Hi everyone! I hope this section of the forum is the correct one for the question I am about to ask.

I should make a circuit that amplifies an analog signal [0 ... 500uV] into [0 ... 5V]. We have lm339n in the lab, but I read that it is a comparator and cannot be used as an amplifier, so I opted for an op07.
The questions I ask are twofold:

1) what op amp should I use for this purpose?
If you know of integrated circuits or modules that perform this task let me know

2) is the circuit I made (which I simulated and it works) ok?
I think using a 100kohm resistor and a 10 ohm resistor can be a problem as they have very different values.

Thank

 

hi luca,
Welcome to AAC.
Please post your LTS asc file
E

 

hi luca,
Welcome to AAC.
Please post your LTS asc file
E

There are so many circuits in the schematic file because I did several tests at different times. Zooming out, the circuit I'm talking about is the one in the rectangle with the writing in bold "this one".

 

Hi luca,
Is this one, I have extracted and named it luca1.asc, so that other LTS helpers have a direct copy.
I have changed the input to 0v through 500uV to show any change in output.

E
Corrected my error in extracting your file.

 

Hi everyone! I hope this section of the forum is the correct one for the question I am about to ask.

I should make a circuit that amplifies an analog signal [0 ... 500uV] into [0 ... 5V]. We have lm339n in the lab, but I read that it is a comparator and cannot be used as an amplifier, so I opted for an op07.

What is the frequency of your signal?
What is the output impedance of your signal?
Is your signal single-ended or balanced? (a transducer, for which neither terminal is earth, for instance)

 

 

Your first circuits used a 54 years old 741 opamp that has way too much noise and input offset voltage for the gain of 10 thousand times.
The circuit with the three OP07 opamps has an extremely low input resistance.
The OP07 opamps have low input offset voltage but they have much more noise than a modern audio opamp.

 

What is the frequency of your signal?
What is the output impedance of your signal?
Is your signal single-ended or balanced? (a transducer, for which neither terminal is earth, for instance)

What is the frequency of your signal?
What is the output impedance of your signal?
Is your signal single-ended or balanced? (a transducer, for which neither terminal is earth, for instance)

At the input of the opamp circuit there is a signal coming from a load cell with the following characteristics:
Condition: 100% new
Item type: load cell
Range: 0 ~ 5 kg, 0 ~ 10 kg, 0 ~ 20 kg, 0 ~ 30 kg, 0 ~ 50 kg, 0 ~ 100 kg (optional)
Output Sensitivity: 1.0-1.5 ± 10% mV/V
0 output: ± 2% F.S
Nonlinear: 0.3% F.S
Delay: 0.03% F.S
Repeatability: 0.03% F.S
Creep (30 minutes): 0.2% F.S
Temperature sensitivity drift: 0.1% F.S/10°C
Temperature drift 0: 0.1% F.S/10°C
Material: stainless steel
Resistance: 350Ω
Insulation Resistance: ≥5000MΩ/100V DC
Use voltage: 0-10 V
Operating temperature range: -20 ~ 80 ° C
Safe overload: 150%
Extreme overload: 200%
Cable connection: Ex+: red;Ex: black;Sig+: green;Sig-: white

The amplifier circuit should bring the output signal (coming from load cell) from 0 to 5V. Also I was told that there would be a possible offset of 1 mV to remove

 

hi luca,
As you are using a Load Cell, why have you posted a single input amplifier circuit.?
It should be a differential or a INA type.
E

 

hi luca,
As you are using a Load Cell, why have you posted a single input amplifier circuit.?
It should be a differential or a INA type.
E
[/CITAZIONE]

You are absolutely right, I forgot to report that after the load cell there is a circuit that automatically brings the cell voltage to [0 to 500uV], I only have to do the final amplification part (to bring it from 0 to 5V).
Since that circuit between cell and amplifier stage is made by another guy in my school, I only reported the latter.

I'm sorry for the confusion and the lack of some data, but if I can ask the question again I ask for some advice on how to realize the complete circuit, that is a circuit that amplify the signal coming from the load cell in a [0..5]V.

(the data of the load cell I have reported in one of the answers above)

Thank you so much for the patience.

 

hi luca,
As an example, this circuit uses a INA AD623 amplifier.
You can construct INA's using regular OPA's , but will not be as good as the actual type.

You could also build a Differential Amplifier, using regular OPA's.

Which option are you considering.?
E

 

Your load cell's resistance is 350 ohms then its signal is killed by your input resistance of only 10 ohms.

 

Your load cell's resistance is 350 ohms then its signal is killed by your input resistance of only 10 ohms.

hi agu,
My circuit in post# 11 is an INA, so how can you say it has Low impedance.?

Or are you referring to post #4, the TS's original, now not being considered as suitable.???
Which was never intended to be a Bridge input amplifier, but a secondary OPA AFTER the initial INA Stage Bridge amp.

Come on 'agu' keep up.

Eric

 

hi luca,
As an example, this circuit uses a INA AD623 amplifier.
You can construct INA's using regular OPA's , but will not be as good as the actual type.

You could also build a Differential Amplifier, using regular OPA's.

Which option are you considering.?
E
View attachment 264413

Thanks!!! I'm reading the AD623 datasheet and have a couple of questions for you:

1) How did you calculate the 350 ohm resistors? What are they used for? Can I connect the load cell directly to the AD623?

2) On page 25 of the datasheet it says Rlim to be added in the two inputs to avoid overvoltage and diode breakdown ... and it is calculated as follows: Rlim = (Vover+0.7-Vs)/10mA. If I wanted to add it, is it correct to set Vover = 0.3V?

3) How much is V2 in the REF pin? I know you can set it to 0 since it references with Voutput. With V2 did you add an offset ?

Thank you very much again for the speed of response.

 

hi luca.
1) How did you calculate the 350 ohm resistors? What are they used for? Can I connect the load cell directly to the AD623?
They are the simulation model for the Load cell bridge that you are using.
Your Load Cell replaces those resistors.

2) On page 25 of the datasheet it says Rlim to be added in the two inputs to avoid overvoltage and diode breakdown ... and it is calculated as follows: Rlim = (Vover+0.7-Vs)/10mA. If I wanted to add it, is it correct to set Vover = 0.3V?
Add a 4k7 resistor in each input, between the Load Cell and AD623

3) How much is V2 in the REF pin? I know you can set it to 0 since it references with Voutput. With V2 did you add an offset ?
Are you using a single or double supply for the AD623.?

E

 

hi luca,
As an example, this circuit uses a INA AD623 amplifier.
You can construct INA's using regular OPA's , but will not be as good as the actual type.

You could also build a Differential Amplifier, using regular OPA's.

Which option are you considering.?
E
View attachment 264413

I created the circuit you made but the simulation is really slow, I attach the screenshot I made after a minute of starting the simulation. I don't know if I did something wrong in drawing the schematic or in importing the component AD623 :/

I use a single power supply.

 

hi luca.
Please post your simulation file, I will try it.
E

 

hi luca.
Please post your simulation file, I will try it.
E

Where is the simulation file? I started using LTspice recently and I am not very familiar with it.
I have .raw .op and a .txt file in the folder where I saved the project

 

hi luca,
It is the .asc file
E

 

hi luca,
It is the .asc file
E