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  1. #1
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    Unsure about this current sensor for use in saturation current measuring circuit.

    Hello.

    I acquired a sensor called S25P050D15X with the intention to use it in a circuit to measure the saturation current of ferromagnetic cores i.e. inductors and transformers, but my concern is this, the sensors datasheet can be found here.
    Further down on page 2(the last page) there is this warning:
    CAUTION
    Do not wrap the primary conductor around the core part of the product to increase measured current.

    The thing is that I was relying on doing just that in order to make use of this sensor as it is rated for 50A and I will rarely if ever measure 50A, mostly I will probably measure below 5A but I wanted to be able to measure up to 50A while being able to measure much lower currents with a larger output response from the sensor by looping the primary multiple times through the core. Does anyone have any suggestions or insights into why this is prohibited?

    I wonder if this restriction has something to do with the fact that this sensor is of the "closed loop type" as opposed to the "open loop type", as I am writing this that seems as a very plausible explanation.

    The circuit that this sensor would be used in is often used to read the result directly on an oscilloscope but I was hopping to in the end enable a microcontroller to record the measurements and by some algorithm hopefully mostly be able to detect the knee in the waveform where the core saturates and the current as a result increases(and then display that value on a display of some sort). In ether case one solution might simply be to amplify the sensors output voltage to make it more discernable on the scope or the the µC's algorithm.

    First I thought "what if I simply increase the output resistor to create a larger voltage across said resistor" but the datasheet states that the:
    Measuring resistance =
    60Ω~95Ω (at VCC= ±12V)
    135Ω~ 155Ω (at VCC = ±15V)

    So amplifying the voltage is perhaps the way to go, I was recommended to just buy a cheap sensor on ebay but oh no I wanted to buy a more expensive sensor to make more accurate measurements... I should have gone with a open loop type sensor.

    By the way, the attached circuit was posted by the member Warpspeed in a old thread I had in which he suggested that circuit instead of the usual single low-side switch + capacitor bank that you see all over the internet, I like the circuit Warpspeed suggested much more.

    Any and all thoughts about this is very welcome.

    Regards

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  2. #2
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    Re: Unsure about this current sensor for use in saturation current measuring circuit.

    I think the "don't wrap it twice" issue is more about protecting the hall effect device and the circuits that go with it.
    note the output saturates at +/-8V if the current tops about 55 A.

    it is generally best to follow the manufacturer's data sheet and the restrictions therein to have long lasting, working components.

    if you build the current monitor circuit with one pass through the center, is the output sufficient and useable?
    what is the observed saturation current? (average and standard deviation for at least 9 measurements?)

    putting the wire through a second time will double the observed current and will make the current sensor into an inductor
    instead of a transformer - can you guarantee the device to NOT get saturated, or overworked, or ...?



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    Re: Unsure about this current sensor for use in saturation current measuring circuit.

    Hi,

    It seems you don't need isolation.
    If so, then - in my eyes - the best method to measure currents in tge given range is a shunt ... added with a suitable amplifier.
    There are even dedicated "current sense amplifiers".
    They give good frequency response, good linearity, and good precision.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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  4. #4
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    Re: Unsure about this current sensor for use in saturation current measuring circuit.

    tight looping of cable will no doubt affect the accuracy - if you can have large diameter looping, say 300mm then such effects will be minimised



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    Re: Unsure about this current sensor for use in saturation current measuring circuit.

    The warning is in the UL compliance section and obviously related to sensor temperature rise. Probably no problem in your application.

    The other point has been addressed by Easy peasy. The sensor is calibrated for straight single conductor. Depending on the core shape, permeability and hall sensor position, a multi-turn primary may affect the accuracy. A tightly wound multi-turn can be still reasonable.



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