analogic pressure switch frequency

[padaddy]

I have a zanussi zwf 10020 fills but upon draining pump keeps running.

This machine uses athe elbi 7460 pressure switch, how many khz should I have output at full and empty?

Thanks

Paddy

[padaddy]

Re: analogic pressure switch frequency

I found out myself the sensors 0mm (empty) frequency is 44.75Hz I assumed it would be in the kHz range as in industrial equipment. Full frequency is 42Hz.

The designers factored in the slight vacuum created by the pump into their empty calculation. As the magnet in the pump gets weaker the vaccuum decreases and the computer assumes the machine is not empty. My pump works perfectly so I changed the tuned circuit in the pressure switch (transducer) to compensate.

[CJAPeterborough]

Re: analogic pressure switch frequency

congrats on an clever fix…how did you adjust the pressure switch and measure the frequency change?

[padaddy]

Re: analogic pressure switch frequency

The switch utilises a diaphragm pusching a ferrite into an air cored inductor. This forms part of a tuned circuit attached to a 12f629 pic which converts the signal into a remarkably linear output.

0mm of water is 44.75Hz – 300mm of water is 36.2Hz you can draw a straight line between the two to extrapolate the output graph. The machine expects a frequency lower than 0mm due to the slight vacuum created by the drain pump.

My initial thought was to take a couple of coils off the inductor to adjust it or stretch the internal spring but I thought I might get a pump at some stage and need to return the sensor to original. Instead I decided to replace the smt capacitor in the tuned circuit.

I don’t have an lc bridge so I estimated the required value by measuring the output with a 220p capacitor and a 10n capacitor. I estimated 760p which I didn’t have so I made by stringing 1n, 4.7n and 10n in series and the result was almost perfect. Washing machine now overfills slighty but works perfectly.

I measured the frequency with a multimeter, no need for an oscilloscope.

[boselecta]

well done for sorting that out.

Quite honestly this is beyond the technical abilities of 99.9{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} of domestic appliance engineers so the chances of getting a awnser to your initial question that would satisfy your technical knowledge on a component level are approximatly 0.001{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d}

[CJAPeterborough]

Re: analogic pressure switch frequency

I think most of us would fit a new Askoll pump for about a tenner.
You also have the possibility that the existing pump will drift further or fail completely of course……..

Fully applaud the elegant fix though!

[padaddy]

Re: analogic pressure switch frequency

While a pump may solve the issue in the short term the pump is not the problem, my pump still empties the washing machine quickly and I expect to get another few years out of it.

The root of the problem is that the programmers haven’t allowed enough tolerance in reading the pressure signal.

I found that a difference of just 0.2Hz which is equivalent to about 4mm of water in pressure terms was enough to tell the machine it was empty thats not enough margin.

[Martin]

boselecta wrote:Quite honestly this is beyond the technical abilities of 99.9{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} of domestic appliance engineers

You are so right however we in the trade have a more effective method of overcoming the problem, namely replacing the faulty pressure switch and clearing the sludge from the pressure chamber and hose system!

[padaddy]

Martin wrote:
we in the trade have a more effective method of overcoming the problem, namely replacing the faulty pressure switch and clearing the sludge from the pressure chamber and hose system!

and you’d have wasted your time there was zero sludge as it was used for about 2 weeks and the pressure switch output was *exactly* the correct frequency the previou owner had the engineer out who decided it needed a new controller

[Martin]

padaddy wrote:and the pressure switch output was *exactly* the correct frequency the previou owner had the engineer out who decided it needed a new controller

New controller? Engineer out? Could I please ask you to elaborate? 🙂

[padaddy]

I just changed the pump on another of these machines and the impeller was larger and a different shape to mine. Maybe askoll supplied a batch of pumps to zanussi with the wrong impeller?

Martin wrote:New controller? Engineer out? Could I please ask you to elaborate? 🙂

The machine was in a show house in one of Irelands many ghost estates so even though it was basically brand new it was out of warranty. The estates developer sold off the appliances to pay the bills and the new owner had problems from the get go. A repair man was sent by zanussi who said the pump was fine and that the machine needed a new pcb. I was given the machine for free as the pcb was too expensive.

[Martin]

padaddy wrote:A repair man was sent by zanussi who said the pump was fine and that the machine needed a new pcb.

Well I’m with the Zanussi guy on this, stick in a new PCB and, as they are not that costly, a new Pressure Switch as well.:D

Thanks for the up-date by the way.:tup:

[Jaunty]

Re: analogic pressure switch frequency

padaddy wrote:
….I don’t have an lc bridge so I estimated the required value by measuring the output with a 220p capacitor and a 10n capacitor. I estimated 760p which I didn’t have so I made by stringing 1n, 4.7n and 10n in series and the result was almost perfect. Washing machine now overfills slighty but works perfectly.

I measured the frequency with a multimeter, no need for an oscilloscope.

😕 😀 😕

I should have studied harder at science & engineering!

[Seamy]

Re: analogic pressure switch frequency

Did engineer hook up laptop to appliance to check output of analogic pressure switch? Normally it’s an update of the software that cures this issue, it can be seen in graph output when you run SideKick diagnostic programme on the appliance.

[Author]

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