4-20mA输出的仪表显示20mA，为什么测出来是不一样
<p style="text-align:center"><img src="/public/uploads/images/20260331/1774937630104549.jpg" title="1774937630104549.jpg" alt="96db14b33be3be39d6f76c5487ef6590_compress.jpg"/></p><p> 今天我们来介绍一下导致仪表电流显示值与测量值不相同的原因。</p><p>一、常见原因</p><p> 1、正负极接反</p><p> 两线制 4-20mA 变送器正负极接反时，有些仪表会直接输出20mA值来保护仪表，也有一些仪表会输出一个负的电流。这种情况比较容易发现。</p><p> 2、量程设置</p><p> 4-20mA对应上下限设置反了，测量值为0的时候应该输出4-20，设置反了之后则会输错20mA。</p><p> 3、传感器故障</p><p> 也有可能是一个传感器出现故障导致变送器输出满量程故障信号，压力、液位计、温度都可能会出现这种情况。</p><p> 4、PLC设置问题</p><p> 问题也可能出现在PLC端，可能是量程设置错误，如0-20mA，也也可以是上下限写反。这些都是比较容易可以查出的原因。 </p><h2 style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; font-family: ui-sans-serif, system-ui, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji"; font-size: 16px; font-weight: 400; line-height: 24px; text-wrap-mode: wrap; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;">二、常见中等概率故障诱因</h2><p>1、回路短路<br/></p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;"> 线缆外皮破损渗水、接线端子受潮氧化，极易造成信号正负极搭接短路；多数工业仪表具备短路自检功能，一旦识别回路异常，会直接锁定输出满量程 20mA 报警状态。</p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;">2、供电不稳与信号干扰</p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;"> 现场 24V 直流供电电压波动、线路压降超标，或是接地不当产生环流干扰，都会打乱仪表正常运算逻辑；设备判定工况异常后，会触发保护机制，强制输出 20mA 故障信号。</p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;">3、仪表保护模式</p><div style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;"> 传感器故障、探头断线、内部模块异常时，仪表会启动出厂故障兜底设定：常规默认满量程 20mA 上限输出，以此提醒运维人员排查设备本体问题。</div><h2 style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; font-family: ui-sans-serif, system-ui, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji"; font-size: 16px; font-weight: 400; line-height: 24px; text-wrap-mode: wrap; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;">三、快速排查实操步骤（简易高效）</h2><p>1、单独测电流<br/></p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;"> 断开仪表与后端线路的接线，单独测量仪表输出电流：若依旧固定 20mA，判定为仪表硬件损坏、接线极性错误或参数设置异常；若电流回落至正常 4mA 基准值，说明故障源于外接线路短路、DCS 模块配置错误。</p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;">2、调换正负极</p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;"> 互换两根信号线的接线位置，若电流立马恢复正常数值，可直接确定是前期正负极接反导致的异常。</p><p style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;">3、查看故障</p><div style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; line-height: 24px; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;"> 进入仪表参数界面，若屏幕弹出 OL、超限、故障代码等标识，代表传感器或内部机芯已损坏；若本机测量数值显示正常，但对外仍输出 20mA，大概率是故障输出逻辑、量程参数配置出错。</div><h2 style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; font-family: ui-sans-serif, system-ui, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji"; font-size: 16px; font-weight: 400; line-height: 24px; text-wrap-mode: wrap; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;">四、核心问题总结</h2><div style="font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-alternates: normal; font-size-adjust: none; font-language-override: normal; font-kerning: auto; font-optical-sizing: auto; font-feature-settings: normal; font-variation-settings: normal; font-variant-position: normal; font-variant-emoji: normal; font-stretch: normal; font-family: ui-sans-serif, system-ui, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji"; line-height: 24px; text-wrap-mode: wrap; flex: 0 1 auto; flex-direction: row; justify-content: normal; align-items: normal; padding: 0px; margin: 0px; background-image: none; background-position: 0% 0%; background-size: auto; background-repeat: repeat; background-attachment: scroll; background-origin: padding-box; background-clip: border-box;"> 实际工况无数据、仪表却恒定输出 20mA，归根结底只有三类原因：一是信号线正负极接线颠倒；二是量程标定、故障输出等参数设置反向；三是传感器本体损坏，或是外部信号线路存在短路问题。</div><p> 想要了解更多可以添加下方微信进行咨询也可以加入仪器仪表交流群一起交流，或是拨打153 2371 3323 公众号、官网http://ainstru.com/也有更多内容可以查看。</p><p style="text-align:center"><img src="/public/uploads/images/20260331/1774939043581589.png" title="1774939043581589.png" alt="微信图片_2025-12-19_171133_163.png" width="155" height="154"/></p><p><br/></p>