• AVR Freaks

Hot!Load Side Accumulation with PAC1934

Author
dave.williams
New Member
  • Total Posts : 5
  • Reward points : 0
  • Joined: 2011/11/18 08:41:15
  • Location: 0
  • Status: offline
2020/04/28 12:25:08 (permalink)
0

Load Side Accumulation with PAC1934

Reading through the PAC193x documentation, the power measurement is taken from Vbus measured at Isense+ and from Vsense. This gives an accurate reading for power taken from the source, but will cause an offset if you want to measure power delivered to the load.
 
I am guessing the answer is that I'm out of luck, but is there a way to correct for this and accumulate load power [(Vbus-Vsense)*Vsense] or an equivalent part that uses load voltage rather than bus voltage?
 
Thanks
#1

4 Replies Related Threads

    mbrowning
    USNA79
    • Total Posts : 1791
    • Reward points : 0
    • Joined: 2005/03/16 14:32:56
    • Location: Melbourne, FL
    • Status: offline
    Re: Load Side Accumulation with PAC1934 2020/04/28 16:34:39 (permalink)
    0
    I don’t think so but these parts have 16b ADCs if I recall so you don’t need a big sense resistor. I use 0.0005 and 0.002 ohm depending on current. The power wasted in the sense resistor shouldn’t be higher than then inherent inaccuracy of the resistor and sensor. If so you are using too big a resistor.

    That said, you know the resistor value and you can read average current so just subtract resistor power from accumulated power.
    #2
    Bob White
    Super Member
    • Total Posts : 336
    • Reward points : 0
    • Joined: 2010/11/06 19:52:38
    • Location: Denver, Colorado
    • Status: offline
    Re: Load Side Accumulation with PAC1934 2020/04/28 18:01:57 (permalink)
    0
     
    Are you worried about losses in wires/traces between the Vsensen- terminals and the terminals at the load?  Otherwise I am not sure I understand your concern.
     
    #3
    mbrowning
    USNA79
    • Total Posts : 1791
    • Reward points : 0
    • Joined: 2005/03/16 14:32:56
    • Location: Melbourne, FL
    • Status: offline
    Re: Load Side Accumulation with PAC1934 2020/04/28 20:16:29 (permalink)
    0
    The "concern" is that power is "upstream" voltage (Vbus in the datasheet, or the voltage at SENSE+) times Vsense (Vsense+ - Vsense-) So power includes both load power and sense resistor wasted power. I think with good sense resistor selection the sense resistor power is negligible.
     
    However, I just remembered a way to measure power not including sense resistor dissipation. Current measurement can be (and power always is) bidirectional (2's comp). Just connect the sense lines backwards so that source is on SENSE- and load is on SENSE+. You set operation to bi-directional, and now you are measuring load voltage and power. Current and power are negative, so invert and be happy.
    #4
    dave.williams
    New Member
    • Total Posts : 5
    • Reward points : 0
    • Joined: 2011/11/18 08:41:15
    • Location: 0
    • Status: offline
    Re: Load Side Accumulation with PAC1934 2020/04/29 07:25:05 (permalink)
    0
    That's an excellent solution, I will give that a try.
    I am looking at logging some wireless sensors which can provide challenges with a very wide current range at low voltage, from ~50mA while transmitting down into the microamp range while in sleep. I'm leaning at going with a 1Ω sense resistor to give a 1.5µA LSB, but while dropping 50mV across the sense at 3V isn't the end of the world, it'd be nice to eliminate the extra source of error.
     
    Thanks
    #5
    Jump to:
    © 2020 APG vNext Commercial Version 4.5