I've used RTDs for some time because I want all my sensors interchangeable. That worked well until I bought Chinese probes. They had very good sensor elements, but... the cable terminated the sense wire to the drive wire in the end connector. Only 2 pins were live in the 4 pin connector. That caused both inaccurate and varying readings. I disassembled the cable end and probe body and carried all three wires into the probe and connected the drive & sense wires there. Much better.
The probes you have look very similar to the ones I got two years ago including the unusual connectors.
Do you have to modify your probes or does your source properly wire them? Either way, getting correctly wired ones from you sounds like a way to save a really annoying task of disassembly, soldering, and reassembly...
The Chinese sensors also had the RTD chip suspended in air at the end of the body. The response time was very, very slow. The other mod I made was to put a small quantity of >electrically insulating< heat sink compound in the end of the probe such that there was a solid thermal connection between the sensor element and the case. That made the probe respond about 10 times faster. It appears that silicone grease & zinc oxide don't affect the RTD element, at least over the last year.
I made 0.01% 100 & 143 ohm test plugs which really help figuring out problems. The chip resistors only cost $3 and the plugs $5. Well worth it.
You've made a very interesting design for your brewing system! It solves quite a few problems I've been worrying about.
Joined: 04 May 2018 Posts: 11 Location: SF Bay Area
Link Posted: Mon Apr 01, 2019 1:54 am Post subject: Re: RTD probes - stock or modified?
Curious how you did this?
I disassembled the cable end and probe body and carried all three wires into the probe and connected the drive & sense wires there. Much better.
Did you just connect two of the pins on the inside of the probe? Did you notice any difference in the temperature or temperature stabilization? I was under the impression that the slow temperature stabilization was more of a function of PID/RTD controller, rather than the probes, since--correct or not--the PID just senses the resistance between the 3 wires.
I was also under the impression that all of the RTD probes that are typically used for home breweries (2-pin, 3-pin and 4-pin) only use two of the pins, and two of the wires are shorted together at the RTD plug. Definitely true of the 2-pin and 4-pin (the two types that I have). Isn't that true of the 3-pin also?
Joined: 12 Dec 2010 Posts: 10680 Location: Ottawa, Canada
Drinking: German Lager, Electric Creamsicle, London Pride, Kolsch, Belgian IPA, Red IPA, Russian Imperial Stout, Black Butte Porter
Working on: Weizen, Belgian Quad, Wit, English Pub Ale, Electric Creamsicle
Link Posted: Sat Apr 27, 2019 1:56 pm Post subject: Re: RTD probes - stock or modified?
I noticed something else from the original poster that I thought I'd comment on:
I've used RTDs for some time because I want all my sensors interchangeable.
With any probe (be it RTD/Pt100, K-type/TC) they will all have slight offsets in readings. That is why most PIDs (including the ones we sell, use, and recommend in our build instructions) come with an offset value so that you can adjust for this. What this means is that while using all the same probes in a setup allows them to be interchangeable, you can't simply switch between probes quickly with a switch or similar because the reading may be off slightly for one of the two. To make it accurate you'd also have to go in to the PID and change the offset value. This is why, generally speaking you should have one temperature probe per device that is using that reading.
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