alternativessensortemperaturethermistor
I am in need of a thermistor with characteristics, such as those of now discontinued KTY84-130 (link to datasheet). I am after the exceptional linearity it features and also temperature range, up to ~ 250-300 °C. Its low price was also a plus.
How do I find out what's a good replacement thermistor I could use instead?
For reference, here is the schematic you supplied that we will be discussing:
There are many things wrong here:
I'm guessing the most likely cause of your symptoms is you have the gain pot cranked to invalidly high gain, so the output is small input offset errors amplified. These can come and go and possibly oscillate as different parts of the chip heat or cool slightly from other parts of the chip.
Fix all the things mentioned above before coming back with more questions. Next time I won't be as forgiving of obvious sloppiness and bad schematic drawing. When you are presenting things to others, it's your job to present them clearly and neatly else risk being dismissed as a waste of time.
You have now revised your schematic:
This looks like a more reasonable bridge circuit, but you still haven't fixed the basic problem of possibly having invalid gain. I don't like having to repeat myself. Replace VR2 with a fixed resistor, or leave it off to get unity gain for initial debugging.
With a reasonable value for VR2, you should be able to vary VR1 and watch the output go up and down over part of the range of VR1. When VR1 is close to the value of RT1, the two inamp inputs will be close to the same value. If REF is tied to ground, then you'll be right at the edge of a output response. It would make more sense to tie REF to 2.5 V so that the output is at mid range when RT1 equals VR1. You should then be able to see the output go up and down as you heat and cool RT1.
Maker and model specifications for your particular battery will state the range and the cutoff temperature for the thermal fuse which is mandatory in all 18650s sold in the US, that is probably the ultimate limit and I think it's 87-95'C. Today some batteries like Panasonic have very good PTC, you can short them from 4.4 volts and they are messed up but in one piece.
Battery shops generally specify a discharge temperature of -10 to 60'C and a charge of 0-45'C for 18650's, although charging under 10 degrees does not help lifespan, and will kill a bad battery.
different batteries get too hot at different output currents. Some batteries have temperature protection which switches off the battery above a certain temperature.
Some crazy people test their batteries to see the output performance, and dangerous temperatures:
Best Answer
Low Cost, High resistance semiconductor thermal sensors at 300'C appear to be going off the market for various reasons. Reliability being foremost.
Another e.g. http://www.digikey.com/product-detail/en/nxp-semiconductors/KTY84-130,113/568-3254-2-ND/1068979
Thin Film Platinum Resistor technology appears to be the best for automotive low cost, fast response, high-rel for EGR and other applications. Up to 300'C
e.g. http://sensata.com/sensors/automotive-sensor-darts500-e.htm Custom parts are avail, if you have high volume demand.
If your volume is low with multiple sensors used, thermocouple wire and shared electronics could be an option or remote IR detection of heat radiation.