600 degree celcius temp. measure....

M

msd

New Member

• Jan 2, 2010

• #1

I am trying to make control heater for particular temperature more than 500 degree celcius....I want to know which is the best way to measure this....using thermocouple type-k....which amplifier would be best for amplifying signal from type-k thermocouple....
I heard about ad-595....but it requires higher supply for more than 300 C ....any best way to do this....
Type-k table for temp. v/s voltage..
https://srdata.nist.gov/its90/download/type_k.tab
https://www.electro-tech-online.com/custompdfs/2010/01/emfk_c.pdf

by seeing voltage level I will need atleast gain=100 for good resolution...

 

Last edited: Jan 2, 2010

dknguyen

Well-Known Member

Most Helpful Member

• Jan 2, 2010

• #2

Where does it say that the AD595 requires dual supply for high temperatures? It requires dual supply for sub-zero temperatures. But you just need a higher +V for high temperatures. THermocouple is the best way for temperatures like that and the AD595 is pretty much the whole solution...another one is the AD597 which is calibrated to work in more optimally higher tempeture environments (ie. very near the oven where it would be warmer than ambient).

 

Last edited: Jan 2, 2010

M

msd

New Member

• Jan 2, 2010

• #3

ya...I made a mistake in reading....but any other chip to do job...its expensive....

 

dknguyen

Well-Known Member

Most Helpful Member

• Jan 2, 2010

• #4

well there is the MAX6675. It only accepts up to 5V though so it can't reach the temperature you want. Between these 3 ICs, I know of no others. You can get the AD597 in a much cheaper SOIC-8 packaging though. That's the reason the MAX6675 is also a lot cheaper, and why the AD595 is so expensive (it doesn't come in a cheap plastic IC package).

http://search.digikey.com/scripts/D...T.z_homepage_link=hp_go_button&KeyWords=AD597

 

Last edited: Jan 2, 2010

MikeMl

Well-Known Member

Most Helpful Member

• Jan 2, 2010

• #5

How much precision do you need? If you have a separate method of MEASURING the actual temperature of what you are heating, then the amplifier that amplifies the thermocouple just for the controller doesn't have to be anything special. If it has a few mV of offset, that wont effect the final temperature, which you will be turning a pot to set anyway... I have done this with a very simplistic opamp.

 

M

msd

New Member

• Jan 5, 2010

• #6

precision is not a problem...I just wanted to make thermal switch for a particular set temperature but in higher temperature ranges..(500-700 C)..so my idea is to turn on and turn off the heater around set temperature....

 

MikeMl

Well-Known Member

Most Helpful Member

• Jan 5, 2010

• #7

So, just a TC amplified by an ordinary opamp, fed to a comparator to switch a transistor/FET, which switches a relay, which switches the AC power On/OFF to the heater would work?
The Transistor/FET and relay could be replaced by an SSR.

 

M

msd

New Member

• Jan 5, 2010

• #8

Mike...
By using comparator-relay in comparator mode...don't you think relay will be on/off frequently which can lessen its lifetime...because comparator voltage will be precise and at that point relay will operate around it...so is there a way to set a littel tolerance band so it operates in range rather than a point...to reduce relay operation...
for example if I set t=500 C then I want it such a way that I have a bandgap of 5 degree so relay operates at 505 and 495 ...id it possible without uC...

can you suggest any ordinary amp. which can give good amplification in this case......

 

Last edited: Jan 5, 2010

MikeMl

Well-Known Member

Most Helpful Member

• Jan 5, 2010

• #9

Sure, just use a little positive feedback around the comparator to make a small hysteresis deadband.

Attachment is from previous post on this very topic...

 

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• Hysteresis.png

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M

msd

New Member

• Jan 5, 2010

• #10

it indicates I need to try out different feedback values to adjust deadband........

 

MikeMl

Well-Known Member

Most Helpful Member

• Jan 5, 2010

• #11

Yes, consider R4 and R5 as a voltage divider. Note the ratio of R5 to R4. Start with R5 very big (~2megΩ), and keep reducing it until the chatter goes away, or you have your desired hysteresis.