Elektor_Mag_-_January-February_2021

lektor January & February 2021 71

how the units are fixed in the case. Note the ready-made, standard

power supply that is used to power the Power Analyzer.

Figure 4c shows one of two extra brackets, which are added to prevent

the front panel from bending when test leads are plugged in or out. An

extra hole in the top and bottom cover must be drilled to attach the

brackets. I used a metal housing so the enclosure must be connected

to the mains Protective Earth, see Figure 4d.

Operation

After switching on, the measurement screen appears. It displays some

units and their values for the channel that is selected. At the top of the

screen you can select other channels (if available).

The screen can display a maximum of seven measurement values,

selected in the Configuration Screen.

Fast Fourier transforms are also calculated on the satellite boards. The
calculations are not invented by me but “borrowed” from [3]. Digital
filtering is based on chapter 16 of The Scientist and Engineer’s Guide
to Digital Signal Processing [4]. A Blackman-window is used and the
filter has 13 coefficients (M=12). The choice of the length of the filter is
a compromise between calculation time, memory needed and perfor-
mance (i.e. suppression of signals above 2.55 kHz and attenuation of
signals below 2.55 kHz).

Assembly
A front panel has been designed for a three channel version, which
can be ordered at Schaeffer’s. I used a metal case (order code 1510827
at Farnell, manufacturer Metcase, M5503110).

Figure  4 shows some detailed pictures of the hardware in this enclo-
sure, giving an impression of what the Power Meter can look like and

Figure 4a: The main board and display attached to the front panel.

Figure 4c: One of the extra support brackets between front panel and cover.

Figure 4b: One satellite board attached to the front. Note the extra isolation

(thick red tape) between the board and panel.

Figure 4d: PE-connection