The graphical results of plotting capacity vs. angle of vane enmeshment for a SLW variable capacitor with a nominal Cmax. of 520 pF.
[attachment=7679] [attachment=7680]
Remarks.
Graph 1 is a plot of angle of vane enmeshment vs. total effective capacity:
two curves: one without any series capacitor and one with a series capacitor of 150 pF.
Graph 2 is same, except that the vertical axis is the logarithm (base 10) of the total measured capacity.
There are 4 curves:
1: No series capacitor included;
2. Series capacitor = 470 pF;
3. Series capacitor = 270 pF;
4. Series capacitor = 150 pF;
At a first inspection, the curve on graph 1 with the 150 pF series capacitor looks like that that combination is what is required: a straight line (approx.), capacity vs. dial angle. But, of course, that is what we do not want, since in an L/C tuned cct. with a known and fixed value of inductance, f is proportional to 1/√C.
What is not obvious, however, is the nature of the relationship between vane enmeshment and the resultant capacity: the curve (no series capacitor) could be a variety of laws: all we can deduce is that that relationship is non-linear.
However, when we plot the log of the capacity against vane enmeshment angle (between 0° and 180°) - as per graph 2 - we can see that for dial readings from about 40° to 180° (no series capacitor), the curve is very nearly a straight line. Hence, the capacitor has a 'log-law' characteristic: this will correspond to a straight-line wavelength (SLW) variable capacitor.
The effect of introducing a series capacitor - and its effects on the law, as its value is changes - are very evident, as also is shown on graph 2.
Al.
[attachment=7679] [attachment=7680]
Remarks.
Graph 1 is a plot of angle of vane enmeshment vs. total effective capacity:
two curves: one without any series capacitor and one with a series capacitor of 150 pF.
Graph 2 is same, except that the vertical axis is the logarithm (base 10) of the total measured capacity.
There are 4 curves:
1: No series capacitor included;
2. Series capacitor = 470 pF;
3. Series capacitor = 270 pF;
4. Series capacitor = 150 pF;
At a first inspection, the curve on graph 1 with the 150 pF series capacitor looks like that that combination is what is required: a straight line (approx.), capacity vs. dial angle. But, of course, that is what we do not want, since in an L/C tuned cct. with a known and fixed value of inductance, f is proportional to 1/√C.
What is not obvious, however, is the nature of the relationship between vane enmeshment and the resultant capacity: the curve (no series capacitor) could be a variety of laws: all we can deduce is that that relationship is non-linear.
However, when we plot the log of the capacity against vane enmeshment angle (between 0° and 180°) - as per graph 2 - we can see that for dial readings from about 40° to 180° (no series capacitor), the curve is very nearly a straight line. Hence, the capacitor has a 'log-law' characteristic: this will correspond to a straight-line wavelength (SLW) variable capacitor.
The effect of introducing a series capacitor - and its effects on the law, as its value is changes - are very evident, as also is shown on graph 2.
Al.
