Now we will make some current measurements with the Dewesoft X software and a measurement device.
We will measure the current which is consumed by a classic 40W light bulb and 11W energy saving light bulb. For this measurement, we will use two approaches, the first will be the direct voltage measurement on a shunt resistor and the other will be a measurement with current clamps.
Before the measurement we must do some calculations that will help us to choose the SIRIUS amplifier and range of the amplifier and current clamps. If we turn on both light bulbs the declared power will be 51W and the RMS value of the grid voltage is 230V, so let's take those numbers into our calculations.
After the rough calculations, we get the results that our RMS value of the current is approximately 0.22A. We know that the max value of the sine wave signal is √2 times RMS, but since the energy saving light bulb doesn't use the current in sine waveform we should have some reserve in our measurement ranges due to the higher crest factor of the energy saving bulb. This means that we will choose the 10A range on the current clamps and use the MSI SHUNT 5A adapter. The shunt resistance is 0.01Ω which means 1A current will cause 10mV drop on shunt. This information is needed when we are setting the measurement channel on which we measure a voltage drop on the shunt. Since Dewesoft MSI adapters are already equipped with this information, the software is able to configure the setup in the correct way. This is one thing less for taking care of when we are using Dewesoft MSI adapters.
Now we can start with our measurement. We will use two different SIRIUS amplifiers, LV and ACC. Let's see how the connection for our measurement looks like. Current clamps are directly connected to the ACC module and the MSI SHUNT 5A adapter is connected directly to the LV module like on the photo below.
As you can see in the photo we must split the wire for the shunt installation. This can be dangerous because of the grid voltage and we should be careful when doing this at home. Now let's see how the configuration of channel 1 with the shunt is done. First we rename the channel to Shunt current so we will later know the output of which sensor's output we are looking at when the measurement is in progress. Physical quantity should be set to Current and Unit is set to Amperes(A) by default. Once these settings are done we should "calibrate" our sensor. We will choose calibration by two points in this case because we already know that 1V equals 10A. We just simply type this two values in the prepared place. If we set all the parameters correctly and the classic light bulb is turned on, we can already see the sine form of our current in Scope mode on the left bottom side of the setup window.
For channel 8, where we have connected the Current clamps, the settings will be a little different because we are using HV module for this measurement. Since the current clamps are set on 10A range they provide 1mv/1mA on the output (scaling factor is 1). That means we can't get more than 10V on output and range of our amplifier should be set to 50V to achieve greater resolution of the measurement. We should also set the Physical quantity to "Current" and measured unit to Amperes.
In the next snapshot, you can see the combined waveform of the energy saving bulb and the light bulb. The waveform changed mostly due to the non-sine waveform and the high crest factor of the energy saving light bulb.
Now when we switch to Measure mode, we can see the phase shift of the current clamps compared to the shunt resistor. At first sight, there is no big phase shift(around 10°) on the picture below, but with applications like the power measurement phase shift is very important for correct results. The phase shift is around 10° in the picture below, and can influence the measurement results for detailed power analysis significant (especially reactive and apparent power). The phase-shift of this current can be compensated using the sensor editor.
Calculate the AC RMS value
To see the RMS value of the current signal, add a Basic statistic math function.
Select the input channel (current signal) and the RMS as the output channel. We can display one value per measurement or we can display new values for each defined block of data.
Another option is also to display the RMS value of the signal directly in the recorder. Select the RMS as the Display type (in the left corner of the screen).