Post By Lyrebird
"Thebat device" Grouphead thermometer
There's previously been some discussion about E61 grouphead thermometers but I haven't found specific mention of TheBat device version.
Nothing ground-breaking about the design, just a different take on mounting to the grouphead compared to "Eric's device" which uses a modified Swagelock compression fitting to seal against the thermometer probe. With his, the tip of the thermometer is directly exposed to water in the grouphead when it is flowing. The downside however is the aesthetics.
Thebat device uses a modified hex head cap screw, (similar to what you remove to install this one), which has been blind drilled for a tolerance fit of the thermometer probe. The last few mm have been turned down externally creating a thinner tip for quicker heat transfer. This modified screw "thermowell" has thermal paste applied internally before installing the thermometer probe to ensure the best possible heat transfer. In effect it's the same as Eric's device just with an additional thin layer of metal over the thermometer tip. Sensitivity would be near identical. The big benefit is that the overall installation is a lot neater and less obtrusive. It looks like the original screw-head with a short length of probe and smaller thermometer head on it.
(photo from web)
Just a mention regarding cost. Both Eric's device and Thebat device seem quite expensive for what they are. As they aren't mass produced, the price reflects the effort involved. There is a fair bit of manual labor involved in modifying the length of the thermometer probe and also the mounting components to suit. The thermometers in themselves aren't expensive its just the labor component that determines the price.
Anyway, first impressions are mixed. I always start machine warm-up by running water through the grouphead and then lowering the lever to the middle position (not fully lowered to drain). This leaves water rather than air gaps in the grouphead which I believe helps with quicker and more even heating. Its early days but I've come to the conclusion that temperature readings are only indicitive and not accurate when there is no water flowing in the grouphead. Part of the reason for this may be explained by the image below. What are referred to as "Infusion channels" in the image are shown to rise towards the "plug" (which is replaced by Thebat device mounting screw) and then fall towards the "Dispersion screw" (diffuser). I believe that when there is no water flow, the water drains out of the falling section of the "Infusion channels" leaving the tip of the thermometer or thermowell just short of the water in the rising section. There will still be radiated heat from the surrounding metal but you won't get a true water temperature at rest.
However, when the E61 grouphead has been given time to fully heat-up, the temperature displayed is closer to the brew-water temperature. You see much less variation between rest temp & when brew-water is flowing. It takes the initial couple of seconds of flowing water before actual water temp is displayed but you learn to allow for this. The closer to optimal grouphead temp, the less time it takes. On my machine (Vibiemme E61 Single Boiler), once past this, I have about 0.5 deg C variation over the 25-30 sec brew cycle. I still flush 3-5 secs before brewing depending on how close to the previous heating cycle it is. If insufficient (slightly) heat-up time has been allowed, the temperature will fall 2-4 deg C during brewing which isn't desirable. At the moment I'm experimenting with controlling temperature in the 2nd shot as I sometimes see a 2 deg c rise if brewed too soon after re-heating occurrs following the 1st shot.
I found Thebat device has given a better insight into the timing of grouphead heat-up and also timing requirements between shots. Originally I set the machine thermostat to 93 deg C using a multimeter and bead thermocouple as water exited the shower screen. Yet to compare the 2 readings but on the to do list.
Last edited by CafeLotta; 11th June 2018 at 02:31 PM.
Photo of Thebat device thermometer installed in Vibiemme E61 grouphead.
Following a PM from a CSer, a little additional information is added here. "The batdevice" is/was made by a coffee enthusiast from Denmark in a "cottage industry" style situation I gather. I'm not sure of the current status of further supply.
I haven't found these or similar devices sold by anyone directly who is located in Australia.
It appears he does them in batches and originally sold them via a Danish Coffee Forum - Sælges "Thebat Device" - Tag temperaturen på din E61 (you need to right click and select translate to English). They were also sold via Ebay.de.
I bought mine from Ebay.com.au. It was listed as the last one in that particular listing and as of today there is no re-listing. Price was around $130AUD landed here which is less than "Eric's device" from the US - https://www.chriscoffee.com/e61-digi...r-p/sss-04.htm.
A couple other variants I found in my travels are linked below but I know nothing more about them.
From Korea (Translation required) -
Mimesis is..... :: Vidastech - E61 Thermometer
ë””ìžì¸ì»¤í”¼ | DESIGNCOFFEE
From Romania -
PS - I have done a quick test comparing the Grouphead thermometer to a bead thermocouple and multimeter (as best as you can) under the shower screen with brew water running and found 1-2 deg C lower under the shower screen as you would expect. I seem to remember 2 deg mentioned elsewhere as the variation between the two.
Last edited by CafeLotta; 14th June 2018 at 12:44 PM.
Thanks for all the information. Do you plan to leave the bat device in permanently or just for testing?
Ps Any idea why you can't have English as a first language to produce these devices?
Yeah will be leaving it in permanently for now. Its interesting how addictive it is playing around with different forms of flushing to try to speed up the heating phase of my older VBM E61 single boiler. Turns out I was pretty close to the mark before installing the thermometer. On my machine, the standard 40 min heat-up came in a bit low on temp without flushing some hot water during this time.
Originally Posted by 338
The market probably isn't big enough here to produce these commercially and America has Eric's device. I think we're too accustomed to click and buy where there are no borders! Also the results from these thermometers aren't absolute and need a bit of interpreting I feel. You need a couple of seconds of running brew water before any useful reading appears. Probably not suitable for the majority of people who just switch on and wait 40 mins.
Originally Posted by 338
Last edited by CafeLotta; 14th June 2018 at 06:06 PM.
Found an image which shows more clearly how these type of thermometers mount and better explains my comment above.
Originally Posted by CafeLotta
Vidastech E61 Thermometer.jpg
I'm currently building a combined thermometer / pressure sensor that screws into the m6 thread on an E61 group to enable me to test something else I dreamt up. Mine interfaces with an industrial PLC (because the thing I dreamt up is PLC controlled anyway) but it would be simple enough to give it a dedicated readout.
I'll post some info when it's built and tested.
Spotted this Isomac Dual Boiler that comes standard (?) with a pressure gauge mounted in this location. I was always under the impression that a pressure gauge measuring liquid should be mounted in a location where air can't enter the gauge (low point). Air compresses, water not really. Maybe the relatively low pressure and minimal air pocket don't really affect the pressure reading to any large degree. This location on the grouphead is at a high point in the brew water circuit and also appears to drain so I can't really see how an air pocket doesn't form at this high point. When brew water is flowing I'd imagine the majority of air is pushed through.
Originally Posted by Lyrebird
Isomac Pro Dual Boiler Gauge.jpg
Pressure is distributed force so it doesn't dissipate.
If you have a look at the pressure gauges on any standard machine you'll notice they have pigtails between them and the boiler(s). These serve to prevent water ingress into the Bourdon tube in the gauge by maintaining a column of air / steam as a buffer but allow the system pressure to be transmitted to the gauge. This slows down the response of the gauge but it will reach equilibrium eventually.
Since the pressure fluctuations I wish to measure are fairly slow I believe the same principle will apply when I mount the pressure sensor to the grouphead.
I'll soon find out if I'm wrong.
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