故障查找

1、疑似模拟量输出板卡问题，用万用表测量4-20mA输出信号，信号是正常的!

2、开始怀疑是变频器控制信号输入端有了问题，换了一台同型号变频器，问题仍然如此。

3、用一台手持式信号发射器做4-20mA输出信号源，输出标准电流信号至变频器，这下变频器启动了，因而我们排除了模拟量输出板卡和变频器的故障。

4、由此推测是变频器的干扰信号传导至模拟量通道所致。

5、为了验证，在PLC模拟量4-20mA输出通道中加装了一台信号隔离模块TA3012，TA3012的输入端子5、6接模拟量输出模块，输出端子1、2端子接变频器，3、4端子接外部24VDC供电电源，变频器正常启动了。

6、据此断定，问题的根源在于变频器干扰模拟量通道所致。

Fault finding

1. Suspected analog output board issue, measure the 4-20mA output signal with a multimeter, and the signal is normal!

2. I began to suspect that there was a problem with the control signal input of the frequency converter. I replaced it with a frequency converter of the same model, but the problem still persists.

3. We used a handheld signal transmitter as a 4-20mA output signal source, outputting a standard current signal to the frequency converter. As a result, the frequency converter started, and we ruled out faults with the analog output board and frequency converter.

4. It can be inferred that the interference signal from the frequency converter is transmitted to the analog channel.

5. To verify, a signal isolation module TA3012 was installed in the 4-20mA output channel of the PLC analog signal. Input terminals 5 and 6 of TA3012 were connected to the analog output module, output terminals 1 and 2 were connected to the frequency converter, and terminals 3 and 4 were connected to an external 24VDC power supply. The frequency converter started normally.

6. Based on this, it can be concluded that the root cause of the problem lies in the interference of the frequency converter with the analog channel.