Hi warm,
Looking over your 150R test and the fact you are using LM358, with a single 5V supply, I don't see how you can measure +0.0475Volts at the ADC input, there is a problem with your simulator.??

Have you tried measuring the final OPA Vout when the ADC A0 is not connected?

E

View attachment 301783

Hi ericgibbs,
Yes, i check it's showing same value
i am using proteus 8 professional software

 

Hi warm,
This is the 150R circuit using LM358, it works OK.
E

Note: as I had said before any Vout to the ADC over +1.1V will always give 1023 ADC counts, due to using the Internal Vref of 1.1v


View attachment 301785

Hi ericgibbs,
I think there is problem with my simulator i think i should make the hardware and give it a test.

 

Hi
This is the UNO project built using a 10K pot, and my Sketch, it works as expected.
E

 

Hi,
This is a copy of my test Sketch.
Note the Voff from the OPA is set to 0V, change it to the actual Voff when you use real hardware.

E

float Volts; //voltage read by arduino
float tempC; //final temperature in degree celsius after calibration
float temp1; //temperatuere before calibration
float calibration; //calibration
float Rx; //Resistance of PT100
float C = 100.0; //Constant of straight line (Y = mx + C)
float slope = 56.00; // Slope of straight line (Y = mx + C)
float R0 = 100.0; //Resistance of minimum temperature to be measured (at 0 degree)
float alpha = 0.00385; // value of alpha from datasheet

float voff =0.0; // OPA Vout Offset ***************************

int Vin = A0;
void setup() {
Serial.begin(9600);
pinMode(Vin, INPUT);
analogReference(INTERNAL); // Taking internal reference 1.1V ADC of arduino
}

//loop function
void loop() {
takeReading();
delay(1000);
}

void takeReading() {
Serial.print("analog Reading: ");
Serial.print(analogRead(Vin));

Volts = (analogRead(Vin));
//converting bits of voltage into voltage
Volts = (analogRead(Vin) / 1023.0) * 1.1;
// correct for zero offset
Volts = (Volts-voff);
// & respan 0v to 1.1v
Volts = Volts * (1.1/(1.1-voff));

Serial.print(" Volts : ");
Serial.print(Volts);

Rx = (Volts * slope) + C; //y=mx+c
Serial.print(" resistance : ");
Serial.print(Rx);

temp1 = (Rx / R0 - 1.0) / alpha; // from Rx = R0(1+alpha*X)
tempC = temp1 - calibration; // Final temperature in celsius
Serial.print(" Temp : ");
Serial.println(tempC);

}

 

Hi
This is the UNO project built using a 10K pot, and my Sketch, it works as expected.
E
View attachment 301788

hi ericgibbs,
Yes you are right there is problem in my simulator even i supply 1.2V directly in A0 pin or arduino it shows analog reading of 465.

 

Hi ericgibbs,
can you please try the static value for R2 like 100,120,150 ohm.
And see the Vadc.
Bcz i have used another simulator (tinkerCad) and the issue is same no matter what value i choose like 100,120,125 etc.
the Vadc remained same (i.e. 3.33mv).

 

Hi warm,
This is the LTSpice simulation for those values of PT, also added the maximum ie: 160R
E

 

Can someone explain me why in this circuit (Attached PDF) the OP of U2 is same for both the resistor value (i.e 100 & 150 ohm)
and also U3,U4 are voltage follower which is simply pass the input voltage ( Vin = Vout as i know ) both are powered with 5v
but they don't pass the same voltage ... whyyy?? ( Vin=0.65 and Vout=1.489 )
For U2 as differential amp it should output 4.7(1.487-1.228) as per resistor values but it is not doing as expected.
Am I doing something wrong ?
Bcz I have tried the same circuit in other software (like Tinkercad, falstad ) but results are almost same.

 

hi warm,
This is a strange problem?
Try making a sim circuit using just one OPA as an inverter, see what the sim shows
E

 

It seems that for some reason the simulator is not incrementing the variable. I don't use simulators and so that is what it looks like.
So it is a simulator problem, not a circuit operation problem

 

So it is a simulator problem, not a circuit operation problem

Bill,
If you read the last few posts, you will see that the TS has been made aware of that a number of times, we know by using the LTSpice simulator that the circuit is viable.

Also, the circuit built on my work bench, works as expected.
E

 

Bill,
If you read the last few posts, you will see that the TS has been made aware of that a number of times, we know by using the LTSpice simulator that the circuit is viable.

Also, the circuit built on my work bench, works as expected.
E

Hi ericgibbs,
Hope you are fine.
The overall circuit is working normal but there is very fluctuations on deciimal values.

 

Hi warm,
Good to hear you are making progress.
What was wrong with your simulations?

Please post a diagram of your final circuit and the Arduino Sketch, I will run it on my IDE.
E

 

Hi warm,
Good to hear you are making progress.
What was wrong with your simulations?

Please post a diagram of your final circuit and the Arduino Sketch, I will run it on my IDE.
E

Hi ericgibbs,
I made the same circuit in different software and test the different - different values ( Act as PT-100 on different Temp. )



Here for 100 Ohm the OP is 860.63 mV.

Some modification are done so it gives appx correct value for 59.57 to 150 Ohm

Online Simulator LINK

Please Open the attached file (PT_100_Final.txt ) in the Simulator.
In real circuit it gives the fluctuation in decimal values.

 

Hi warm,
In a LTSpice simulation, the results are steady. [used the first value in your post #52]
Do you have an actual circuit diagram to post and if possible a photo of your project, it appears to be very electrically noisy.
E

analog Reading: 148 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.08 Temp : -75.65
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 150 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 150 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.08 Temp : -75.65
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 150 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.08 Temp : -75.65
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15

 

Hi warm,
In a LTSpice simulation, the results are steady. [used the first value in your post #52]
Do you have an actual circuit diagram to post and if possible a photo of your project, it appears to be very electrically noisy.
E

analog Reading: 148 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.08 Temp : -75.65
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 150 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 150 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.08 Temp : -75.65
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 150 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.08 Temp : -75.65
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.47 Temp : -74.64
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 148 Volts : 0.16 resistance : 70.28 Temp : -75.15
analog Reading: 149 Volts : 0.16 resistance : 70.28 Temp : -75.15

Hi ericgibbs,
The circuit diagram is same but change resistance values to read from -100 to 150 °C (59.57 to ~160 Ohm) instead of 0 to 150 °C (0 to ~160 Ohm) .


Project photo

 

Hi warm,
This project like a school or college assignment, so I have moved the thread to the Homework forum.
Why have you changes the temperature range from 0C to 160C to -100C to 150C ?
I will check out your circuit.

The photo shows the front face, but I cannot check the wiring on the back of the board?
What are the OPA types?

E

 

Hi warm,
This is the LTS simulation of your latest circuit, -100C through +150C.

The Xaxis V(vt) is the temperature scale.

E
Added: Arduino result for ~ -100C

analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.23 Temp : -101.09
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 46 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 48 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 46 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 46 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.23 Temp : -101.09
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.23 Temp : -101.09
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84
analog Reading: 47 Volts : 0.05 resistance : 60.33 Temp : -100.84

 

Hi warm,
Checking your photo of the PCB, what is the function of the 10k potentiometer?
If it represents the PT100, it is totally unsuitable for that purpose.

To get satisfactory test result, ideally it should be a multi-turn trim pot of 500R or 1k.

Also, on the PCB, I do not see any power supply decoupling capacitors.
E

 

Hi warm,
Checking your photo of the PCB, what is the function of the 10k potentiometer?
If it represents the PT100, it is totally unsuitable for that purpose.

To get satisfactory test result, ideally it should be a multi-turn trim pot of 500R or 1k.

Also, on the PCB, I do not see any power supply decoupling capacitors.
E

Hi ericgibbs,
I Need to change temperature range from 0C to 160C to -100C to 150C as the same circuit can be used in both the freezer demo (-86 and 2-8C)
And I made this as a quick model to check how it's working, not as a final prototype.
I used 10K pot to adjust the reference voltage for differential amp BCZ I don't have exact 2.7K in my case 0.268V is working nice (some noise is present)
Apology, totally forgot to add filtering & decoupling Cap here, going to build new one. Keeping all your instructions in mind, hope it will be better.