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PGA900: overcurrent from chip used in Milone water level sensor

Jackson Miller
Prodigy 10 points
Part Number: PGA900

I am using a system manufactured by Milone Technology that uses the PGA900 chip to provide a 4-20 mA output I am powering it with 12V and after a few days the system is outputting closer to 40 mA

The company is milone technologies, here is a link to their datasheet: https://img1.wsimg.com/blobby/go/6e1bce17-f4fa-40c3-9d89-9bb7445697bb/downloads/4-20mA%20Module%20Data%20Sheet.pdf

The problem is that after powering the system for about 5 days with 12V it suddenly begins to output close to 40 mA. I see a 5V drop over my 120Ohm resistor connected in line to the 4-20mA signal The maximum should be ~2.4V drop over the resistor

 I am wondering to cause an overcurrent situation if there is a particular component in the chip such as a mosfet that would fail. This will help me with troubleshooting.

Thanks!

  • 0
    TI__Mastermind 31655 points

    Hi Jackson,

    It is tough to say without understanding the firmware that Milone uses. It's possible that they have tied the internal diagnostics of the PGA900 to a DAC output that is outside of the normal 4-20mA output range. So a particular diagnostic flag may cause an output of 40mA. I would check if they have any documentation on this. 

    Does the output return to normal if the power to the device is reset? And does it begin outputting 40mA again after a while? Does the output creep up to 40mA, or does it instantly jump?

    Again, it is difficult to comment on the system because a lot depends on the firmware, so I would recommend contacting Milone as well.

    Regards,

    Scott

  • 0 in reply to Scott Cummins
    Prodigy 10 points

    Hi Scott,

    Thank you for your reply.  To answer your questions:

    - I have reached out to Milone and they have not yet sent me documentation on diagnostic behaviors that would output 40 mA

    - The current increase happens within a 5 minute period and does not appear to be gradual

    - After the instrument begins outputting 40 mA if power is cut to the system and it is restarted after a brief 2 minute pause, it continues to output 40mA immediately. I have taken the Milone sensors out of the field once they begin exhibiting this behavior. Installing a new one in its place has resolved the issue so far in the systems where this has happened however there is nothing stopping it from happening again.

    - Our appliance uses an AC to DC converter to output the 12V, I am wondering if DC ripple from the converter could be causing this issue, however I do not have any way to measure that.

    Thank you,

    Jackson