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WEBENCH® Tools/DRV425: Urgent: DRV 425 Measurement of current without electrical connection

Part Number: DRV425
Other Parts Discussed in Thread: TIDA-01467

Tool/software: WEBENCH® Design Tools

Dear Sir,

We are working on motor monitoring .and we want to know about the signature analysis of the motor for the monitoring. I was looking for some sensor-related to it. But the problem I am facing is all the sensors is they need an electrical connection for the motor to know its current and voltage.

Below is the list of some design guide 

Drv425 can tell the current using the magnetic field but we are not going to drive the motor with motor driver PCB. We will use the drive for the AC motor and the electrical connection for the motor will in panel only.no wiring be there after that.so we will be having a wireless module on the AC motor on the field which will measure the current in the field only.

  • Hello Divyanshu,

    The only design guide that uses the DRV425 is http://www.ti.com/tool/TIDA-01467.  This is because all the other use a magnetic core and a magnetic feedback in order to measure the current.  They do not use the electrical connection as they are using the magnetic field to capture the current measurement.  The DRV425 is only a flux-gate magnetic sensor so if you are attempting to measure only current then you will be required to use a simulation tool (FEMM , Maxwell from ANSY) or calculations to the the magnetic field from current at a given distance.  Please be aware that there will be many errors that you could come across.  One is stray fields, and another is mechanical placement.  TIDA-01467 uses a differenetial method to avoid stay fields but will still have errors due to mechanical limitation of the PCB.  We show this differential approach with the http://www.ti.com/tool/DRV425-BUSBAR-EVM design guide and this document explains how it works http://www.ti.com/lit/an/sloa237/sloa237.pdf.

    If you are not using the flux gate to measure current but rather the health of the motor I would recommend looking at this paper.

    https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7590101

  • Dear Sir,

    Thanks for your input. Below is the picture that helps you to know the actual application.
    We want to measure the signature analysis for the AC motor but in filed we cannot put any electrical connection so it is feasible that DRV425 can give exact current sensing of the magnetic field.?

    Distance will be more even accuracy will not be high but still, DRV425 is good to choose.?Or anything TI can suggest for Current and voltage measurement wirelessly.

    If not which would be the best way to know this type of monitoring.?

  • This box will be the device to measure current which will be wirelessly no connection on the field.

  • Hello Divyanshu,

    The DRV425 can measure the magnetic field but getting it accurately represent the current will take need much into account and calibrated.  As each phase will generate a field and will impact each sensing element.  The easiest way is to have an individual core with the current running through it.  If it is AC a current transformer may work or the other applications with a magnetic core.  The magnetic core concentrates the field you are interested in while rejecting the signals you do not want.  The DRV425 may be less power but if will also require more mechanical issues as you will get stray fields from each phase and from the motor itself.  The motor does shield most of the field through its case but there will be some flux leakage.

    When you mention accurate then I would go with the devices with a core and run the current through that.  To get signature the DRV425 can get you that but spacing of the current carrying conductors matter.  Also the DRV425 max filed is limited to 2mT so you will be limited on the distance you can be to measure the current.

    To design the magnetics of this will take some time and effort if you are designing your core.  If you are doing the DRV425 approach I would believe the simulations can be done in FEMM but you will have the errors from the motor field leakage. 

  • Dear Sir,

    Thanks for your input.

    Apart from DRv425 will u suggest something else for this.?

  • Hello Divyanshu,

    I don't have an easy solution for you.  I really would recommend the core versions.