[SOLVED] Analog Circuit noise problem

[romel_emperado]

Im also puzzled why there is a transistor circuit before the regulator... I have a feeling that is one cause of the problem. and as a result due to low voltage if the relay turns on then the reading of adc in the first place will be affected..

 

[Sajjadkhan]

He put it for 24V down to 12V and then 5V so the regulator wont heat up....i strongly believe he should replace the resistor.

 

[romel_emperado]

yes.. replacing the resistor might do to give more current to the base of the transistor.. but he can easily remove the the transistor and use 9v -12v transformer if he is avoiding heat up.. put heat sink to draw hear away hehe..

 

[Sajjadkhan]

Yea i already told him that but the circuit is to be put in fryer which has its built in 24v supply. I think his teacher gave him this circuit to learn something.

So my conclusion is its not a noise problem rather its a "not supplying enough current" problem.

 

[romel_emperado]

So my conclusion is its not a noise problem rather its a "not supplying enough current" problem.

I believe this..

I made a circuit before with not less than 6 relays but there is no weird thing happen like this..

I separated the supply for relay and the ucontroller but all are common ground...

 

[lloydi12345]

Thanks for your concerns Sajjadkhan and romel_emparado. I've just measured the resistor and it was 15k. I guess the design layout passed to me was really old. It was written on the layout that it is 100k. I did your advice placing 1k resistor 1W in parallel with the 15k and the resistor quite heats. The total resistance now is 937 ohms. I'm waiting for the circuit to fluctuate again. I'm glad that there are people here really concerned to people who needs lot of help.

 

[romel_emperado]

let us know the result

 

[Sajjadkhan]

Did you measured the R29 after removing it? otherwise it would be in parallel to other circuits. 630 ohms is the exact value indeed but 1K should show improvements. Use a high watt resistor and it wont heat up.

 

[lloydi12345]

let us know the result

I will. Thanks.

Did you measured the R29 after removing it? otherwise it would be in parallel to other circuits. 630 ohms is the exact value indeed but 1K should show improvements. Use a high watt resistor and it wont heat up.

Yes, R29 is 15k 1/2W. The soft copy given to be must be outdated. I didn't removed R29 instead I attached 1k ohms 1W parallel to it. Their total resistance now is 937 ohms. 1k heats up but not in a boiling point (I can touch it until 15 sec only)while the 15k resistor is not hot.

From 323 deg it switched one time to 324 then suddenly went back to 323. I'm still checking its performance now and hoping for some improvements. Thanks.

 

[Sajjadkhan]

From 323 deg it switched to 324 then suddenly went back to 323.

1 or 2 bit errors are normal, yea for that you can use averaging.

 

[lloydi12345]

Sajjadkhan this is already using averaging method. As what I've said, after shorting the two grounds, the error jumps decreased to 1 degrees that's why I hesitated to remove the r29 since it might increase the temperature differences. During the time the ground wasn't shorted yet the temperature jumps within 10 degrees range positively or negatively with averaging already. Take note that 5 temperatures were averaged.

What I've noticed now after decreasing the resistance is that it still jumps by 1 degree but it goes back quickly to the right temperature which takes only few seconds unlike before it takes a minute before it goes back to the right temperature (I'm talking about 1 degree temperature jump only). I can't really say yet if this would finally work since sometimes it takes hours to see the real problem. I'm still monitoring it right now.

Thanks really.

 

[Sajjadkhan]

Then remove averaging to see how much it is jumping since averaging is not going to let you know that.

 

[romel_emperado]

What I've noticed now after decreasing the resistance is that it still jumps by 1 degree but it goes back quickly to the right temperature which takes only few seconds unlike before it takes a minute before it goes back to the right temperature (I'm talking about 1 degree temperature jump only). I can't really say yet if this would finally work since sometimes it takes hours to see the real problem. I'm still monitoring it right now.

Is the jumping of 1 degree occurs when the relay turns on? if yes then the voltage is still insufficient..

 

[Sajjadkhan]

Yes if it changes with relay on then still voltage is insufficient but if it also happens without it then its ADC internal error which all ADC do have...

 

[lloydi12345]

No, the temperature doesn't really change with the relay when turned on or off. Sometimes when the relay is already on or being turned on then the temperature changes. It does the same also sometimes when the relay is already off or being turned off. It's really random.

-Still monitoring for some results-

---------- Post added at 13:39 ---------- Previous post was at 12:36 ----------

The problem still occurs. I checked it on average mode and it stays 1 degree higher from its right temperature and goes back for 3 mins. Still the same thing that happens even when the resistor wasn't changed. Well, I can't find anymore problem here. I think this would be fine since I was given anyway maximum of 3 degrees positive or negative error.

Thanks guys.

 

[Sajjadkhan]

So this is happening without the relay right? I mean that uncertain big jumps are gone? If yes than these errors are normal since you are not in an ideal situation and i have read that these thermocouples and thermistors are very sensitive so even a little air which we can not feel will change a value little bit, I am sure that you go with the modify resistor and when you will enclose the circuit then this error will be much reduced.

---------- Post added at 11:07 ---------- Previous post was at 11:07 ----------

And if you problem is solved then mark this thread as solved so it can help others.

 

[lloydi12345]

Well yeah, although the changing the resistance connected to the base didn't help the grounding issues did. Thanks anyway.