What I did with the first sodium chlorate cell (last Summer), was to use a 1/4" PVDF compression fitting and filled the gaps with a slit piece of silicone tubing. When I tightened the ferrule, the silicone squeezed tight around the leads and sealed them. Say what you will but it worked.
If you need to use shrink tube, use either PTFE or PVDF shrink tube, especially if it needs to come in contact with the electrolyte. It's available on eBay from China for a "reasonable" (some more than others) cost. It does require higher heat to shrink it, which may cause problems with lower melting point insulation on the sensor leads.
With the PTFE coated PT100 sensors, I don't see a problem, but the split silicone tubing trick might be all you need to do to seal it in the compression fitting.
One question though, are you using the temperature controller just as a temperature display or are you using it to control the temperature of your cell?
Good luck and please share your experiences.
I like that, it's really simple but would work quite nicely! Your idea also has me thinking.. To seal my lid I made my own silicone o-rings that fit into a groove in my lid like this:
I made my o-ring by cutting a groove in HDPE plastic and filling it with silicone. Silicone doesn't bond to HDPE, so with some care I was able to remove it intact. I wonder if I could make a much smaller one and if it would work to seal my temperature sensor...
I'll more than likely be using it just as a display initially and adjust things manually if I want to regulate the temperature. I did also purchased a solid-state relay that I may use to power a heating element if it's not running hot enough. However, these cells seem to run quite warm even without insulation, so if I decide to run it warmer I think I'd start with insulation. I may need to cool my cell rather than heat it so I might end up using my controller to operate a fan or small pump- though I'm not overly familiar with solid-state relays, so I'll have to read up on them first regarding their ability to operate inductive loads.
I'm still fairly interested to know how well my heat shrink tubing will hold up to the conditions of the cell so I may involve some somewhere (even just around an electrode) to test it.
For a Cell with a thin Cell material, you can use your sensor mounted at the outside, when you ensure its well insulated.
Another good way is, to take a 10x8mm PTFE Tube and a 8x6mm Boro. Glass tube.
A 5mm sensor will fit in well and with thermal sealing you can seal one side of your glass tube and putting it into the PTFE tube to make a thightly seal.
Unfortunately i've only got one picture of it, since the small boro tube has broken when i disassembled the cell the last time.
Between the right Cathode and the Anode you can see the small diffusor-tube for the HCL and in the front the Tube for the Temperatur sensor.
I placed a temperature sensor on the outside of my cell the last time I ran it. I didn't insulate it though, and once I thought of it I didn't want to because I figured it would render my initial temperature readings irrelevant. I may do it in the future though in case I want to know the temperature in multiple locations to see if the temperature is uniform.
Did you get any salt creep coming through in between the boro. glass and the PTFE tubing?
Thanks for the suggestions, WSM and PTFE, I'll be sure to post how things go!