ayin-mes, wound 13. The same day, Trang bang village heard the Japanese come to "mopace from scratch without calluses, regard him as "Shina", thrust a knife at the scene of his death. The body was stabbed 7 titerm illness and can't work in the fields, the Japanese see his f-Zhou Dana (male) weeks because of long 溇ple wall and met Yang Jiaf September 18, the Japanese team went to the countryside "sweep" from the kaiyang village line to Tung Yang Jia Qiao yan Teming otaxes, tax officers live in 8 of Yan Dong village farmers home, troops at night, Yao was burned several houses. 1938 new morn s, fires burnt down. In 1938, the Japanese learned that the national Government established in XI Tang Tomb rotten "clip"gazineschool)], 4 4 house building as well as more than 1000 copies of books, more than 10 kinds of collection of newspapers and mang, six people received Wujiang underground County Government notificationhild Niu Jun (strict Tomb seventh district Chang) and the District Assistant Yu Xuchu, and players Jin Fuqin, and Shen Baoshec up" jiaxing area west of the railway, Yan Tomb area fall. March 6, Niu Shan (County Government II section chief) carrying its-mopalled Gu Tong as "kill left." On January 18, 1943, the elves, five thousand or six thousand, water and land go hand in hand "be c wood qiaotu in the afternoon killing 4 people on the Riverside. Gu Tong is a Japanese go speak the Shanghai dialect, later to ding, has arrested 16 people, in fengqiao cigarettes this morning bang, killing 11 people on the River, East meeting point inmb rai11
范文二:惠斯通电桥实验数据 惠斯通电桥实验
实验3 惠斯通电桥
测量电阻常用伏安法和电桥法。由于伏安法测量中电表的内阻会对测量带来附加误差,测量精度受到限制。电桥是用比较法测量电阻的仪器,电桥测量的特点是灵敏、准确和使用方便。电桥分为直流电桥和交流电桥两大类。电桥不但可以测量电阻、电容、电感,还可以通过测量传感器的电阻变化,间接测量温度、压力、应变、真空度和加速度等非电学量,所以被广泛应用于现代工业自动控制,非电量电测法中。
直流电桥又可分为平衡电桥和非平衡电桥。平衡电桥采样调节电桥平衡测量待测电阻值,主要用于测量处于稳定状态的物理量;非平衡电桥直接测量电桥的输出,通过计算得到物理量的值,非平衡电桥主要用于测量处于变化状态的物理量。本实验的惠斯通电桥为直流电桥,又名直流单臂电桥,主要用于测量中等数量级电阻(101 ~106 量级),虽然它的这种功能在生产和科研的大多数场合中已被其他仪器(如
1
万用表)所取代,但是电桥电路却在自动检测,自动控制等多个领域得到广泛应用。因此,本实验不仅是要学会组装电桥测量电阻,了解基本实验方法——平衡法和比较法,更重要的是通过测量电阻掌握调整电桥平衡方法,从而了解平衡电桥的基本特性,为在自动控制以及检测电路中应用电桥电路打下一个良好基础。
对于低电阻(10 ~10 量级)的测量,要考虑其接触电阻、导线电阻的影响,应使用开尔文电桥即直流双臂电桥,对于高电阻(10 量级)则可考虑用冲击电流计等方法。
【实验目的】
1. 掌握惠斯通电桥的结构特点和测量电阻的原理。 2. 练习按电路图连接线路。 3. 掌握调整电桥平衡的方法。
7
~6
1
4. 研究电桥灵敏度。
5. 学习系统误差的分析方法,初步掌握消除和减小部分系统误差的方法。
【实验原理】
1. 惠斯通电桥的结构及测量原理 (1)惠斯通电桥的结构
图1是惠斯通桥的结构图。4个电阻R1,R2,R0,Rx连成四
2
边形,称为电桥的4个臂,其中R1,R2称为比例臂,Rx为待测臂,R0为比较臂。四边形的对角线AB接上电源,称为
电桥的“电源对角线”,E为电源。四边形的另一个对角线CD连有检流计,称为“桥”,
R保护为阻值较大的可变电阻,在电桥不平衡时取大阻值保护检流计,在电桥接近平衡时减
图1 惠斯通电桥原理图
少其阻值以提高检流计的灵敏度,电桥平衡时取R保护等于零。
(2)惠斯电桥处通电桥的测量原理。
在图1中,将电源接通后,当C、D两点之间的电位不相等时,桥路中的电流Ig 0,此时检流计的指针发生偏转,当C、D两点之间的电位相等时,桥路中Ig 0,此时检流计指针指零,这时我们称于平衡状态。当电桥平衡时我们可以得到下列公式:
IR1R1 IR2R2,IRxRx IR0R0,IR1 IRx,IR2 IR0
于是
RxR0
R1R2
或者RxR2 R0R1
3
(1)
(1)式即为惠斯通电桥的平衡方程。它说明,电桥平衡时,电桥相对臂电阻的乘积相等,这就是电桥的平衡条件。根据电桥的平衡方程,Rx的计算式为
Rx
R1R2
R0 KR0 (2)
(2)成为平衡电桥测量电阻的原理,其中K 例臂的原因。
R1R2
称为比率值,这也是R1,R2称为比
由于检流计在测量过程中起判断桥路有无电流的作用,只要检流计有足够的灵敏度来反映桥路电流的变化,则Rx的测量结果与检流计精度无关,R1,R2,R0通常用标准电阻箱,由于标准电阻可以制作得比较精密,所以利用电桥的平衡原理测电阻的准确度可以很高,大大优于伏安法测电阻,这也是电桥应用广泛的一个重要原因。
2. 电桥的灵敏度
电桥是否达到平衡,是以桥路中有无电流来进行判断的,而桥路中有无电流又是以检流计的指针是否发生偏转来确定的,但检流计灵敏度总是有限的,这就限制了对电桥是否达到平衡的判断。另外,检流计指针偏转小于0.2格时,很难察觉出指针的偏转。一般来讲检流计指针有0.2格的偏转
4
人眼便可察觉。因此,引入电桥灵敏度问题。
检流计灵敏度定义为:电流变化量所引起的检流计指针偏转格数 n与电流变化量
Ig的比值,即
S检流计
n Ig
(3)
电桥相对灵敏度定义为:在处于平衡的电桥里,其测量臂电阻Rx有一个相对的变量
RxRx
,则由此而引起的检流计指针偏转格数 n与
RxRx
的比值为:
S相对
n RxRx
n R0R0
(4)
电桥的相对灵敏度习惯又简称为电桥灵敏度,用S表示,S越大,说明电桥越灵敏。下面我们讨论影响S的因素。
将(3)式代入(4)式。第一文库网
S S检流计 Rx
5
Ig Rx
(5)
因 Ig和 Rx变化很小,可用其偏微商形式表示
S S检流计 Rx
Ig Rx
(6)
利用基尔霍夫定律联立方程,经过必要的推导、整理、化简,可以得到
S
S检流计 E
,R1,R2,R0,Rx,,Rg
由(7)式分析可知:
(1)电桥灵敏度S与检流计灵敏度S度越高。
检流计
R1R0 2,,
RRx 2
(7)
成正比,检流计灵敏度越高,则电桥的灵敏
(2)电桥灵敏度与电源电压E成正比,在确保桥臂电阻安全稳定的前提下,可以通过适当提高电源电压来提高电桥灵敏度。
(3)电桥灵敏度随四个桥臂电阻总阻值,R1,R2,R0,Rx,的增大
6
而减小,随着 R1R0
, 的增大而减小。桥臂电阻选得过大,将大大降低电桥灵敏度,R1和R2阻值相 R2Rx
差太大,也会降低其灵敏度。
以上分析,对我们在实际工作中提高电桥灵敏度提供了理论依据。一般成品电桥为了进一步提高其测量灵敏度,通常都有外接检流计与外接电源接线柱,以接入灵敏度更高的检流计或谨慎而适当地提高电源电压。
3. 惠斯通电桥存在的系统误差讨论
(1)在本实验中,R1,R2,R0均选择0.1级的电阻箱,由公式Rx
R1R2
R0可得,由
R1,R2,R0仪器误差引起的测量Rx的B类不确定度:
UB,Rx,
Rx ERx Rx
Rx
即 UB
(2)由于
R0Rx
,
Rx, 0.17%Rx
7
R1
(8)
是
R1R2
的倒数,容易证明当
R1R0
时,所以R1 R2, 1 有最小值,R2
R2Rx
时电桥灵敏度更高。R1,R2阻值选取一样,也存在R1,R2
实际阻值不等,由此产生的系统误差,可以通过交换R0和Rx分别测量两次的方法来消除,电桥平衡时两次测得的R0值分别记为R0,R0
则Rx
R1R2
R0,Rx
R2R1
R0
所以
Rx
(9)
当R0为0.1级的电阻箱,由此引起的测量Rx的B类不确定度
8
Rx Rx
UB,
Rx,
Rx ERx
即 RB
,
Rx, 0.071%Rx
(10)
(3)一般检流计指针有0.2格的偏转我们才能够观察到,则由此而引起的B类不确定度
U灵=
0.2S
Rx (11)
当S为103量级,则U灵最大为
U灵=0.02% Rx
与(8)、(10)或比较,当S优于10时,可以不考虑灵敏度引起的系统误差。 (4)在实际运用里,由于电桥桥臂中可能存在很小的寄生热电势,这样一来,即使
Ig 0,电桥也未必满足平衡条件,消除这一系统误差的方法是,改变电源E的方向,分
3
别测量两次,将得到Rx值取平均。
9
【实验仪器】
ZX21型电阻箱,检流计,直流稳压电源,M-8308型数字万用表、待测电阻。 【实验说明】 1、 电阻箱
电阻箱是实验室常用来获得比较精确电阻值的可变电阻器,它由若干个数值准确的固定电阻元件(用高稳定锰铜合金绕制)组合而成,并按一定的方式连接于转换开关上,转动旋钮即可得到不同阻值。
电阻箱精度等级a可分为0.02级、0.05级、0.1级、0.2级和0.5级5个级别。若电阻箱读数为R,则该仪器不确定度为
仪 R a%
电阻箱的额定功率:如果未特别标明,则以0.25W来计算其最大允许电流。例如,若使用100 档,则该档电阻允许通过的最大电流为
Imax
0.05A
实验室常用的ZX21型旋转式电阻箱(0.1级,额定功率0.25w)各档允许通过的最大电流计算于表1,长时间使用允许的额定电流约为最大允许电流的75%。使用时必须给予足够的重视。
表1 ZX21型电阻箱最大允许电流与额定电流一览表
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2. 检流计
检流计是一个微定,uA,表,绝对不允许通过的电流太大,在本实验中主要采取下列保护措施,首先把R
保护
置于最大档位,其次将电源电压E调R保护至很小,并把桥臂电阻选
择预置于接近平衡的参数,方可接通检流计。电桥平衡后,将调至零,逐步提高电源电压E。检流计调零也是使用过程中必须经常关注的。
3. 数字万用表。
有关数字万用表的详细介绍,请参见附录。 【预习思考题】
1. 电桥灵敏度的定义是什么,实验中是怎样测量灵敏度的,影响电桥灵敏度的因素有哪些,
2. 简述调整电桥平衡的方法。 【实验内容】
1. 用数字万用表适当的量程,粗测待测电阻的阻值Rx。 2. 按图2所示的惠斯通电桥电路图组装惠斯通电桥,测量待测电阻Rx的阻值,并同时测量电桥灵敏度。
(1)检流计调零。
(2)电源E调至很小,0.1V-0.3V。
(3)R保护置于90000.0 ,检流计量程置于“10 A”档。 (4)按图2所示连接测量电路,但特别注意与电源正极相联的导线暂不连接。
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(5)按表2所给数据设定的R1,R2的值,并根据Rx的粗测
图2 惠斯通电桥测量电路
值及比率
R1R2
预置R0的值。
(6)检查无误后,再最后连接电源正极。调整电桥平衡,测量Rx值,并同时测量电桥灵敏度,按下列方式进行:
? 在上述工作的基础上,调整R0,使电桥平衡。 ? 逐步减小R保护,直至R保护=0,调整R0,使电桥平衡。
? 检流计由“10 A”档调到“1 A”档,调整R0,使电桥平衡。
? 缓慢增加E的数值,适度调整R0,确保检流计不超过量程,将E调至5V,调整R0,使电桥平衡,记录此时R0的值。
? 从R0最小位开始改变,直至检流计指针的编转格数
n 5.0格(以检流计最上边一排刻度的最小分度为1.0格),记录下R0的改变量 R0以及检流计相对平衡位置时的偏转格数 n。
将E减小至0.1V-0.3V,R保护置于90000.0 ,检流计置于“10 A”档,根据R1,R2
12
值,预置R0,重复a~e。如此反复多次完成表2的测量工作。调整过程也是逐步提高电桥灵敏度的过程。
表2 测量待测电阻及电桥灵敏度
3. 用惠斯通电桥交换法测量电阻Rx
表3 用交换法测待测电阻Rx
【数据处理】
1. 用数字万用表粗测待测电阻Rx,计算B类不确定度,写出标准表达式。 2. 不同比率测量Rx,计算出Rx及UA,Rx,,利用(8)式得到UB,Rx,,
UC,Rx,
写出Rx标准表达式。
3. 用公式S
n R0R0
,计算出灵敏度S,S取两位有效数字。
4. 交换法则Rx,计算出Rx及UA,Rx,,利用(10)式得到UB,Rx,,
UC,Rx,
Rx标准表达式。
【思考题】
1. 从研究电桥灵敏度的实验数据中,你能分析出有哪些因素影响着电桥的灵敏度, 2. 在电桥平衡的调节过程中,你
13
是如何依据检流计指针的偏转变化来调节比较臂R0,使电桥趋于平衡的,
3. 如果用电桥测一毫安表内阻(量程3mA,内阻约为30 ),应该特别注意些什么,怎样选择参数,才能保证测量顺利完成,
附录 M-8308型数字万用表
万用表分机械式和数字式。机械式万用表大多数通过离散的电学元件组成,利用线圈在磁场中偏转带动指针指示物理量的大小。数字式万用表大多数采用传感器、模数转换来测量物理量,通过发光二极管或液晶显示屏显示结果。
万用表可以测量直流电压、交流电压、直流电流、交流电流、电阻、二极管及三极管的测试等。在电学实验中万用表可以用来判定线路故障,如电路没接入电源,则可以用欧姆档测试导线是否断裂;如电路有电源,则可以用电压档测试有无电压来判定线路故障。
图3是一种小型数字式万用表M-8308型。在操作万用表之前需要熟悉每一种控制,以避免使用不当及减少测量错误、减小万用表的损坏和人生伤害的可能性。
1. 盘的介绍
(1)功能及量程开关
图4中标示1的部分是测量功能转换及量程选择的开关。这部分位于面板盘的中心。通过改变开关1的位置可以测量
14
直流电压、电阻、判定二极管极性、测量三极管的放大倍数、测量10A的大电流、测量直流电流、测量交流电压。在每一个功能中又可以转换量程。当开关转到“OFF”用于切断电源,平时不用时应将开关扳到此以节约电源。
(2)显示
面板盘标示2的部分为测量值的显示位置。 (3)公共地端
插座3为公共端用于接地(一般接万用表的黑表笔)。 (4)电压、欧姆、毫安插座
插座4和3用于测量电压、电阻、电流(10A除外)。 (5)大电流10A插座
插座5和3用于测量大电流(10A以内)。 2. 仪器不确定度
不同的测量其精度等级不一样,因而仪器的不确定度也不一样。本实验主要用来测量电阻,因此我们只考虑测量电阻产生的仪器不确定度。
表2 测量电阻的仪器不确定度
说明:最大开路电压为2.8V。
3. 注意事项
? 为了避免损伤或损害万用表,不要测试电压超过500V的电压。
? 在使用万用表之前,请检查测试导线、连接、探针是否
15
有绝缘破损或断开。
? 在测试电压时请注意一定要将量程开关扳到电压档,否则将烧坏保险管或损害万用表。
? 在测试电阻时一定要保证待测电阻不带电。
? 安全标志符号
警告:此标记意味着可能会造成伤害。它要求操作时应谨慎,不正确的操作可能会导致人身伤害。
注意:此标记意味着可能会造成伤害。它要求操作时应谨慎,不正确的操作可能会导致仪器全部或部分损坏。
500V。
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范文三:实验三用惠斯通电桥测量电阻
实验三 用惠斯通电桥测量电阻
一、实验目的
(1) 了解惠斯通电桥的结构,掌握惠斯通电桥的工作原理;
(2) 掌握用惠斯通电桥测量电阻;
二、实验仪器
电路实验台,导线若干,万用表一台
三、实验原理
电阻是电路的基本元件之一,电阻的测量是基本的电学测量。用伏安法测量电阻,虽然原理简单,但有系统误差。在需要精确测量阻值时,必须用惠斯通电桥,惠斯通电桥适宜于测量中值电阻(1~106Ω)。
惠斯通电桥的原理如图5.6-l所示。标准电阻R0、
R1、R2和待测电阻RX连成四边形,每一条边称
为电桥的一个臂。在对角A和C之间接电源E,
在对角B和D之间接检流计G。因此电桥由4
个臂、电源和检流计三部分组成。当开关KE和
KG接通后,各条支路中均有电流通过,检流计
图5.6-l 惠斯通电桥原理图 支路起了沟通ABC和ADC两条支路的作用,好
象一座“桥”一样,故称为“电桥”。适当调节
R0、R1和R2的大小,可以使桥上没有电流通过,即通过检流计的电流IG = 0,这时,B、D两点的电势相等。电桥的这种状态称为平衡状态。这时A、B之间的电势差等于A、D之间的电势差,B、C之间的电势差等于D、C之间的电势差。设ABC支路和ADC支路中的电流分别为I1和I2,由欧姆定律得
I1 RX = I2 R1
I1 R0 = I2 R2
两式相除,得
RXR?1
R0R2 (1)
(1)式称为电桥的平衡条件。由(1)式得
RX?
R1R0R2 (2)
即待测电阻RX等于R1 / R2与R0的乘积。通常将R1 / R2称为比率臂,将R0称为比较臂。
三、实验步骤
1、用实验台固定电阻,可调电阻,直流电源和毫安表搭建惠斯通电桥。
2、用万用表粗测待测电阻(用实验台上1K可调电阻旋到任意三个不同位置作为三个待测电阻)
3、毫安表选择最小量程,选取实验台的两个固定电阻分别为R1和R2,作为比率臂(通常选取比率为10的次方),电阻箱中四个旋钮电阻串联(×1000、×100、×10、×1Ω档)作为R0阻值调节,根据Rx粗测值,通过电阻箱四个旋钮从大到小逐步调节使的毫安表示数为0,记录此时R0的阻值。
4、根据测量结果填写下表
范文四:惠斯通电桥实验报告pdf
南昌 大学物 理实 验报告
课程名称: 惠斯通电桥
实验名称: 惠斯通电桥
学院: 眼视光学院 专业班级: 眼视光 151 班
学生姓名: 许春芸 学号: 6303615024
实验地点: 210 座位号: 30 座
实验时间: 第8周星期 6 上午10点10开始
一、实验目的:
1.掌握电桥测电阻的原理和方法。
2.了解减小测电阻误差的一般方法。
二、实验原理: 惠斯通电桥的电路四个电阻 R1.R2.R3.Rx 连成一个四边形,每一条边称作电桥的一个臂,对角 A 和 C 加上电源 E, 对角
B 和 D 之间连接检流计 G,所谓桥就是指 BD 这条对角线,它的作用就是将桥的两个端点的电势直接进行比较。 当 B.D 两点 电势相等时,检流计中无电流通过,电桥达到了平衡,这时有:R2/R1=Rx/R3,即*Rx=(R2/R1)R3。若 R1.R2.R3 均已知,则 Rx 可由上式求出。
电桥电路可以这样理解,电源 E.R2.Rx 是一个分压电路,Rx 上的电压为[Rx/(R1+R2)]?E,又 E 和 R1.R3 也是 一个 分压电路,R3 上的电压等于[R3/(R3+R1)]?E,现在用检流计来比较 Rx 和 R3 的电压,根据电流方向,可 以发现哪一 个电压更大些。当检流计指零时,说明两电压相等,也就得出*式。
三、实验仪器:
线式电桥板、电阻箱、滑线变阻器、检流计、箱式惠斯通电桥、待测电阻、低压直流电源。
四、实验内容和步骤:
1、标准电阻 Rn 选择开关选择“单桥”档;
2、工作方式开关选择“单桥”档;
3、电源选择开关选在有效量程里;
4、G 开关选择“G 内接”;
5、根据 Rx 的估计值,选好量成倍率,设置好 R1R2 值和 R3 值,将位值电阻 Rx 接入 Rx 接线端子(注意 Rx 端于上 方短接片应接好); 6、打开仪器市电开关、面板指示灯亮;
7、建议选择毫伏表作为仪器检流计,释放“接入”键,量程置“2mV”挡,调节“调零”电位器,将数显表调零。 调零后将量程转入 200mV 量程,按下“接入”按键,也可以选择微安表做检流计;
8、调节 R3 各盘电阻,粗平衡后,可以选择 20mV 或 2mV 挡,细调 R3,使电桥平衡;
9、按下式计算被测电阻值: Rx=(R2/R1)R3
五、实验数据与处理:
六、误差分析:
1.检流计灵敏度可导致偶然误差增大
2.导线电阻可使测量值偏大或偏小,跟电路中电阻分布有关,属系统误差
3.待测电阻两端接触电阻均可造成测量结果偏大
4.实验中周围的电子设备干扰
5.电阻随温度变化有所改变
6.选择的和过小造成系统误差,增大灵敏度 RR12
七、思考题:
1.Rx=(R3/R2)R1
2.两种,一种是固定 R3,调整 R1 与 R2 的比值。另一种是固定 R1 与 R2 的比值,调整 R3,。一般采用后一种。 3.为了电路安全。调小是为了使实验数据明显。防止短路。
4. 按照线路图检查所使用的电桥,并进行检验。线路接上电源后,从比例臂 R1 和 R2 上取下 10Ω上的插塞,并把比 较臂 R3 的无穷大插塞取下,瞬时地先后合上电源开关和检流计开关,记录检流计的偏转方向;把 R3 的无穷大插 塞 插 R 原处后重复上。述实验操作,如果检流计的偏转与上次相反,就说明线路的连接无误。按一定顺序在 R3 上取下 插塞,用上述方法把按键开关接通,在检流计不发生偏转时,读取 R3 的值。若取 R1,R2,则比率 R1, R2 为 1:1, 这时测得的 R3 的值将比在其它比率下更加接近未知电阻 R4。在 R1,R2 的其它比率下测定 R4 的 值后,确定每次测 量的误差。
八(注意事项;
1.用线式电桥测电阻时,电源电压取 3~5V,电压太小灵敏度得不到保障,电压太大容易损坏仪器。
2.Rp 在实验前应置于阻值最大位置,减小 Rp 后应尽快测量,然后增大 Rp 或切断电源,否则由于电流过大容 易引起电阻丝发热,烧坏标尺或电阻箱。
3. 箱式电桥应轻拿轻放,旋动表弹簧旋钮时应轻轻操作,切忌过 猛,否则容易损坏检流计。 4.严禁在没有确定好比例臂和 R3 值较小或者为零的情况按下 G0 开关。
九、附上原始数据:
范文五:惠斯通电桥实验报告.pdf
南昌 大学物 理实 验报告
课程名称:
惠斯通电桥 实验名称: 惠斯通电桥 学院: 眼视光学院 专业班级: 眼视光 151 班 学生姓名: 许春芸 学号: 6303615024 实验地点: 210 座位号: 30 座
实验时间: 第8周星期 6 上午10点10开始
一、实验目的:
1.掌握电桥测电阻的原理和方法。 2.了解减小测电阻误差的一般方法。
二、实验原理:
B 和 D 之间连接检流计 G,所谓桥就是指 BD 这条对角线,它的作用就是将桥的两个端点的电势直接进行比较。 当 B.D 两点 电势相等时,检流计中无电流通过,电桥达到了平衡,这时有:R2/R1=Rx/R3,即*Rx=(R2/R1)R3。若 R1.R2.R3 惠斯通电桥的电路四个电阻 R1.R2.R3.Rx 连成一个四边形,每一条边称作电桥的一个臂,对角 A 和 C 加上电源 E, 对角
均已知,则 Rx 可由上式求出。
电桥电路可以这样理解,电源 E.R2.Rx 是一个分压电路,Rx 上的电压为[Rx/(R1+R2)]·E,又 E 和 R1.R3 也是 一个 分压电路,R3 上的电压等于[R3/(R3+R1)]·E,现在用检流计来比较 Rx 和 R3 的电压,根据电流方向,可 以发现哪一 个电压更大些。当检流计指零时,说明两电压相等,也就得出*式。
三、实验仪器:
线式电桥板、电阻箱、滑线变阻器、检流计、箱式惠斯通电桥、待测电阻、低压直流电源。
四、实验内容和步骤:
1、标准电阻 Rn 选择开关选择“单桥”档; 2、工作方式开关选择“单桥”档; 3、电源选择开关选在有效量程里; 4、G 开关选择“G 内接”;
5、根据 Rx 的估计值,选好量成倍率,设置好 R1R2 值和 R3 值,将位值电阻 Rx 接入 Rx 接线端子(注意 Rx 端于上 方短接片应接好); 6、打开仪器市电开关、面板指示灯亮;
7、建议选择毫伏表作为仪器检流计,释放“接入”键,量程置“2mV”挡,调节“调零”电位器,将数显表调零。 调零后将量程转入 200mV 量程,按下“接入”按键,也可以选择微安表做检流计;
8、调节 R3 各盘电阻,粗平衡后,可以选择 20mV 或 2mV 挡,细调 R3,使电桥平衡;
9、按下式计算被测电阻值: Rx=(R2/R1)R3
五、实验数据与处理:
六、误差分析:
1.检流计灵敏度可导致偶然误差增大
2.导线电阻可使测量值偏大或偏小,跟电路中电阻分布有关,属系统误差
3.待测电阻两端接触电阻均可造成测量结果偏大
4.实验中周围的电子设备干扰
5.电阻随温度变化有所改变
6.选择的R1和R2过小造成系统误差,增大灵敏度
七、思考题: 1.Rx=(R3/R2)R1
2.两种,一种是固定 R3,调整 R1 与 R2 的比值。另一种是固定 R1 与 R2 的比值,调整 R3,。一般采用后一种。 3.为了电路安全。调小是为了使实验数据明显。防止短路。 4. 按照线路图检查所使用的电桥,并进行检验。线路接上电源后,从比例臂 R1 和 R2 上取下 10Ω上的插塞,并把比 较臂 R3 的无穷大插塞取下,瞬时地先后合上电源开关和检流计开关,记录检流计的偏转方向;把 R3 的无穷大插 塞 插 R 原处后重复上。述实验操作,如果检流计的偏转与上次相反,就说明线路的连接无误。按一定顺序在 R3 上取下 插塞,用上述方法把按键开关接通,在检流计不发生偏转时,读取 R3 的值。若取 R1=R2,则比率 R1/ R2 为 1:1, 这时测得的 R3 的值将比在其它比率下更加接近未知电阻 R4。在 R1/R2 的其它比率下测定 R4 的 值后,确定每次测 量的误差。
八.注意事项;
1.用线式电桥测电阻时,电源电压取 3~5V,电压太小灵敏度得不到保障,电压太大容易损坏仪器。
2.Rp 在实验前应置于阻值最大位置,减小 Rp 后应尽快测量,然后增大 Rp 或切断电源,否则由于电流过大容 易引起电阻丝发热,烧坏标尺或电阻箱。
3. 箱式电桥应轻拿轻放,旋动表弹簧旋钮时应轻轻操作,切忌过 猛,否则容易损坏检流计。
4.严禁在没有确定好比例臂和 R3 值较小或者为零的情况按下 G0 开关。
九、附上原始数据: