Thermocouple amplifier

[Lukas060606]

Hi,

It's me again. Anyone have any experience with these AD8495 amplifiers? I was going to buy the AD595's since they are mentioned in quite a few posts here, but the 8495's are a lot less expensive. They look like they are a newer product, and I was wondering if there were any significant pros/cons. As always, any input is greatly appreciated.

 

[jebatty]

I believe that, without additional circuitry, the 8495 is spec'd for 0-50C. The 8497 is spec'd for 25-100C.

 

[Lukas060606]

That is at the reference point, correct? Unless I'm missing something (which is easy for me to do with this stuff), the spec sheet says the reference temp is optimized at 25C, or 77F. I'm going to mount this circuit low in the room, and I do not think the 8495 is going to get up to even that temperature. The measurement junction is going in my flue, so those temps are much higher. Am I good, or am I off base?

 

[Lukas060606]

On further reflection, I think I'll go with the more expensive 595's. The 8495's are surface mount, and my soldering abilities are not quite there. In this instance, more money = less frustration.

 

[Nofossil]

I use the 595 chips. They work really well, but I learned the hard way that you need bypass caps across both the power supply leads as well as between pins 10 and 11.

 

[Lukas060606]

Thanks nofo. After reading a bunch of your posts recently, I was planning on taking the "cap the crap out of it" approach. Have any cap sizes/configurations worked best for you? Also, what are you using in your storage tanks for temperature readings? I was thinking thermistors for mine.

 

[Nofossil]

Thanks nofo. After reading a bunch of your posts recently, I was planning on taking the "cap the crap out of it" approach. Have any cap sizes/configurations worked best for you? Also, what are you using in your storage tanks for temperature readings? I was thinking thermistors for mine.

I used .1uF ceramic caps - 1 across the power pins and one between 10 and 11.

I used thermistors in my storage, in part because they're really small so I could get three of them with associated wires down inside a small diameter piece of soft copper. If you use them, be prepared to deal with linearizing the output - they're really nonlinear.