Electronic – the fastest temperature sensor?


I'm making a Sous Vide using Arduino with a DS18B20 temperature sensor. My problem is that the DS18B20 reacts too slowly to temperature changes. For example, if you take it from ice water (1°C) to boiling water (100°C), DS18B20 takes a full minute to reach 95°C. Worse, the temperature show asymptotic convergence; near final temp, DS18B20 approach at like 7sec/°C.

So, what is the fastest temperature sensor available today (and cheap) ?

Best Answer

1 minute to reach 95% is incredibly slow. Something must be wrong with your sensor. It's just not possible for a TO-92 alone to have such a slow response.

In this Texas Instruments Datasheet for an LM34 (or LM35) in a TO92 package, they give a graph of thermal response in a stirred oil bath, which should be quite similar to your situation:
LM34 TO92 thermal constant

So in a liquid it will reach 95% in less than ten seconds.

Perhaps you're using a waterproof DS18B20, and it's not thermally connected to the walls of the stainless steel tube. The shiny tube, and thin layer of air, will form quite a good insulator.

DS18B20 waterproof from AdaFruit

They say

  • Stainless steel tube 6mm diameter by 30mm long
  • Cable is 36" long / 91cm, 4mm diameter
  • Contains DS18B20 temperature sensor

So the problem isn't the sensor itself, it's the packaging, which is something you have to solve no matter what sensor you use. The DS18B20 is a great little sensor, mainly because it is reasonably accurately calibrated at the factory. Any more analogue sensor - thermocouples and thermistors, will need special care to calibrate to better than a couple of degrees C.

Try this again with a bare sensor, in a heatshrink tube or a blob of epoxy, or take it apart and fill the tube with oil or glue to improve the thermal conduction to the device.

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