PicoScope 7 Automotive
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Pico-Engine Non-Invasive testing Webinar Q & A
Re: Pico-Engine Non-Invasive testing Webinar Q & A
I have some question about the math channel formula.
WHY is the “sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T)*(1000)”?
I think it should be (sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T))*1000?
The first formula did the multiply with channel C，then plus A and B？
The second formula A+B+C,finally multiply 1000.
But the datas of them are different?How to explain ?
WHY is the “sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T)*(1000)”?
I think it should be (sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T))*1000?
The first formula did the multiply with channel C，then plus A and B？
The second formula A+B+C,finally multiply 1000.
But the datas of them are different?How to explain ?
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Steve Smith
- Pico Staff Member
- Posts: 1593
- Joined: Sun Aug 25, 2013 7:22 am
Re: Pico-Engine Non-Invasive testing Webinar Q & A
Hello Zach and thank you for the post and the great catch on the math’s
You are correct as this all comes down to the location of the brackets and mine are incorrect (thank you)
sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T) most certainly returns the collective RMS current of the 3 phases but the confusion arises with the multiplication by 1000.
Given the 3 phase flex probe and DC current clamps were originally used without the relevant custom probe settings, I have converted the values captured on channels A, B, C & D from voltage into current (probe output 1 mV/A)
Channel A, B, C & D are therefore multiplied by 1000 and converted to amps using the formulas A, B, C & D*1000
This is correct for each channel and should also be applied to the sum of the RMS values calculated in the above math channel.
As you have correctly pointed out, the location of my brackets (for calculating the RMS Current) results in only Channel C being multiplied by 1000 and not Channel A or B (highlighted in bold below)
“sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T)*(1000)”
The correct formula to multiply all phase values by 1000 is:
(sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T))*1000
Alternatively, sqrt(integral((A)^2)/T)*1000+sqrt(integral((B)^2)/T)*1000+sqrt(integral((C)^2)/T)*1000 can be used but the formula increases in size
I have added another math channel for discussion thanks to my colleague Jeff, this time looking at average motor current
Here we use -LowPass((abs(A)+abs(B)+abs(C))*1000*0.333,50)
The "-" is to make it match the negative current draw of the battery (Channel D)
The "LowPass" smooths out the AC ripple and gives you a moving average.
The "abs(A)+abs(B)+abs(C)" * 0.333 gives the average of the three rectified phases.
The “*1000” is for the output of the current clamps (1 mV/A)
The “,50” describes the level of low pass filtering applied (50 Hz)
I hope this helps and thank you for taking the time to feedback on the error
Take care…….Steve
You are correct as this all comes down to the location of the brackets and mine are incorrect (thank you)
sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T) most certainly returns the collective RMS current of the 3 phases but the confusion arises with the multiplication by 1000.
Given the 3 phase flex probe and DC current clamps were originally used without the relevant custom probe settings, I have converted the values captured on channels A, B, C & D from voltage into current (probe output 1 mV/A)
Channel A, B, C & D are therefore multiplied by 1000 and converted to amps using the formulas A, B, C & D*1000
This is correct for each channel and should also be applied to the sum of the RMS values calculated in the above math channel.
As you have correctly pointed out, the location of my brackets (for calculating the RMS Current) results in only Channel C being multiplied by 1000 and not Channel A or B (highlighted in bold below)
“sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T)*(1000)”
The correct formula to multiply all phase values by 1000 is:
(sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T))*1000
Alternatively, sqrt(integral((A)^2)/T)*1000+sqrt(integral((B)^2)/T)*1000+sqrt(integral((C)^2)/T)*1000 can be used but the formula increases in size
I have added another math channel for discussion thanks to my colleague Jeff, this time looking at average motor current
- Av Motor Current
The "-" is to make it match the negative current draw of the battery (Channel D)
The "LowPass" smooths out the AC ripple and gives you a moving average.
The "abs(A)+abs(B)+abs(C)" * 0.333 gives the average of the three rectified phases.
The “*1000” is for the output of the current clamps (1 mV/A)
The “,50” describes the level of low pass filtering applied (50 Hz)
I hope this helps and thank you for taking the time to feedback on the error
Take care…….Steve