心电图机的功能转换电路通常设计成:功能开关在“准备”或“观察”位置时,控制走纸马达直流继电器(在XDH型心电图机中为J_2继电器)工作,常闭触点打开,走纸马达电路被切断;功能开关在“记录”位置时,继电器不工作,常闭触点闭合,接通走纸马达电路。心电图机使用年代长远后,会使常闭触点烧焊在二起而不能断开。这样,功能开关即使在“准备”或“观察”位置,也会使走纸马送工作。这种故障通常用更换继电器的办法来排除。笔者曾用继电器中未被利用的常开触点来控制 The function conversion circuit of the electrocardiograph is usually designed to: when the function switch is in the “prepare” or “observe” position, the paper feed motor DC relay (J_2 relay in the XDH electrocardiograph machine) is controlled, the normally closed contact is opened, and the paper is fed The motor circuit is cut off; when the function switch is in the “record” position, the relay does not work, the normally closed contact closes, and the paper feed motor circuit is turned on. After the long-term use of the ECG machine, the normally closed contact will be welded in two and cannot be disconnected. In this way, even if the function switch is in the “ready” or “observed” position, it will send the paper to the job. This type of fault is usually eliminated by replacing the relay. I used to control the unused normally open contacts in the relay