# Is the MeCoffee PID being used outside its range of operability (max 100°C)?



## phario (May 7, 2017)

A number of people have noted issues with unreliable temperature control in the MeCoffee PID, particularly as it concerns the steam operation.

From @davidk21770



davidk21770 said:


> My issues were with the claim to be able to control the brew pressure -- change the brew pressure/add an infusion delay using pressure as a function of time. Doesn't work at all. Never got any response to emails for help from MeCoffee -- I went directly to the site and asked there. It will control the valve, but not the pump.
> 
> A recent development is that the temperature seems to be noisy at times which causes the PID to get confused.


 @JeanDit and @EdsEspresso had long discussions about issues with steam operability, for example, this post wonders why the PID has such issues stopping the boiler at 125 vs. 100.



JeanDit said:


> Hello everyone, I made more testing, and the overheating problem only occurs when I use the steam button. Even if the steam option and cable of the MeCoffee is not plugged/use, it it still happening (otherwise, I would have simply used it for brew and move on). The brew temperature seems very stable. [...] IMO, it doesn't make sense that the PID is able to stop the boiler at 101 degree in a very stable way for the brew, and that it cannot do the same at 125 degree for the steam. From a software perspective, it is the same basic thing to do...


 In the first post of the German thread linked by @JeanDit



> After the PID no longer had the steam temperature under control (swing out like a normal thermostat), I lowered the temperature to be on the safe side.


 Recently @Daniel R provided a wonderful clear picture of the temperature sensor:

View attachment 45730


I've reviewed the data sheets, and the LM35DT does not seem to actually be rated for operation above 100C. It is confusing because some of the sensors in the LM35 family are, so the data sheet is confusing. However, the range is clearly indicated as 0-100C in the digi-key website and the UK Farnell website.

Here is the precise statement from the data sheet:









Here you can see how badly the error increases past the range of 100C (in fact, anything past this range is not even shown on the graph).









This makes me think that:



It is not absurd to believe that the severe issues noted by others regarding the steaming functionality are due to this.


Even at 100C, the sensor is being used nearly past its stated range of functionality, and the error on this temperature monitor are expected to be around 2deg at brew temperature.


*You should not be using the mecoffee PID in steam functionality mode. *


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