一次令人捉摸不透的维修 | 变频器有正转信号，但频率始终为零，怎么办？
|转至：电力合伙人
变频器上电后，启动变频器，使能正转端子与公共端接通！变频器RUN灯亮起！用户多次通过 人机界面给变频器运行频率后，变频器无反应，且频率始终为零！
变频器的频率已设定由外部端子给定，这台变频器是控制牵引机电机的，因为本厂是生产管道的，需要有电机牵引管子生产！变频器和电机的组合我们称它为牵引机！变频器就是来驱动这两台电机。
变频器的频率是用户通过人机界面写入PLC（本PLC为西门子S7——200）；
然后由PLC给频率给变频器！人机界面上的牵引速度，设定，就是说的给这台变频器的频率！
当用户将需要的速度通过人机界面写入到PLC后，然后由PLC的扩展模块EM232（模拟量输出模块），输出一个0V到10V的电压，给我们的变频器实现频率设定！EM232模块图片）
EM232模块是模拟量输出模块！端子上标有M0,V0,I0,M1,V1,I1,这就是模拟量输出的接线端子，如果你要的输出是电压信号，就接M0，V0，和M1，V1，电流信号就接M0，I0，和M1，I1。M为公共端，V表示电压，I表示电流，后面的0,1表示通道号。
变频器端子（AI1）AI是Analog input 模拟量输入的缩写，1表示通道1！那么EM232模块与变频器是怎么连接的呢？我给大家画出了电路图。
EM232模块根据用户设定的速度，它的端子M0，V0，会输出一个0V到10V的电压，传递到变频器模拟量输入端子GND，AI1，变频器就是通过获取GND，AI1，端子上的电压来改变频率和设定频率！
现在已经给大家讲清楚了这台设备的工作原理，那么我们现在来处理这个故障！
在人机界面设定好速度后，我用万用表测量变频器端子，GND，AI1，是否有直流电压。经测量万用表显示为为零，无电压！刚开始心想可能是端子（EM232模块）M0到（变频器端子）GND和（EM232模块）V0到（变频器端子）AI1的线断了，导致无电压！
为了排除线断的可能，在人机界面设定好速度后，我用万用表测量EM232模块端子M0和V0是否有电压输出！结果测得电压为0V，这也排除了线断的可能！（由于当时拍照灯光问题看不清楚，只能给大家模拟一下）
既然线路没有问题，那我就怀疑是这个EM232模拟量输出模块坏了，我就把这个模块拆下来。然后从别的机台拆了一个完好的EM232模块，给它装上去！装上去后试机，测得变频器端子GND，AI1，有电压！证明EM232模块有电压输出！此时变频器上有频率且牵引电机已经转起来了！
更换EM232模块后，故障排除，设备运行正常！造成此次设备故障的主要原因是由于EM232模块损坏，无电压输出！
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