Talk about FAST temperature sensors. I worked on a medical instrument many years ago. I made a test machine based on a PC and software in Pascal that dipped the thermistors in ice water. The thermal time constant had to be 20 - 40 mS to work in the final application. Resistance went to 66% of final temperature in less than .04s! Some were thrown out because they were too fast. This was a very special thermistor made for us by Thermometrics (NJ , I think). It also had to meet low leakage and a high voltage spec. They are still going and will custom make you a special themistor if needed. They will help you specify your part so it always meets a certain accuracy under specified conditions. Mike ----- Original Message ----- From: "PicDude" To: Sent: Sunday, June 29, 2008 7:14 AM Subject: Re: [EE] Fast temp sensor? > > Lots learned a lot over the past few days, and it really does seem that > thermocouples (especially open-elements) are very very fast. Type T > thermocouples are apparently the most accurate and available in two > classes, > with 0.5 deg-C error versions commonly available. But thermocouples need > a > lot (relatively) of support circuitry, especially since this is in an > automotive application (measuring air temp at a couple points in the > intake > tract). 1sec to 2sec works fine, since this is a monitoring application, > and 1% error would be nice, although a bit more would still be acceptable. > > Mounting (for the end-user) will be a major factor as well, so any basic > element/component that needs to be PCB-mounted becomes less desirable, as > I'd have to factor in the labor cost to build those to a user-friendly > format ... and that's still be decided upon. > > I had missed the graphs with response time in those datasheets (LM35 > etc) -- > I was looking for electrical parameters. But checking back now, they're > relatively quite slow. I found RTD's that are available in better than 1 > sec response time using open elements, and they require minimal support > circuitry. They also come mounted to a stem/flange/etc so end-user > install > is ready-to go. The problem is cost -- so far they're in the $35-$40 > price > range each (in 50-100pc quantities). > > I always thought that thermistors were not-so-accurate, but I've been > corrected again it seems. I'm looking at various datasheets now in the > 0.5% > to 1% range, and they seem promising. Very low cost (<$1 ), and I'm > working > out a mounting structure to see just how much it would cost if assembled > in-house. I also found some suppliers of thermistors in flanged probes, > so > I have some calls to make this week. > > Thanks, > -Neil. > > > > -- > View this message in context: > http://www.nabble.com/Fast-temp-sensor--tp18104658p18181248.html > Sent from the PIC - [EE] mailing list archive at Nabble.com. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist