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Thread: Digital pressurestat

  1. #1
    Senior Member Jackster's Avatar
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    Digital pressurestat

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    I have a hx machine and it has a mater pressurestat.
    The deadband on the pressurestat is 0.5 bar. So setting it to turn the element on at 1.0, has it turning off at 1.5 bar.

    This seems like its too big a variance.
    What are others variance or deadband like?

    Anyway, pid unless linked to pressure is a overkill, so thinking i could digitise the pressurestat for less than the price of a siria. Gaining a ssr, and tunable deadband and adjustable top and bottom switching from a pressure sensor, not temperature.

    So, this guy Julian Edgar is awesome, does electronics, car tuning and a amazing array of stuff and is cool enough to write it all down. Its a ezine called autospeed.
    Anyway, he talks about a voltage switch in one article here:
    AutoSpeed - Digital programmable voltage switch
    The boards are now $5 on ebay...

    The way i see it, if i add a power supply, and a 30psi sensor, and a ssd relay.
    I will have digitised the pressurestat with no moving parts and easy adjustability.

    Just quietly, duplicating the system but using a 150psi sensor in the brew curcuit, would eliminate the opv in vibe pump machines.

  2. #2
    Senior Member Jackster's Avatar
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    The deadband on this board is 0.2v, i think if using a 30psi sensor this would equate to a minimum of 0.1bar (1.2psi) deadband. I think this would be too small, but as you can adjust the deadband larger, its no problem. Even if you wanted that fine a control, you would have a ssr in there, so that would be doable.

    I welcome any input, as im not a guru at electro-mechanics, or coffee either...
    Cheers

  3. #3
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    Sounds like an interesting mod...
    I am not sure how you want to eliminate the OPV though with only a pressure sensor.

  4. #4
    Mal Dimal's Avatar
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    It all sounds good in theory Jackster but just a decent pressure tx-ducer on its own will set you back ~$100 or more. You then have to condition the output to ensure it interfaces properly with the device you linked to, or something similar. Most of these tx-ducers use common process control output ranges such as 4-20mA, 0-10V-, etc. Would make more sense to use an Arduino or Raspberry Pi and experiment with that. Would probably be fun...

    And as "degaulle" mentions, you need a lot more than this to manage pump pressure or simulate an OPV...

    Mal.

  5. #5
    Senior Member Jackster's Avatar
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    Thanks guys,
    There is stainless 3wire 5v 1/8 npt 30psi pressure tx for $17
    With a combi 12/2a + 5v/2a hard drive power supply for $7. 12v for the board and 5v for the sensor.
    $5 for the board....

    The board accepts any voltage input from 0-60v as a switch voltage.

    The ebay newer version also includes a timer. So could use it as a shot timer (need to change the timer to use 1/10th sec rather than minutes..somehow)
    Or a digital grinder timer.

    Would love to know more about arduino, but my eyes glaze over whenever i try to understand the programming. The hardware stuff im fine with, software is grrr.

    I remember typing stuff into a vic20 for a day, just to make a pixel bounce about the screen. 1 mistake and aaarghhh, why wont this work....guess its a hangover from that

  6. #6
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    Why focus on pressure ?
    What you are ultimately trying to control is temperature, so why not just use a digital thermostat.
    They are similar to a PID without the sophisticated control programs, but able to control the boiler temp within 1deg.
    Generally they are used with an SSD but some are available with 10, 20 , or more amp relays built in.
    priced at about $20-$30 (Ebay ?) complete with temp sensors
    Typical example..eBay link removed as per Site Posting Policy
    I converted several machines using these and posted threads on here a few years ago giving the details
    Here was a thread with some of those details
    http://coffeesnobs.com.au/brewing-eq...tml#post562446
    Last edited by Javaphile; 19th February 2018 at 11:27 AM. Reason: eBay link(s) removed
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  7. #7
    Senior Member Jackster's Avatar
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    I think the pressure and temperature are closely linked, but plenty of writing here says that temp sensors are not that good on a hx boiler. Too big a delay or lag?

    A ssr just saves the switching contacts on a relay. I can see the benefit of these even coupled to a standard pressurestat.

    The board i linked would just as easily run a temperature input.
    I looked at your link, my board is very similar. Just more adjustable, but would need to convert the voltage to a temp or pressure.

  8. #8
    Senior Member Jackster's Avatar
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    Paste this number into ebay.
    172991256098

    I looked at yours blend52. And got a similar one. I have another little job ventilating a roof space. It will be perfect.
    Last edited by Jackster; 18th February 2018 at 11:31 PM.

  9. #9
    Mal Dimal's Avatar
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    $17.00 for a pressure tx-ducer...

    Must be a good'n.

    Mal.

  10. #10
    Senior Member Jackster's Avatar
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    Found your old post mal.
    My pressurestat def doesnt have a deadband of 0.05 bar.
    Thought it was wrong.
    Im not looking at a pid, but i either need a new pressurestat or some tighter control of boiler pressure. 0.5 bar variation is a bit much.


    Quote Originally Posted by Dimal View Post
    Great post Attilio..... [smiley=tekst-toppie.gif]

    To back up what Attilio has said, in an HX espresso machine it is almost bordering on ludicrous to suggest that boiler temperature should be controlled by a PID Controller. It just makes absolutely no sense at all.

    The Primary purpose of the Boiler in a HX machine is to supply good quality Steam at preferred volumes and rate of delivery. The Brew Water Temperature is controlled, not by the temperature of the water in the Boiler so much but by the design of the Heat Exchanger system, the Group and how the water is delivered from the Boiler to the Group.

    A standard Pressurestat in a so-called Prosumer machine, will maintain Boiler Pressure at +/- 0.05Bar. This equates to a Temperature range from nominal of +/- 0.8C or expressed in another way, a peak temperature of 1.6C above the nominal setting. This is NOT the range of temperature variation reflected in the Brew Water as this is totally dependent on the HX system design as a whole. If you were to substitute the Pressurestat for a PID Controller, sure, you would be able to control the Boiler Water Temperature to a much tighter band but the only place youre going to see this (if it is at all possible) is in the Temperature of the Steam being delivered, not the Brew Water.

    If you want to attain the sense of having absolute control over the Brew Water Temperature, then you need to to start thinking decent quality Dual Boiler machines with one of the Boilers dedicated to the Brew Water. Alternatively, buy a Silvia, Quaha/Imat/Nemox/Lelit style of machine and dedicate this to pulling espresso only.

    HX espresso machines with PID Boiler Control is an absolute furphy but, if you like looking at bright LEDs and pushing buttons, then go for it..... :

    Mal.

  11. #11
    Mal Dimal's Avatar
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    I'd suggest getting in contact with one or more of the Site Sponsors closest to you, and see what they can recommend for you.
    There are several P/stats around that can operate within a hysteresis of 0.2 Bar or less, which is plenty good enough.

    Mal.
    P.S.
    0.1 Bar should have been 0.2 Bar.
    Last edited by Dimal; 20th February 2018 at 04:48 PM.

  12. #12
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    Just to add to this a little , and trying to be practical.
    I have had several "prosumer" hx machines with various pressure stats (Jager, CEME, MATER, ) and none of them have ever indicated a deadband of less than 0.2- 0.5 bar. Few of them have lasted more than 3-4 years before failing one way or other. ( stuck ON usually !)
    They are also not cheap at $40 - $60 each with out installation and set up costs if you dont do it youself.
    However, as mentioned above, on a decent hx machine (E61 or similar) the boiler temp is not critical to the brew temp, so its not worth a PID...or in my opinion an expensive, unreliable, Pressurestat....when a cheap digital thermostatic control will perform just as well if not better. Modern thermocouple sensors are much faster response and smaller deadband (0.1 deg) than the old bimetalic thermostats used in basic machines like the Silvia etc.
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  13. #13
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    Jackster have you recorded both your Temp and Pressure (as delivered at espresso flow rates ) at
    the grouphead?
    The input given previously is accurate. That being that the swing in pressure as shown by your boiler press gauge
    has little effect at the g/h at that point of time.
    Further reference for you, look up The Coffee Machinist, Melb.And read his threads on his site and here.
    GL
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  14. #14
    Senior Member Jackster's Avatar
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    Behmor Brazen - $249 - Free Freight
    Im still in process of fixing this machine (musica) and waiting for parts to arrive.
    Just the 0.5 bar variation seemed too much.
    I have a digital thermostat coming, so either way will sort something out.
    I citric acided the ma-ter last night and its improved a little...

    I still have some other issues to attend to with this machine, so will track temp after i fix its leaks.
    Also a pressure gauge is intended.

    Coffeemachinist is a pretty cool site! Lots of things going on there.
    Thanks guys. I have a few things to consider.



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