Ntc Ss Probe

[skippy]

I suspect that the Fridgemate NTC SS Probe (one you can immerse in wort), is not as accurate as the original probe that is supplied with the Fridgemate - due to the NTC probes sheer size/inertia!

Brought a digital stick therm. from T@@@y for $30, and have currently four 25L fermentors in my two shelf converted fridge (which is monitored by the Fridgemate - with NTC SS probe in fermentors)

Every day throughout day, I record the temps of all fermentors by immersing NTC SS probe in each of the liquids (2-3 min), then check temp in fermentors with stick therm (from T@@@y) and original probe that comes with Fridgemate (2-3 min immersion time).

I have concluded that the NTC probe on my Fridgemate needs correction of + or - 1 degree C (as Fridgemate does not measure increments of 1/2 a degree).

 

[bill_gill85]

I don't think it has to do with size or inertia, but as the temperature probe is a NTC device (Negative Temperature Coefficient) it may not have the exact same sensor type as the original sensor. I checked my probe on a multimeter & it has a different measured resistance to the sensor at ambient temperature. I have not attempted to calibrate the probe to sensor (by inserting a resistor in series with the sensor) as the two devices may have a different temperature coefficient. Personally, I plan on setting the fridgemate using an external thermometer as my reference, noting the temperature offset of each sensor.

Ben

 

[therook]

I suspect that the Fridgemate NTC SS Probe (one you can immerse in wort), is not as accurate as the original probe that is supplied with the Fridgemate - due to the NTC probes sheer size/inertia!

Brought a digital stick therm. from T@@@y for $30, and have currently four 25L fermentors in my two shelf converted fridge (which is monitored by the Fridgemate - with NTC SS probe in fermentors)

Every day throughout day, I record the temps of all fermentors by immersing NTC SS probe in each of the liquids (2-3 min), then check temp in fermentors with stick therm (from T@@@y) and original probe that comes with Fridgemate (2-3 min immersion time).

I have concluded that the NTC probe on my Fridgemate needs correction of + or - 1 degree C (as Fridgemate does not measure increments of 1/2 a degree).

Skippy,

How accurate is the stick thermometer?

Rook

 

[Thirsty Boy]

It could have a bit to do with the resolution of the readout..

I dont have a fridgemate, but I do run a couple of PIDs. They think in 0.1 increments but they only display whole degrees. So the temperature might be sitting on 17.6 but its still reading 18 and would right up to 18.5

thats about a degree swing. might be contributing to the difference you see. Kind of like digital parallax

Thirsty

 

[hando]

Thirsty - A digital parallax eh? :huh:

 

[bill_gill85]

I wouldn't so much say digital parallax, yes the ADC could be between values, which is more than likely a sensitivity error. I will treat my fridgemate more like a thermostat than a thermometer. I expect that the SS probe contains a different thermistor to the original probe, leading to either a calibration offset or possibly a completly different co-efficient, making 1C increments actually 0.9C or 1.05C meaning that the whole scale is lost & external calibration by an accurate themometer is required. Its basically a correction scale for a thermometer similar to that for a hydrometer. There are better sensors available (ie Dallas Semi DS18B20), but for homebrewing the probe is adequate provided you have the right attitude towards its operation.

 

[oldbugman]

There are better sensors available (ie Dallas Semi DS18B20)

20k NTC sensor are more than accurate enough for most temperature applications and definitely more than enough for fermentation.

--edit speeling --