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Please Help! I need some expert advice to specify a component

Discussion in 'General Electronics Discussion' started by Sean Coakley, Dec 18, 2014.

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  1. Sean Coakley

    Sean Coakley

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    Dec 18, 2014
    Hi all
    This is my very first time on here so a big hello to you all!

    Can you please help, I need to build and design a device that can monitor when an electric hydraulic ram is being forced against its will in a rest state. I am unsure if when the ram is forced whether it generates a resistance and if so is it possible to use this to trigger a relay or similar or if I need to be looking at something that will need to monitor the hydraulic side of things, I am an electrician by trade so please forgive my lack of knowledge in this field??

    Your help here would be gratefully received!

    Kind Regards Sean
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hi Sean and welcome. I don't know if your after a simple solution or if this will work. What about a simple micro switch which is triggered when the ram moves back beyond a certain distance. We call it a limit switch and if you could attach a plate of some kind to the ram you could put say a bolt through the plate, and have this activate the switch. Or something like that.
    Thanks
    Adam
     
    chopnhack likes this.
  3. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Welcome to Electronics Point, Sean! Can you provide a little more information about what kind of electric hydraulic ram you are using? These come in a huge variety of sizes and capabilities and configurations. And what do you mean "is being forced against its will in the rest state"? Last time I checked, hydraulic machinery does what you tell it to do, no will involved. What does "rest state" mean? Is the hydraulic ram connected to an actively powered load that can "push back" against the ram? Is the hydraulic ram being driven into a hard stop and you want to know when this occurs? Is the electric hydraulic pump an integral part of the hydraulic ram, which means you have no access to the hydraulic circuit? Do you have access to the internal hydraulic pressure applied to the ram piston? Is it a double-acting piston that allows the ram to be hydraulically driven in two directions (in and out)?

    The easiest way to detect a hard limit stop is to monitor the pressure driving the ram into the stop. When the pressure peaks and remains steady you can assume the ram has stopped. An adjustable pressure-sensing switch can perform this function.

    A more complicated way to sense a limit-stop condition is to mount a load-cell between the ram and whatever it pushes into. This is complicated because you will need to perform some mechanical design to attach the load-cell and use signal-conditioning circuitry to measure the load-cell output signal and determine when a specific load is reached or exceeded.

    As @Arouse1973 mentioned, a simple micro switch is the easiest, and by far the cheapest, way to detect a limit-stop condition. It will also require some mechanical design to place the limit switch properly. An over-running installation is generally required where a cam surface attached to the ram actuates the limit switch and then allows a certain amount of over-run while the switch remains actuated. This is preferable to placing a switch directly in the line of motion, where the switch can be crushed if the ram doesn't stop when the switch is actuated.
     
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  4. Sean Coakley

    Sean Coakley

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    Dec 18, 2014
    Hi Adam, Hi Hevans.
    Thanks for your feedback. What I'm trying to achieve is to be able to use, build, design a specific device for an automated gate system that is capable of monitoring when the hydraulic ram is being forced when closed and not in and open or close command. Ideally I hoped that this device could somehow be capable of monitoring this at the control panel end. Due to my lack of knowledge here I am unsure if this is even possible but hoped that perhaps something could be designed and built to acheive this function. For example do we know if the resistive readings coming back from the arm would change if force is being used against the ram and if so is their a device that can monitor this change and then operate a relay?

    Hevans your mention of being able to use a pre sure sense switch, do you think this would be easy enough to introduce onto the gate arm, again please forgive me I have no knowledge whatsoever here so I'm not even sure of the size etc of component you are speaking of.

    I am grateful for your help here so thank you once again!
    Sean
     
  5. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    So does the control panel already have a means of sensing the resistance? You say you have a resistance reading for the arm. If the ram is always pushing when the gate is closed and monitoring the control panel is monitoring the resistance then I assume pushing back on the ram will increase or decrease the reading on the control panel. Does it do this.
    Adam
     
  6. Sean Coakley

    Sean Coakley

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    0
    Dec 18, 2014
    Hi Adam
    The control panel does not already have the capability of being able to read a change in resistance. I am not even certain that the arm when forced will create a change in resistance I was assuming this and using it as an example and asking if you guys might know if it's possible. What I do know is that a faulty hydraulic arm can be diagnosed as being Electrically faulty if the resistance reading across the normally open and closed connections fall below 56/57 ohms. Usually a faulty arm would read 53 ohms or less.

    I am interested in Hevans idea of the pressure sensor switch and how that might be introduced?
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Ok just thought I would ask. Lets wait for Hop (hevans) and see what he can muster up.
    Adam
     
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