Most of the inexpensive temperature controllers which use thermocouples as the input source report temperature in whole degrees and accept Sv inputs in whole degrees. Fuji, CAL, Love, and others can accept & display temperatures at 0.1 degree resolution. The inexpensive temperature controllers which can accept an RTD input can display in 0.1 degree resolution. To the best of my knowledge, the inexpensive temperature controllers DO NOT round off their displays, i.e. if you set Sv to be 226, a true Pv of 226.1 would display as 226 and a true Pv of 226.9 would also display as 226 when using thermocouples.Bushrod wrote:Fig 3 shows brew water at 235 for a group temp at 190. Figs 4 and 5 show Svs of 225 and 226. Why are these different for essentially the same group temp? . . . I'm getting some REALLY nice tasting shots.
The Silvia I have is modified such that I can read boiler water temperature and Figure 3 shows the relationship between my measured boiler water temperature and grouphead temperature at two slightly different Sv's (225, 226 F). Pv, which is the typical controller display, was sensed by an Omega washer-style thermocouple. The Sv of 225 produced an AVERAGE boiler water temperature of 233.6 and an AVERAGE grouphead temperature of 190.2. The Sv of 226 produced a boiler water temperature average of 235.4 and a grouphead temperature average of 191.9.
I did not bother to check the accuracy of these thermocouples because I was looking for a specific combination which would produce the Thermofilter logged shots shown. It is relatively easy (on the machine side of things) to get excellent temperature stability and more importantly, repeatibility, when the machine has fully stabilized. Conversely, the difficulty arises when you are pulling random shots and doing a little steaming between some or all of the shots. The fact that you are "getting some REALLY nice tasting shots" is what counts.
I would be interested in running some Thermofilter tests on your machine and you could publish the results. Give me a call at 301-587-5033 if you are so inclined.
edit - 08/22/07 - I now see where your confusion could come from and it is fault of my labeling. The shots were more of an afterthought because the purpose of the post was to show the effects of PID'ing. Why the grouphead temp was lower with a higher Sv is not known. In hindsight, I should have just pulled a shot after the three hours at Sv = 225 and again with Sv = 226.