DC input RMS value calculation in drift window of 500ms

Thread Starter

Avinash B P

Joined Mar 2, 2022
10
I want your support for finding any IC solution for monitoring the DC voltage in the time window of 500ms and generate the output voltage proportional to the value average value in the 500ms window.

Is integrator can be used?
What are all the parameters needs to be considered.



Regards

Avinash B P
 

crutschow

Joined Mar 14, 2008
29,799
The easiest and most accurate would be use a microprocess to take 5-10k A/D samples in that 500ms window, average the samples, and then generate the analog output with a D/A converter.

If you want to do it with analog circuitry, you could connect the voltage to a 1s time-constant integrator for 500ms.
The output voltage will then be 1/2 the (negative) average of the input.
You then need to reset the integrator to zero volts for the next integration.

Below is the LTspice 1s time-constant integrator simulation for a +15Vdc input voltage with a superimposed10Vpp, 1kHz ripple.

1647877567410.png
 

Thread Starter

Avinash B P

Joined Mar 2, 2022
10
Hello Crutschow,

Thank you for your suggestion. I am using the same circuit. With 1 gain. I am thinking of how to reset the integrator. Could you please suggest some ideas.

Regards
Avinash B P
 

crutschow

Joined Mar 14, 2008
29,799
Below is a simulation using a small N-MOSTET with a PNP level shifter to reset the integrator (shown with a 0.5ms reset pulse).

1647881677003.png
 
Last edited:

Ian0

Joined Aug 7, 2020
5,147
Folks, don't forget that he said RMS.
So you have to square the sample values, then average them, then take the square root.
There are RMS-to-DC ICs such as THAT2252 but the application circuit is for AC input, so it would have to be DC coupled.
 

crutschow

Joined Mar 14, 2008
29,799
Unless the ripple voltage is a high percentage of the DC voltage, it should have only a small effect on the measured average voltage value versus the true RMS value.
For example in my simulation for a 15Vdc level with a 4Vpp sinewave ripple, the Vrms value was 15.062V, just 0.4% above the average voltage.
 
Last edited:

Ian0

Joined Aug 7, 2020
5,147
He might be measuring the current between a rectifier and a smoothing capacitor, or a battery charger. The application wasn’t specified.
 

Ian0

Joined Aug 7, 2020
5,147
Ok, so you don’t need RMS, average voltage will do.
if you need a value for the ripple, then there is a neat way of doing it using the maths that calculates standard deviation.
 

Thread Starter

Avinash B P

Joined Mar 2, 2022
10
I am measuring the HT line of 0-1500V Using DVL1000. The proportional output of DVL is current 75mA for 1500V. My proper voltage window 450V to 930V will considered as voltage is in the window and anything below 450 and Above 1050V considered as out of window. for this i am monitoring the DC voltage having ripples in 500ms time.
 
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