For some time I’ve been using the DS18B20 to measure boiler temperature, but decided to upgrade to the TSIC 306 which has a wider temperature range and faster update rate.
The TSIC 306 is a fairly small TO92 package (about 4.5mm wide, 2.2mm thick and 4mm high) so I decided to try encapsulating it in an M4 hex M/4 spacer (as suggested here). This worked out pretty well, as shown below, pictured alongside the original thermostat from the Gaggia Classic.
The spacer is M4 Aluminium, 20mm high, 7mm across faces, male to female (Richco HTSA-M4-20-2, Farnell 1898535). The male thread has been filed down to about 6mm length, to match the existing thermostat.
I drilled out the female thread in the spacer with a 4.5mm bit to 15mm depth, filled with heat transfer compound and pushed the sensor deep into the spacer. The three sensor leads are individually insulated with heat shrink tubing, and more heat shrink is used to encapsulate the cable and sensor.
Aluminium has excellent thermal conductivity, and simply touching the case with a fingertip is enough to trigger an immediate change in temperature reading!
The only awkward part was fitting it into the boiler. I wasn’t able to do this in situ, but had to remove the steam wand and knob, unscrew the four allen bolts around the group to free the boiler. This allowed enough freedom to tilt and move the boiler slightly to the right, so that I could screw in the sensor by hand.
The new sensor is up and running on the machine, and I’ve left the DS18B20 installed in parallel, so I can compare performance.