Automatic cell frequency tracking.

Introduction.

As we have previously discussed the capacitance of a given water fuel cell is not constant because of gassing, consumption of the water in the cell and other factors. If that water capacitor is a part of a tuned circuit it is essential that the exciter follow these frequency excursions automatically. One means of doing this is by using a Phase Locked Loop (PLL) in the same way that Meyer did in patent WO 92/07861.

The 4046 PPL

Although it is not stated in the patent, I think the PLL he used was a CD4046 or equivalent, so I thought it might be of interest to have a closer look at this particular PLL integrated circuit.  I will attempt to make it as simple as possible for non - electronic types.  

A phase locked loop contains three sub circuits, a phase comparator, an integrator and a voltage controlled oscillator.

On the left is a  phase comparator, which feeds into the integrator and the output of the integrator feeds into the voltage controlled oscillator. The purpose of the circuit is to make the output frequency track the input frequency. If you want to know exactly how it works, you can download the data sheet from the internet.

The phase locked loop in WO 92/07861

Fig 1 in the patent follows ....

The point to remember is that the Water capacitor (resonant cavity) is going to change in value due to gassing and water consumption and this will cause the resonant frequency of the tank circuit to also change. The purpose of the phase locked loop is to adjust the frequency of the driving signal onto the new cell resonant frequency. Now if we look at the diagram for the adjustable Freq, Gen .....

 .....  We can see there is no electronic means to vary the frequency and the frequency can only be adjusted manually !. The other point to note that if there was a specific water resonance frequency why did he go to the trouble of introducing manually switched frequency dividers ?.

There is feedback to the Gated Pulse Frequency Generator but this only adjusts the duty cycle of the signal sent to the cell and not the frequency.

The two relevant extracts from the patent are ....

"The invention also includes a means for sensing the occurrence of a resonant condition in the water capacitor/resonant cavity, which when a ferromagnetic or electromagnetic core is used, may be a pickup coil on the transformer core. The sensing means is interconnected to a scanning circuit and a phase lock loop circuit, whereby the pulsing frequency to the primary coil of the transformer is maintained at a sensed frequency corresponding to a resonant condition in the water capacitor."

"In the invention, the water capacitor is subjected to a duty pulse which builds up in the resonant changing choke coil and then collapses. This occurrence permits a unipolar pulse to be applied to the fuel cell capacitor. When a resonant condition of the circuit is locked-in by the circuit, amp leakage is held to a minimum as the voltage which creates the dielectric field tends to infinity. Thus, when high voltage is detected upon resonance, the phase lock loop circuit that controls the cell driver circuit maintains the resonance at the detected (or sensed) frequency."

To complete this part of the story output G above feeds into a standard inverting switching circuit to drive the tank circuit.