3.2 电位器的参数与标识
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3.2.1 电位器的命名
国产电位器的型号主要由四部分组成,如图3-9所示:
第1部分为电位器的组成部分,用字母W表示电位器的名字。
第2部分为导电材料部分,用字母表示电阻体是由什么材料组成,如图,如表3-4所示为电阻体材料符号和意义。
表3-4 电阻体材料符号和意义
|
符号 |
材料 |
符号 |
材料 |
D |
导电材料 |
N |
无机实心 |
F |
复合膜 |
S |
有机实心 |
H |
合成碳膜 |
X |
线绕 |
I |
玻璃轴膜 |
Y |
氧化膜 |
J |
金属膜 |
|
|
第3部分为电位器的类别,一般用字母表示,如表3-5所示为电位器类别、符号和意义。
|
|
|
|
符号 |
类别 |
符号 |
类别 |
B |
片式类 |
P |
旋转功率类 |
D |
多圈旋转精密类 |
T |
特殊类 |
H |
组合类 |
W |
螺杆驱动预调类 |
G |
高压类 |
X |
旋转低功率类 |
J |
单圈旋转精密类 |
Y |
旋转预调类 |
M |
直滑式类 |
Z |
直滑式低功率类 |
第4部分为电位器的序号,用数字表示同类产品中不同品种,以区分产品的外形尺寸和性能指标等。
例如,WHX-1 470kΩ,表示旋转低功率合成碳膜电位器,阻值为470kΩ,W表示电位器,H表示合成碳膜,X表示旋转低功率,-1为序号,470kΩ为阻值。
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3.2.2 电位器的参数
1. 标称阻值
标称阻值通常是指电位器上标注的电阻值,电阻值的基本单位是欧姆,用Ω表示,在实际应用中还常用千欧(kΩ),和兆欧(MΩ)来表示。
2. 额定功率
电位器的额定功率是指在标准大气压和一定环境温度下,电位器能够长期负荷而不改变其性能所允许的功率,功率用P表示,单位瓦特(W)。
3. 阻值变化规律
阻值变化规律是指电位器旋转角度(或形程),与其作为分压器使用时输出电压的关系。常见电位器的阻值变化规律有线性变化型、指数变化型和对数变化型。
<1> 直线式电位器(用A表示),其电阻体上的导电物质分布均匀,单位长度的阻值大致相等,电阻值的变化与电位器的旋钮角度呈直线关系,多用于分压。
<2> 对数式电位器(用B表示),其电阻体上的导电物质分布不均匀,刚开始转动时阻值的变化较小,转动角度增大时阻值的变化较大,阻值的变化与电位器的旋转角度呈指数关系,多用于音量控制。
<3> 反转对数式电位器(用C表示),其电阻体上的导电物质分布不均匀,刚开始转动时阻值的变化很大,转动角度增大时阻值的变化较小,阻值的变化与电位器的旋转角度呈对数关系,多用于音量控制。
4. 滑动噪声
当电刷在电阻体上滑动时,电位器中心端与固定端之间的电压出现无规律的起伏,这种起伏称为电位器的滑动噪声,它是由材料电阻率分布的不均匀以及电刷滑动使接触电阻的无规律变化引起的。
5. 额定工作电压
额定工作电压是指电位器在规定的条件下,能长期可靠的工作时所允许承受的最高工作电压,电位器的实际工作电压应小于额定电压。
6. 分辨率
分辨率是指电位器的阻值连续变化时,其阻值变化量与输出电压的比值,非线绕电位器的分辨率较线绕电位器的分辨率要高。
7. 动噪声
动噪声是指电位器在外加电压工作下,其动触点在电阻体上滑动时产生的电噪声,该噪声的大小与转轴速度接触点和电阻体之间的接触电阻、动触点的数目、电阻体电阻率的不均匀变化及外加电压大小等有关。
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3.2.3 电位器的标识方法
电位器的标注一般都采用直标法,即用字母和数字直接标注在电位器上。一般标注的内容有电位器的型号、类别、标称阻值和额定功率等。有时电位器还将电位器的输出特性的代号标注出来,其中,Z表示指数,D表示对数,X表示线性。
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