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Recording Current \ Voltage

Other Parts Discussed in Thread: INA199, INA3221, INA233, INA226, INA220, INA219, INA199EVM, INA226EVM

I have a PCB with 0603 series jumpers on each power line. I would like to find a component that I can solder onto this jumper that can be used with some sort of device that can hook into my computer to measure \ record the current \ voltage. Currently I use an a wire with a current probe and oscilloscope but I need to make more accurate recordings. Do any of you know of something I could use ?

  • Hello Shmuel,

    There is no simple one-IC answer to your inquiry.  You would have to design a sub-system to measure and provide the digitized measurements.  I suggest you start here: https://e2e.ti.com/blogs_/b/msp430blog/archive/2018/11/06/accelerate-your-metering-design-with-the-new-energy-measurement-design-center-and-software-library-for-msp430-mcus .  There is a block diagram that shows what you would have to design for this task.  Or perhaps you could purchase a DVM with a USB interface.

    Regards,

    ~Leonard

     

  • Dear Leonard,

    Thank you for your response. I looked at what you sent me but this looks like for a higher voltage \ current design.

    I am looking at max 1.1V - 5V at max of 3-6A. I was thinking of something like a current Sense amplifier like the TI INA199 or similar ? I think I would need a shunt resistor and some sort of development board ?

    Best regards

    Shmuel 

  • Hi Shmuel,

    Yes, an INA device could be used, then you would need an ADC, plus communications, plus isolation.  Here is a Ref Design that uses the AMC1304, includes an MSP430, and is isolated: http://www.ti.com/tool/TIDA-01094 . 

    See if this would be closer to your needs.

    ~Leonard 

     

  • Dear Leonard,

    Since it looks like an INA device will fit my needs, what I am really looking for is a development board \ module with an INA chip which I can use to make my measurements with my shunt resistor on my PCB. Does TI have something like this ?

    Regards

    Shmuel

  • Hello Shmuel,

    Actually we do have an evaluation module (EVM) for the INA199 here.  For future reference, if you go to any device product page and click the "Tools and Software" tab, you will be able to see any EVM or TI-designs that are available for that device.  

    As you want to read the measurement on the computer, this could be a bit of a challenge, as the INA199EVM output is analog.  Without a Microcontroller or ADC, that likely only leaves you with an audio jack as an input option and that will require you some creativity to satisfy the pc audio jack requirements.  So I would recommend using an ADC or microcontroller EVM to interface between the INA199 and your computer.  Alternatively, you could try one of our power monitor devices: INA219, INA220, INA226, INA233, or INA3221.  These have an I2C interface.  With the EVM to one of the aforementioned devices, you could pair it with one of these USB to I2C evaluation modules I found on digikey(https://www.digikey.com/products/en/development-boards-kits-programmers/evaluation-and-demonstration-boards-and-kits/787?FV=ffe00313&quantity=0&ColumnSort=1000011&page=1&k=usb+to+i2c&pageSize=500)

  • Dear Patrick,

    The power monitor devices sound good - I will need a high-side sensing EVM ! 

    Does TI have any EVM that connect via USB directly to the PC ?

    Alternatively We have a TI EV2300 - will this do the job ?

    Regards

    Shmuel 

  • Hey Shmuel,

    Glad you asked!  I actually absent-mindedly forgot that several of our power monitor devices are outfitted such that they can be monitored on the computer with a GUI we developed.  Below is a picture I took from the INA226EVM user manual confirming this.  All of the items below should be included in the kit, if you decide to purchase it.

    As for the EV2300, I am not super familiar with it.  However, If you want to proceed with that one, I can forward this question to someone in the responsible product line that can help.

  • Dear Patrick,

    I looked at the data sheet for the  INA226EVM and it looks like exactly what I am looking for - thank you ! 

    I have series resistors 0 Ohm 0603 on my power rails on my PCB I assume that the  INA226EVM can be used with a SMD 0603 Shunt resistor ? Is there any specific resistor that is recommended ?

    Regards

    Shmuel 

  • Also what are the measurement going to be like(aren't there going to be significant deviations for the real measurements) since we will have to use wires to connect from the PCB Shunt resistor to the EVM (in the data sheet they show what looks like the shunt resistor directly connected to the EVM (very short connection) ??
  • Hello Shmuel,

    0603 is fine.  However, if you needed really high precision, you may consider a 4-terminal kelvin connect resistor like shown below.  But for that precision, it will cost you. Depending on the resistor value, those kelvin connect resistors can be greater than $10 per part.  As for the shunt, the wires should not create too large of error in your measurement as long as the resistance from your sense resistor to the INA226 input pin is only a few ohms.  One thing you might consider if you do not need an input filter for your tests, would be to place your shunt at the C1 spot on the EVM board.

  • Dear Patrick,

    Thanks for your reply.

    So what value SHunt resistor would you recommend and what % precision ? 

    Also what thickness \ gauge(remember it can't be too thick or we will not be able to solder it onto the pads of the 0603 Shunt resistor on our PCB) and MAX length of the wire would you recommend 

    Sorry I didn't understand what you meant by putting the Shunt resistor on the position of the C1 spot - our Shunt is to be installed on our own PCB product not the EVM ???

    Best regards

    Shmuel

  • Hello Shmuel,

    The % precision or % error you can tolerate depends on your control system.  We recommend 10% worst case, but you can certainly strive for better than that.  The lower bound of the range is where the percent error is the worst without performing any calibration.  This is due to the device input offset voltage.  For a quick estimate of your worst % error you can calculate Vos(Max)/(I_min*Rshunt)*100.  Your rshunt value would be determined by 81.92mV/I_max (assuming you want to measure the full range, if not you can choose a smaller current to focus on the smaller current range and have greater resolution).

    As for connecting your system, I presume you want to do something like in the top figure, while what I am proposing is in the bottom figure.  I think either will get you to your objective.  As for the gauge, I would get whatever gauge is rated for your current.  Here is online calculator.  This calculator also accounts for length. There are also several wire gauge/current rating charts you can pullup with whatever search engine you prefer.