Temperature based on/off schematic

[RadRacer]

I'm trying to design a schematic that will be on when one temperature A is higher than temperature B, and will turn off when A reaches B or is below. I need the output to drive a 12V relay; I was thinking some LM34's hooked to a LM393, but not sure where to go from here. I know I'm probably gonna need an op-amp to raise the output of the comparator. I wouldn't mind being able to adjust the difference between the two before the relay is activated; for instance, change it from temperature A being 10* higher will turn it on, but then the next day I could adjust it so 30* will allow it to turn on. I imagine a pot would allow this, but I'm not quite sure how the ouput is from the LM34s. TIA everyone

 

[ericgibbs]

I'm trying to design a schematic that will be on when one temperature A is higher than temperature B, and will turn on when A reaches B or is below. I need the output to drive a 12V relay; I was thinking some LM34's hooked to a LM393, but not sure where to go from here.

hi,
What are the tempr ranges.?

 

[RadRacer]

hi,
What are the tempr ranges.?

Ranges are gonna vary; I'm using it to control a solenoid for an intercooler sprayer on my car. Temperature B will be the ambient air temperature, and Temperature A will be the intercooler temperature. Ambient air varies from 10*F to 95*F here in FL, and the intercooler temp will vary from 0*F to 130*F

 

[ericgibbs]

Ranges are gonna vary; I'm using it to control a solenoid for an intercooler sprayer on my car. Temperature B will be the ambient air temperature, and Temperature A will be the intercooler temperature. Ambient air varies from 10*F to 95*F here in FL, and the intercooler temp will vary from 0*F to 130*F

hi,
I am drawing a circuit, do you really means this... will be on when one temperature A is higher than temperature B, and will turn on when A reaches B or is below. ??

Im not sure I follow. ???

 

[RadRacer]

hi,
I am drawing a circuit, do you really means this... will be on when one temperature A is higher than temperature B, and will turn on when A reaches B or is below. ??

Im not sure I follow. ???

I apologize, it should be will turn off when temperature A reaches temperature B

Example: temp A is 80 and temp B is 70. This will cause an output to be on. Once temp A lowers to 70 or below, the output should be off

 

[ericgibbs]

I apologize, it should be will turn off when temperature A reaches temperature B

Example: temp A is 80 and temp B is 70. This will cause an output to be on. Once temp A lowers to 70 or below, the output should be off

hi,
A circuit as simple as this will give Ta > Tb = Relay ON.

Do you follow it OK.? Ta and Tb are your LM34a and LM34b

 

[RadRacer]

Thanks! I have a few questions though: I can't seem to locate resistors 3, 5, and 6, or transistor 1 in your schematic. Is R2 to simulate the solenoid, or do I need it in series with the solenoid? Also, u2 is from the 393 comparator, correct? Sorry, I haven't done any schematics in years

 

[ericgibbs]

Thanks! I have a few questions though: I can't seem to locate resistors 3, 5, and 6, or transistor 1 in your schematic. Is R2 to simulate the solenoid, or do I need it in series with the solenoid? Also, u2 is from the 393 comparator, correct? Sorry, I haven't done any schematics in years

hi,
R2 represents the solenoid. You didnt tell me the specification.

The reason for missing component names is because this is a cut down version of a similar controller.

Note , in a LM393 there are two comparators.

 

[RadRacer]

hi,
R2 represents the solenoid. You didnt tell me the specification.

The reason for missing component names is because this is a cut down version of a similar controller.

Note , in a LM393 there are two comparators.

OK, thanks for clearing that up. One last thing: is R4 meant to be a 4.7K Resistor? If not, what do you mean by 4k7

 

[ericgibbs]

OK, thanks for clearing that up. One last thing: is R4 meant to be a 4.7K Resistor? If not, what do you mean by 4k7

OK.
The K suffix is now often used as the decimal point,, 4.7K aka 4K7, also a 1.5R is often marked as 1R5

 

[RadRacer]

OK, thanks. I just ordered everything. I made a few small changes (just master on/off rocker, and a push-button to bypass the temperature sensors in case I want it on when the temps aren't in the range), but will let you know how it works. Thanks for the help!

 

[ericgibbs]

OK, thanks. I just ordered everything. I made a few small changes (just master on/off rocker, and a push-button to bypass the temperature sensors in case I want it on when the temps aren't in the range), but will let you know how it works. Thanks for the help!

hi,
Are you OK in connecting the LM34's.??
Look at the datasheet and use the circuit in this image.

 

[RadRacer]

Yes, pretty sure I understand it. The V-out goes to the 10K resistor and then the comparator. Vs and ground go to power and ground, respectively. Also, I purchased LM35's instead. The schematic, shouldn't change any, right? My understanding was the only difference is the scale being used; LM34 is Fahrenheit, while LM35 is Celsius

 

[ericgibbs]

Yes, pretty sure I understand it. The V-out goes to the 10K resistor and then the comparator. Vs and ground go to power and ground, respectively. Also, I purchased LM35's instead. The schematic, shouldn't change any, right? My understanding was the only difference is the scale being used; LM34 is Fahrenheit, while LM35 is Celsius

Hi,
Dont let your fellow country men hear that you are going Metric.!

Yes its the same spec as LM34,,, if you mount them remote from the circuit and get 'noise' problems, use this image.

 

[RadRacer]

Hi,
Dont let your fellow country men hear that you are going Metric.!

Yes its the same spec as LM34,,, if you mount them remote from the circuit and get 'noise' problems, use this image.

lol, the only reason I picked them over the LM34's is the site I bought everything from only has the LM35's in stock. I'd much rather buy everything from one place, and since they operate the same and I won't actually be reading the temperature, I didn't see a problem. And thanks for the filter schematic. They will be remote from the circuit, so no telling if I'll need that or not. Hopefully I won't, but inside an engine bay, I have a feeling I might