Im working on a AC triac motor controller for universal motors For this I want to measure the motor current and the speed. For the speed the motor provides a tacho-signal. To isolate the measurement I will use a current sense transformer for the motor current before feeding the signal to the ADC. But what I am not sure about is wether an isolation of the tachometer signals are necessary. I do not have any documentation of the motor but i guess it uses a hall sensor for providing the tacho signal. So in my opinion no isolation is needed and I can feed the signal directly to the ADC but I want to make sure I am right.

So my question is:

What is your opinion? Do I need an Isolation for the tacho signals?

thanks in advance

  • \$\begingroup\$ Whatever type of tacho it is, it is most likely isolated. You need to shield the cable for it and keep it away from power cables. However, there is no way for anyone to know exactly what you have, so any answer must be a mater of opinion as your question indicated. Such questions are "off topic" here. I am voting to close the question. \$\endgroup\$ – Charles Cowie Jul 28 '19 at 12:51
  • \$\begingroup\$ Could you do more to investigate if the tacho is isolated? measure the impedance from it to the motor teminals + case? find a data sheet for the motor? have a look inside? \$\endgroup\$ – Will Jul 28 '19 at 12:58
  • \$\begingroup\$ You are asking people to speculate about what you have, and that is not the purpose of this site. At present you're not even sure if you have a pulse type encoder output or an actual tachometer winding. Don't forget that your TRIAC drive presents isolation challenges, too. \$\endgroup\$ – Chris Stratton Jul 28 '19 at 14:01
  • \$\begingroup\$ I am not speculating. I do not have the motor at the moment so I can not do any measurements for verification. But, I know there are no information printed on the motor. So I have made an assumption and asked here because universal motors especially from washing machines are often used by many people. So it ist not unlikely that some people already have some experience with the tacho-signals. Regarding the TRIAC: It is isolated by an Optotriac from AC mains \$\endgroup\$ – S.G Jul 28 '19 at 14:16

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