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Proximity Switches for a Bin Level Switch

11/26/2011 9:27 PM

I am working on an ice machine that has a magnetic reed contact for an ice level indicator.

The voltage or current is probably small - TTL or CMOS logic.

We have experienced two ice level indicator failures, and the magnetic reed contact comes as an assembly which is a little bit expensive.

Is there a two-wire proximity switch that will sense ice when ice contacts the indicator face?

Would this be a suitable application for a two-wire prox'?

It has to be a two-wire switch because that is what the old was. I do not want to have to get power off of the PC board or any of that engineering.

I can make a bracket to hold a typical prox', but I am uncertain about a 2-wire prox's ability to switch

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#1

Re: Proximity Switches for a Bin Level Switche

11/26/2011 11:13 PM

Maybe something in a bindicator? Not an endorsement. Not even sure this is a good idea.

Bindicator Product Selection chart

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#2

Re: Proximity Switches for a Bin Level Switche

11/26/2011 11:31 PM

How about a light sender/receiver/reflector?

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#3

Re: Proximity Switches for a Bin Level Switch

11/27/2011 11:18 PM

I recommend the Roto-Bindicator model. These are the most adaptive for changing material conditions. When the ice reaches the level indicator it will prevent the sensor from spinning and trip a contact.

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#4

Re: Proximity Switches for a Bin Level Switch

11/27/2011 11:21 PM

The magnet is on a float right? Can the assembly be disassembled?

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#8
In reply to #4

Re: Proximity Switches for a Bin Level Switch

11/28/2011 8:53 AM

No, I wish it we possible. The magnetic reed switch is molded into a plastic assembly. It looks to me like an good idea that isn't so good, if you know what I mean.

I should add that this ice machine is one step up from a consumer product - it is a ice machine in small to moderately sized restaurant. As ice machines go, ice machines are a major investment for a restaruant, and repairs to ice machines often a major expense.

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#5

Re: Proximity Switches for a Bin Level Switch

11/28/2011 1:02 AM

What is the make & model of this ice machine? I have worked on a couple and am interested.

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#9
In reply to #5

Re: Proximity Switches for a Bin Level Switch

11/28/2011 8:55 AM

This is a Hoshizaki KM-320MAH

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#17
In reply to #9

Re: Proximity Switches for a Bin Level Switch

11/29/2011 5:40 PM

My experience on Hoshi is that the float assembly is worn enough that the float is not coming up all the way and/or the float is too far from the prox. Even though Hosi parts are expensive, it will take a lot of messing around to re-engineer it. -- JHF

P.S. Make sure the float is not in the housing upside down. I've seen this more than once! Also, it is not a bin level switch, but a water level switch that controls the ice making cycle

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#6

Re: Proximity Switches for a Bin Level Switch

11/28/2011 3:26 AM

You didn't tell us "how" it failed.

Did you REALLY check this point out? It must be done as the failure may have little or nothing to do with being a reed switch (unöess of course the glass was broken!!)

Is the reed switch sometimes (accidently) placed in the path of the magnet for example? Probably due to tolerances in manufacture!

Photos?

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#7

Re: Proximity Switches for a Bin Level Switch

11/28/2011 8:17 AM

If you plan to continue to use the magnetic reed switch - before you replace it check the old one for resistance on the reed. If you find 5 - 20 ohms in the closed position you may be switching current and pocked the contacts. You can do this in static with small magnet. Going to a Mercury reed should solve that issue.

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#10
In reply to #7

Re: Proximity Switches for a Bin Level Switch

11/28/2011 9:00 AM

After a failure when you take the magnetic reed switch assembly off the machine, shake it up, maybe accidently drop it, it starts working.

When it works, it works good!

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#11
In reply to #10

Re: Proximity Switches for a Bin Level Switch

11/28/2011 9:19 AM

Sounds to me like very substandard quality reed switches......change the supplier.

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#12
In reply to #10

Re: Proximity Switches for a Bin Level Switch

11/28/2011 9:51 AM

Been there done that. Contacts on the reed switch are welded closed until you use "percussive diagnostics". Common cause is a capacitor in the noise filter at the input of the digital circuit. The cap discharges through the reed contacts and sooner or later makes them stick. Check the application notes for reed relay or switch manufactures and they should have tips to prevent this.

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#13
In reply to #10

Re: Proximity Switches for a Bin Level Switch

11/28/2011 9:53 AM

If you can shake it and it works - that could be a mis-oriented mercury switch. e.g. the switch could be upside down in the vertical position. Secondly, if not the mercury type and you are switching current then the reeds could be welded. Then broken loose from the shock of dropping if. The supplier should be able to tell you the reed type. Since they are a molded part You would need to specify to the supplier the type you want. Looks like design change time for the supplier e.g. an arc from voltage that is too high for the reed, if the reed is operating a inductance e.g. motor. etc.

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#14

Re: Proximity Switches for a Bin Level Switch

11/28/2011 10:33 AM

Magnetic reed switches are supposedly glass encapsulated to protect their tiny and fragile contacts. This glass encapsulation protect the contacts from wet or damp environment applications such as yours. The failures you are experiencing might be due to some physical or mechanical abuse that resulting to breakage of this glass encapsulation when the bin is accidentally subjected to unnecessary abuse? Preventing mechanical shocks such as dropping or banging the bins may solve your problem?

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#15

Re: Proximity Switches for a Bin Level Switch

11/29/2011 2:02 AM

A capacitive prox would work for ice and I'm pretty sure it could handle any current a reed switch could but I doubt the input circuit on the controller would be designed to supply the right power to a two wire prox. Check with the manufacturer.

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#16
In reply to #15

Re: Proximity Switches for a Bin Level Switch

11/29/2011 2:21 AM

Kind of what I am thinking to.

If it was switching a bunch of volts and some reasonably large current, OK.

But not TTL or CMOS voltage and currents (if that is what it is) - without a signal conditioner of some sort.

I tried measuring a voltage across the sensor terminals in both states. I am not sure what I saw, and I didn't at that moment want to mess around more. At any rate, it was not clear that way it was when I was trouble shooting a thermostat (27 Volts at almost an amp).

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