# schmitt trigger

Discussion in 'Homework Help' started by mndewa, Oct 17, 2012.

1. ### mndewa Thread Starter New Member

Sep 16, 2012
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A thermocouple circuit produces an amplified voltage difference of 0.5V when there is a change in temperature of 10°C.Thermocouple amplified voltage at 30°C is 2.5V.The thermocouple circuit is to be used as a temperature sensor to maintain an oven temperature between 40°C and 80°C by switching ON and OFF the power supply to the oven.The oven is to be controlled by schmitt trigger in connection with the thermocouple circuit.The schmitt trigger is to be connected to ±15V.
(a) Determine schmitt trigger voltage levels (upper and lower trigger level)
(b)Sketch hysteresis loop and show all necessary voltage levels
(c)draw the schmitttrigger circuit and determine reference voltage

2. ### Dodgydave AAC Fanatic!

Jun 22, 2012
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your thermocouple output is not linear, at 10C its 0.5v, yet at 30C its 2.5v, it should be 1.5v at 30C?

3. ### mndewa Thread Starter New Member

Sep 16, 2012
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0
It's ok, help me to solve it

4. ### Dodgydave AAC Fanatic!

Jun 22, 2012
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772
if you want help, then show us what you get so far?

5. ### WBahn Moderator

Mar 31, 2012
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It's not ok. If it is nonlinear, then knowing what the voltage is at 10C and 30C is not enough information for us to determine what it is at 40C and 80C.

It's also not ok since you haven't shown any effort to solve it yourself. Show what you have done thus far and where you are having problems and we will help guide you back to the right path. And, please, don't just say that you don't know were to start.

6. ### Ron H AAC Fanatic!

Apr 14, 2005
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The statement was:
Note the word "change".

7. ### WBahn Moderator

Mar 31, 2012
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IMHO, the english is not good enough to base interpretation on which specific words were used. I took "change" to mean a difference between the sense point and the reference point.

But if that isn't what it means, what is the "change" relative to? And what is the 30C referring to?

8. ### Ron H AAC Fanatic!

Apr 14, 2005
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I see it as a data point (2.5V@30°) and a slope (0.5V/10°). (We do have to assume a sign for the slope, which was an omission by the instructor.) From this we can deduce:

V=0.05*T + 1

From this equation you can find the voltages at 40° and at 80°. Design a Schmitt trigger with these threshold voltages.

Last edited: Oct 21, 2012
9. ### WBahn Moderator

Mar 31, 2012
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I can see where that is a reasonable interpretation. Hopefully the OP will confirm it.

10. ### mndewa Thread Starter New Member

Sep 16, 2012
7
0
Thanks, but how did you get that equation? show me clearly.
give me the link where to find tutorial

11. ### mndewa Thread Starter New Member

Sep 16, 2012
7
0
where can i get tutorial about that question?

12. ### Ron H AAC Fanatic!

Apr 14, 2005
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657
I'm pretty sure I learned how to derive an equation from a graph in high school.
Attached is a graph that should explain how to do it.

Also, Google "derive equation from graph".

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13. ### mndewa Thread Starter New Member

Sep 16, 2012
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0
thanks, but where can i get tutorial?

14. ### WBahn Moderator

Mar 31, 2012
18,088
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A tutorial on WHAT?

That exact specific question? I'm sure it's out of print.

Determining the equation of a line from a point and the slope? Google "equation of line from a point and the slope"

How thermocouples work? Google "How thermocouples work"

What a Schmitt trigger is? Google "Schmitt trigger"

Do you see a pattern, here?

Now, if you want to present your efforts, it will give us something to work with. But as long as you just keep posting "give me, give me" demands, you won't get much in return.