# Digital Thermometer Errors



## fraser_john (24/9/07)

Ever since I automated my system using DS1820 I have always thought that the reading must have been slightly off, I figured it was just placement in the mash or elsewhere, but I just never seemed right. 

Finally, yesterday during a mash, I figued I would follow the probe around with a glass thermometer, which I had not calibrated. Looked to me like my DS1820 was reading at least 0.5C lower than it should have been and as high as 1.5C lower than the glass one.

I figure its really is reading wrong, I have often had problems getting my final gravity spot on and I guessed it may have been my attenuation, maybe not getting enough oxygen???? BUT, now I think that it might be generating too many unfermentables!!!!!! <_< 

Anyone else out there using the older DS1820 digital thermometers??? Have you upgraded to the DS18S20 and seen a better reading???

According to this document, the DS18S20 fixes the problems associated with the internal algorithm to determine temperature. 

View attachment ds1820_report.pdf


----------



## Roar! (24/9/07)

I read that the DS1820 could be as much as 3deg out after soldering, so I wouldn't use it. I use 18B20 on my home projects, pretty sure it has the same accuracy as the S version (0.5degC).

0.5deg is in spec even for the latest versions but if theyt are 1.5deg out one or both are wrong.

When you were taking readiung inthe mash were the sensors very close together, and did they have time to stabilise the readings? I am a K+K brewer so I am not sure what the mash process is, but if that means boiling maybe one and not the other was affected by hot currents of water in the mash?

You can do a cheap easy calibration for 0deg using lots of ice in acontainer of water. Mix it well and see what they both read. For 100deg boil a pot of water.

What equipment are you using to read it?


----------



## Aaron (24/9/07)

That document indicates you should get +or- .5C. That assumes a calibrated device though. I couldn't find where it said how often the device needed to be calibrated or how, though I only had a quick scan through it. I think the ice and boiling water will be a little ambiguous if you are aiming for a + or - .5C accuracy. If you are serious about hitting your temps that accurately I would get it professionally calibrated.

Personally I don't go to that level but I'm not willing to spend the money on regular calibration. Quality measuring equipment is little better than the cheap stuff without regular calibration.


----------



## fraser_john (25/9/07)

Roar! said:


> I read that the DS1820 could be as much as 3deg out after soldering, so I wouldn't use it. I use 18B20 on my home projects, pretty sure it has the same accuracy as the S version (0.5degC).
> 
> 0.5deg is in spec even for the latest versions but if theyt are 1.5deg out one or both are wrong.
> 
> ...



When comparing the glass thermometer with the DS1820, they were right next to each other in the mash. I use a purchased USB device that reads upto 250 odd DS18x20 devices.

I have ordered a half dozen DS18S20 units and will replace the DS1820 ASAP. In the meantime I am going to do the ice/water trick and compare both the glass and digital ones. I can quite easily add some VB code to allow for a fixed difference, but if its variable depending on actual temperature......it would be hard.


----------

