What's a cheap reliable way to sense 80C to 190C ? - Page 1
Forum section: electronics / beginners

author: Cliff Matthews
author_rank: Unknown
timestamp: March 04, 2021, 07:40:41 pm
content: Replacing a missing mechanical thermostat on an old heat press. I'll use a comparator to control the existing SSR and 1500 watt heater for regulating temps from 80 to 190C. I've tested various 10k ohm NTC's taken off heatsinks in ATX PSU's and resistance always becomes erratic past ~150C. I was thinking about crimping together some glass diode's next. I have lot's of old parts but it seems few idea's.

author: jesuscf
author_rank: Frequent Contributor
timestamp: March 04, 2021, 07:55:14 pm
content: Old good Thermocouple wire? You just need a difference amplifier to convert to voltage. The op-amp must have very small input offset; I've had good results with the OP-07. If you want to go fancy, add cold junction compensation. Lots of information on the web. Here is the link to application note AN844 from Microchip that could be useful.http://ww1.microchip.com/downloads/en/Appnotes/AN844-Simplified-Thermocouple-Analog-Solutions-DS0000844B.pdf

author: Gyro
author_rank: Super Contributor
timestamp: March 04, 2021, 08:10:39 pm
content: Yes, thermocouple or PT100 RTD, but thermocouple is cheaper.You could maybe try the thermistors sold for 3D printer heads - I don't know what they top out at?

author: floobydust
author_rank: Super Contributor
timestamp: March 04, 2021, 08:10:54 pm
content: At 190C you are past the limit for sensor plastics, wiring included. There areNTC thermistors in a glass diode package,good to 300C but need linearization. An Arduino can do the job then.For your time and money, why reinvent the thermostat. I would use a cheap REX-C100 kit with thermocouple, under $20 from eBay.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 04, 2021, 08:38:04 pm
content: Quote from: floobydust on March 04, 2021, 08:10:54 pmQuite agree, thanks! Ordering:https://www.ebay.ca/itm/REX-C100-Digital-PID-Thermostat-temperature-Controller-SSR-output-K-Thermocouple/164397486095Looks easy enough.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 04, 2021, 09:27:25 pm
content: The MAX31855 (analog) and MAX31856 (digital) are single chip TC amplifiers. You can choose the TC you want. SparkFun, Mikroelectronics, and Adafruit (maybe others) offer breakout boards with those chips. If you want analog, then of course, you would be using some sort of comparator.I have been using the MAX31856 for a few years. Works great.

author: jmelson
author_rank: Super Contributor
timestamp: March 05, 2021, 02:49:21 am
content: You can get thermocouple controllers on eBay for about $50, some even come with the thermocouple.I have used a couple of these.Jon

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 05, 2021, 08:34:31 am
content: buy encapsulated thermister with M3/4/5/6/8 (whatever you like and fits well) screw head, that's one pro approach, or some encapsulated thermocouple with any attachment type you likehttps://www.amazon.fr/DollaTek-Temp%C3%A9rature-3x10x1000mm-Thermocouple-Imprimante/dp/B08HQ5DX4R/ref=sr_1_11?__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=thermocouple&qid=1614933009&sr=8-11https://www.amazon.fr/TOPINCN-Thermocouple-Chauffage-Remplacement-Accessoires/dp/B07QYN6DQX/ref=sr_1_28?__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=thermocouple&qid=1614933009&sr=8-28https://www.amazon.fr/Max6675-thermocouple-Capteur-temp%C3%A9rature-Raspberry/dp/B06XCFKL2Q/ref=sr_1_37?__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=thermocouple&qid=1614933009&sr=8-37the links are for making example, buy from farnellor some pro sellerI prefer the screw-headed ones, just put some threaded hole in your plate and it's rock solidfor air temp sensing, buy simple thermocouple and leave it in the controlled air flow