Testatika Small Machine Testbed 1 - April 20-21, 2005 - Testing front grids with most back grids

Warning: All test measurements were done incorrectly due to lack of experience using an oscilloscope with a floating voltage source (i.e. where neither electrode is grounded) - one electrode was always being grounded. As a result this information is useful for seeing how the device was constructed and the measurements are useful for historical reference only.

Three sets of tests are shown below for April 20-21:

Measuring voltage between front-center grid and back grids
Measuring voltage between front-center grid and front-side grid
Measuring voltage between front-side grid and back grids

For a clear picture of what grids are where, see the contruction page and look at the pictures up to April 18.

Note that for all tests there was also a 200mV AC signal from the household powerlines present. This affects what you see in the scope shots below. Note also that the disk was rotated at approximately 2400 RPM for all tests. This means that the disk was rotating at 40Hz and that the grids would see the wires at 800Hz (there are 20 wires).

1. Measuring voltage between front-center grid and back grids

Each cycle represents one wire pasing under the grids. This is clear since the cycles are arriving at around 800Hz (833.3Hz measured roughly in the picture).

A sample voltage for a cycle/wire is 132mV peak-to-peak as measured here.

This picture is a 'zoomed out' version of the above ones. Here you can see the reason for the larger cycles that the smaller 800Hz ones talked about above are riding on. It's the 60Hz household AC.

Note that the rotating disk is not perfect and so all 20 wires do not meet the grids on either side with equal spacing. This variation causes larger and smaller voltages and there is one wire that is especially different due to an error in construction. In this picture, the vertical cursors (lines) are positioned at two consecutive occurances of this. Notice that the measured frequency across these cursors is 40Hz (40.92Hz). This makes sense as 40Hz represents 20 wires or 1 complete rotation of the disk. You're seeing the same bad wire encounter the grids at both cursor locations.

2. Measuring voltage between front-center grid and front-side grid

The same as above, each cycle represents one wire passing the grids. The frequency measured roughly here is 833.3Hz.

The voltage of a typical wire passing the grids is 104mV.

3. Measuring voltage between front-side grid and back grids

The same as above, each cycle represents one wire passing the grids. The frequency measured roughly here is 833.3Hz.

The voltage of a typical wire passing the grids is 128mV.

Here I've 'zoomed out' again. This is the 60Hz household AC and how it's been affected by the small machine testbed. Notice that there is a cycle where you have a large voltage, then two smaller ones, then a large one, then two smaller ones, ... The frequency measured here for this repeating cycle is 20Hz (19.61Hz) and varies depending on the speed of the disk. I haven't figured out what it is caused by.