Elektor_Mag_-_January-February_2021

72 January & February 2021 http://www.elektormagazine.com

you go back to the Measurement Screen, the chosen formula with

the calculated value is displayed for all channels.

Back in the Configuration Screen you can also choose for Graphs->

Pressing this you can choose between Scope or FFT. Press Scope. This

brings you to select traces. Trace1 will always be displayed. A selected

trace will be high-lighted. All traces can be “connected” to a channel

and to V, I or P of that channel. The display will be “triggered” by a

positive zero crossing of Trace1. The display will give you an impres-

sion of the wave shape of the signals and their phase relation. Two

periods of the signal will be displayed. The amplitude of the signals

is always the same: voltage signals have the maximum amplitude. To

distinguish them from voltage signals, current signals are displayed

with a 80 % and power signals at 60 % amplitude. See for example

the waveforms of a transformer which goes in saturation in Figure  6.

The scope display doesn’t show absolute values, it’s just an indication

of shape and phase relation.

Back in the Graphic Screen, press FFT. This shows the FFT compo-

nents of a selected signal. On top of the screen you can select the

channel, LINear or LOGarithmic display and either V or I. The largest

harmonic (usually but not necessarily the first harmonic) is displayed

at 100 % or 0 dB. The horizontal scale gives the number of the harmon-

ics, not its frequency.

When entering the Logging feature, you must first select the time

period that you want to apply. Possible values are between 0.25 h

and 128 h in steps of a factor of 2. Next step is to select how many

traces you want to log (maximum three). Each trace can be linked

to a channel and from that channel you can choose either V, I or P.

Pressing Continue immediately starts the logging. An alphanumeric

screen will be shown, where you can watch the average, maximum

and minimum value and the elapsed time. You can also go to the

graphical screen. At the top of the screen you can select another

trace, if it is switched on. Pressing Return brings you back in the

main screen, the collected data are lost.

You can select Crest factor (V-CF or I-CF) in the configuration screen.

It simply divides the highest peak value (positive or negative) by the

RMS-value of the signal. Remember that the bandwidth of the measur-

ing amplifiers is 2.5 kHz, so this function is not suitable for audio. Only

until, say 250 Hz depending on your taste.

First go to the Main Menu (top right of the screen). Choose Configuration
and then the Configuration Screen appears with 16 values to choose
from. The selected values to be displayed are highlighted.

Some of these values will go without saying, but some need explana-
tion. Vdis and Idis (distortion) are calculated using:

Vdi s=

Vn^2

n= 2

40

∑

V 1

where VN stands for the amplitude of harmonic N of the signal.
Re-P means real power, P-VA means Vrms x Irms, Im-P means imagi-
nary power, and PF means power factor, i.e. Re-P / P-VA.
If you choose Eff-> you enter the Efficiency Screen. Here you can
choose the formula which describes the power relation that you are
investigating and then you go back to the Configuration Screen. If

BUILDING THE TRANSFORMER

Transformer TR1 is home made. Here is the recipe.

Ingredients (mentioned at the bottom of the parts list): two

core halves, two clips, one coil former, all for EF20, wire with

900 V isolation and diameter of max 1.3 mm.

> Take the coil former and cut off pins 2, 3, 4, 7, 8 and 9.

> With the wire make 9 turns between pin 1 and 10. You shall

exactly fill one layer.

> Repeat to make 9 turns between pins 5 and 6. Again you

shall exactly fill one layer.

> Put in the core halves and put on the clips. There is no air

gap.

> If everything went well, you will have a transformer with an

equal primary and secondary inductance of about 125 μH.

Capacitance between primary and secondary will be in the

range of 30 pF.

HOW TO CONNECT

There is a difference between connecting test leads for

measuring the power consumption of a load or measuring the

power supplied by a source, as can be seen in Figure 5. With

the indicated methods the voltage drop of the connection leads

and the current measurement section is eliminated. The voltage

difference between the I connections and the V- connection

must remain below 0.5 V. Otherwise the protection circuit is

triggered, and the power supply has to be cycled. Power AI Vnal yzer Power AI Vnal yzer

Load Load

• 
  
  
  
  • – + – + – +
  
  
  
  

Source Source

Measuring power consumed by a load Measuring power, supplied by a source

Figure 5. Connecting the test leads