[DennisCNC]

Has any one seen a circuit that will sence 2mV to 150mV using a lm3914 or similar chip to drive leds in dot mode?

Or can chip do that with out any other additions?

Thanks

[ViperTX]

Well generally noise levels are more then that.....why don't you give us more info...

[DennisCNC]

I'm just try to make a simple high temperature termostat ~1100 F using a thermocouple and since it makes a voltage based on temperature I was thinking I can use it to drive the leds outs and connect them to relays as needed.

[Al_The_Man]

You could maybe try it direct coupled, but you may need a linear opamp to scale it if neccessary, You can get info and a nice set of free books from Omega.com on thermocouples etc.
Al.

[pminmo]

You are aware you have to treat the dissimilar metals of the thermocouple with compensation circuits for the copper to xxx metal of the thermoucouple leads?

[gar]

060317-2008 EST USA

DennisCNC:

I would suggest an op amp, and from its output a meter to read temperature, and threshold detector with hystersis to control your on-off relay.

See the following site figure 16 for calibration information. At your temperature there is probably no need for cold junction compensation. Of course it depends upon the accuracy you want.

Relatively speaking you do not need fast response and therefore you can add substantial filtering on the thermocouple output.

The conversion from F to C is --- C = (F - 32) 5/9 . This you can derive from 0 C = 32 F and 100 C = 212 F, and knowing you have a linear relationship.

http://www.omega.com/temperature/Z/pdf/z021-032.pdf

.

[DennisCNC]

This will be for a aluminum smelter so +/- 150deg. will be ok.

gar:

I like that PDF!!