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AC Current Sensing

Matt Romney
Prodigy 140 points
Other Parts Discussed in Thread: INA170

In my application, I am using multiple triacs to switch on/off multiple solenoids. The solenoids are supplied by 24VAC. I need to accomplish two things: 1) Detect a fault condition with the solenoid, i.e. a short in the wiring; and 2) detect the presence of a solenoid on a port. The idea is to use a current sensing IC such as the INA170. A microcontroller would monitor the output of the IC. When a triac is activated and a solenoid is attached to the port, the IC would sense an increase in current of say 250mA. If no current is sensed, the MCU would then know that the port is open, no solenoid is attached. In the fault condition, the IC would sense a very large inrush of current and the MCU would shut down the triac.

Is the INA170 the type of part I'm looking for? Again, the solenoid is 24V AC so I'm trying to detect an AC current. Thank you for your help and suggestions.

  • 0
    Guru 22270 points

    Hello Matt,

    An alternative to using a separate IC would be to use a sensing resistor for each solenoid.  A diode would provide rectification of the feedback voltage across the resistor.

    This could then be sent to the MCU ADC input if it has one.  A cap would smooth out the voltage.  Since you are only concerned about an ON condition or Overcurrent, then you wouldn't require a large cap.  There a plenty of examples of this type of circuit on the web.

    Thanks,

  • 0 in reply to Greenja
    Prodigy 140 points

    Greenja,

    Thank you for your quick reply. I will do some research and learning. I'm a microwave guy trying to remember how to do analog. Since only one solenoid is on at a time, I could use just one sensing resistor on the main line, correct?

    Matt

  • 0 in reply to Matt Romney
    Guru 22270 points

    That is correct.  The only problem is you would not know which of the solenoids were shorted without physically going to inspect it.  If this is for a sequential operation, then it wouldn't mater.

    Thanks,