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"Thebat device" Grouphead thermometer

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  • #16
    Made an interesting discovery today when tinkering around with a different type of grouphead thermometer. I was under the impression that the ideal mounting of a thermometer was with the tip in line with the edge of the water gallery that goes downward toward the water diffuser and shower screen as per the image.

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    I discovered on my VBM that TheBat device has the sensor tip about 3mm past the bottom of this opening. May need to try an extra washer or 2 although it does seem to work ok as is.

    I made a simple gauge to measure the position of the opening as it heads downward. Did see this somewhere a while back. The gauge is a straightened paperclip with a tight fitting piece of insulation stripped off a wire. The hook end is carefully slid down the hole where the thermometer mounts, until the hook drops into the opening heading downward. Raise slightly until you locate the upper edge of the opening. Hold steady while you slide the insulation sleeve down the wire until it stops at the surface where the washer normally sits. This will give a dimension to be able to judge where the thermometer/thermowell tip sits.

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    On the Vibiemme, there is 10mm between where the washer sits and the top part of this opening/gallery heading down to the diffuser/shower screen. The gallery seems to be around 2mm or so to the bottom making 12mm overall. TheBat mounting screw ia 15mm from the washer contact surface to the tip.

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    • #17
      After using TheBat device for a few months, I finally got around to trying out "Eric's device" which is one of the more established grouphead thermometers available. There has been alot written on the "Home-barista" website about it and Eric has posted there also giving his insights into its use as well as development of his product -

      My interest was in how "Eric's device" compared to the less expensive "TheBat device" and the even more affordable "CoffeeSensor" grouphead thermometer.

      Eric's device is quite expensive here in Australia as it needs to be shipped from the USA. I've only ever seen one used unit up for sale and grabbed it for about half the new price.

      In use it is quickly apparent that Eric's device is much more sensitive than both "TheBat device" and the "CoffeeSensor" which have similar sensitivity.

      The VBM E61 grouphead design seems to differ externally to some others and Eric needed to modify his mounting fitting early in development for clearance on the VBM. I had issues installing the current CoffeeSensor on my VBM needing 5mm of washers just to clear the grouphead and another 4-5mm of washers to get the probe tip near the correct position. CoffeeSensor are aware of this issue with the VBM and will be modifying their mount to suit in an updated version. Even though it was leaking due to all the washers, it allowed me to do a quick comparison of TheBat group thermometer to the CoffeeSensor. In use, these 2 appear to behave in a very similar fashion with a slight lag in updating temp when compared to Eric's thermometer. I'm still trying to decide if this slight lag is actually a good thing as it knocks off the highs and lows of displayed temps to a point. This stops the temp display fluctuating so quickly and eliminates displaying momentary temp spikes. After a week or so I'm still getting used to how sensitive Eric's thermometer is and tend to get distracted by the rapidly fluctuating temp display. Whether this degree of sensitivity is actually needed when brewing compared to the slightly less sensitive "TheBat device" and CoffeeSensor, I'm still not sure. It is interesting seeing the momentary spikes in temp (especially high) but I'm still experimenting with whether these can be minimised. This is most evident flushing between shots and flushing trying to speed heat-up.

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      "TheBat device" on the left, "Eric's device" in the middle, "CoffeeSensor" on the right.

      Summary of pros and cons (in my opinion).

      TheBat device
      Pros: Easily installed, Compact design, least obtrusive, small Thermometer head, price, Thermometer removal leaving screw in place
      Cons: Availability(?), price, thermal paste inside thermometer mounting screw can dry out (easily replaced)

      Eric's device (early days of use)
      Pros: Sensitivity, easily adjustable insert length, Thermometer head quality, well developed design, back-up
      Cons: Price, obtrusive aesthetics, maybe too sensitive(?)

      Pros: Affordability, Back-up support, reasonably compact, easily installed
      Cons: Current design has issues mounting on VBM, buttons on Thermometer a bit more awkward to use, insert depth (too deep?)
      Last edited by CafeLotta; 10th November 2018, 11:13 AM. Reason: additions


      • #18
        Correct insert depth for Temp probe

        The attached PDF is the earlier version of the manual for Eric's grouphead thermometer. Determinig the correct insert depth for his thermometer is discussed on page 8 and is applicable to all grouphead thermometers I'd imagine. It's also what I used as a guideline when installing "TheBat device" and the "CoffeeSensor" and avoids creating an undue flow restriction in the Brew water path. This is especially relevant with the larger diameter probe/thermowell tips of TheBat and CoffeeSensor. Eric's thermometer is the only one of the three which has the actual thermometer tip exposed to brew water.

        This PDF will ask to be saved to your local drive. Couldn't work out how to attach it as a view and not download PDF.
        Attached Files
        Last edited by CafeLotta; 11th November 2018, 10:51 AM.


        • #19
          I've had Eric's grouphead thermometer installed permanently for about 3 months now and thought I'd post an update. As mentioned previously it is the most sensitive of the 3 grouphead thermometers I tried as well as the most expensive.

          With each of the thermometers there is a learning curve and switching from TheBat device to Eric's thermometer was almost like starting over again due to it's greater sensitivity. The readings spun through quicker and reached higher and lower readings as temp spikes were displayed. These spikes weren't displayed on TheBat device due to it's slightly lower sensitivity. This could be viewed as a good thing in a way as it lead to less confusion in interperating readings. I can only comment on my observations in regard to a single boiler E61 machine.

          Eric's device will remain permanently mounted on my machine as I like the solid and quality feel of the unit as well as the added sensitivity. If price isn't a big issue I'd give it a big thumbs up. If price is a consideration I found that both TheBat device and CoffeeSensor were on par in regard to sensitivity. I used TheBat device for a few months and found it invaluable. I really can't see how any non-PID E61 single boiler would manage tight temperature consistency without a grouphead thermometer to guide the brewing process. Might explain the demise of E61 Single Boilers. If Grouphead Thermometers were standard equipment on them it may have helped unlock their full potential. Even PID versions might benefit from monitoring actual E61 grouphead temperature between shots and initial heat-up. Alot has also been written in regard to the usefulness of grouphead thermometers on Hx (Heat Exchanger) machines.

          As mentioned in a different thread, I believe the original CoffeeSensor has been updated so that the mount now works with VBM Groupheads without using multiple washers. There is also a "Pro" version in the works that appears to have adjustability in a similar way to Eric's device -


          • #20
            Interesting review, thanks.

            FWIW what you are calling sensitivity appears to be response time, in metrology these are different things: sensitivity refers to the minimal difference in the measured quantity that will cause the instrument reading to change.


            • #21
              Sounds about right. Eric's thermometer has had the probe housing the sensor manufactured to a minimal wall thickness aiding heat transfer between the brew water and the sensor. The quick response time is very obvious when compared to the other 2 thermometers I tried. Not entirely necessary but can be of use if you so desire.

              This has been useful to me when I have played around with seeing how venting some steam through the steam wand between shots affects temp stability during the next shot. On my single boiler I can actually tighten the temp variation a little during the shot (to <1 deg C, at times 0.5 deg C). I've also thought I might play with opening the steam valve a little during a shot to play with pressue (profiling a bit like a paddle?) and see what it does to temp during the shot.


              • #22
                Originally posted by Lyrebird View Post
                I've just worked out a neat way of doing a grouphead thermometer for vastly less than the above devices. Andy if you are reading these threads, it could be a good addition to BeanBay

                Did you ever complete this design??? (Asking for a friend)