Table of Contents. Electrical Technology 2 3 minutes read. Show More. Related Articles. Electric Bill Calculator with Examples. F Improvement. Your explanation is very helpful for electrical people. Leave a Reply Cancel reply Your email address will not be published. Check Also. Close Search for. Adblock Detected Our website is made possible by displaying online advertisements to our visitors. Please consider supporting us by disabling your ad blocker. We depends on ad revenue to keep creating quality content for you to learn and enjoy for free.
The datasheet of the AD tells about the two most important factors that should be taken into account to calculate the percentage of error that this IC will produce while measuring RMS value, they are. By observing the curves on the graph, we can observe that the frequency response is not constant with amplitude but the lower the amplitude you measure in the input of your converter IC, the frequency response drops, and in the lower measurement ranges at around 1mv, it suddenly drops a few kHz.
I assume now you can understand the rest values. NOTE: The frequency response curve and the table are taken from the datasheet. In simple terms, the crest factor is the ratio of the Peak value divided by the RMS value.
For example, if we consider a pure sine wave with an amplitude of. You can clearly see that from the below image taken from wikipedia. The table below from the datasheet tells us that if the calculated crest factor is between 1 to 3, we can expect an additional error of 0.
The below schematic for the RMS converter is taken from the datasheet and modified according to our needs. As shown in the schematic, an input attenuator is used which is basically a voltage divider circuit to attenuate the input signal of the AD IC that is because the full-scale input voltage of this IC is mV MAX.
Now that we have clear some basic facts about the circuit let us begin the calculations for the practical circuit. Now if we put these values in an online voltage divider calculator and calculate, we will get the output voltage of 0. That is the output of the voltage divider circuit. That is the output voltage from the AD IC. Now you can see that the above theoretical calculation and both the multimeter results are close, so for a pure sine wave, it confirms the theory.
The measurement error in both the multimeter results is due to their tolerance and for demonstration, I am using the mains V AC input, which changes very rapidly with time. At this point, I did not bother to use my hantek BL oscilloscope because the oscilloscope is pretty much useless and only shows noise at these low voltage levels. For demonstration, a PWM signal is generated with the help of an Arduino.
The voltage of the Arduino board is 4. Now put these values in an online voltage divider calculator and calculate, we will get the output voltage of 0. In theory, a True-RMS multimeter will easily be able to calculate this theoretically calculated value right? The transformer in the image is sitting there and doing nothing. With that, you can see I am a very lazy person. Before anybody jumps and says we have done the calculations wrong, let me tell you we have done the calculations right, and the problem is in the multimeters.
In DC mode the multimeter is simply taking the average of the input signal which we can calculate. So, the input voltage is 0. In AC mode, the input capacitor of the multimeter is blocking the DC components of the input signal, so the calculation becomes pretty much the same. Now as you can clearly see that, in this situation both the readings are absolutely wrong. So, you cannot trust the multimeter display. The AD is a kind of IC that is used to measure these types of input signals accurately.
The below image is proof of the theory. Now we have calculated the RMS voltage to be
0コメント