# How to build a millivolt signal conditioning circuit with compensation?

#### anoopak

Nov 25, 2023
2
I want to build a miniature circuit which perform the following:
• Measure a voltage signal between 0-20 millivolt DC signal
• Measure a voltage signal between 0-24 V DC signal
• Calculating a compensation factor as K = a Constant/voltage measured at step2
• Multiply the compensation factor K with millivolt signal of step1
• Transmit value got in step4 as standard 4-20Ma[500 Ohm] /RS485 signals
I want the circuit to be made on a single board with ICs [as tiny as possible].

Thank you.

#### Delta Prime

Jul 29, 2020
1,795
I have used this SN65hvd57 RS 485 driver/ receiver,with a high degree of success. But I prefer the Max12900

#### Attachments

• sn65hvd37.pdf
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• max12900.pdf
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#### Bluejets

Oct 5, 2014
6,853
Sounds like homework.

Moderator
Nov 17, 2011
13,633

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,633
Show us what you have done so far and where you are stuck.

#### anoopak

Nov 25, 2023
2
Show us what you have done so far and where you are stuck.
I will describe the problem in detail:
There is a calorimeter sensor which outputs a dc voltage in the range 0-20millivolt. This signal is generated from a Whetstone bridge working on an excitation current of 100milli Amperes, which is kept constant [Excitation voltage ~20V]. The sensor output is bound to change with ambient temperature [results in a change in excitation voltage also]. This excitation voltage is measured and a correction factor is derived from this excitation voltage as K. Then the corrected sensor output= indicated output X K.Presently, i am using Redlion process indicator to transmit both sensor output and Excitation voltage as Standard signal [4-20mA]to a PLC and correction is carried out in PLC.
To make this signal conditioning process simple and economic, I want to build a Custom signal conditioning board for the calorimetric sensor which can be mounted over the sensor.This board shall sense both millivolt signal from bridge and the excitation voltage and do the NECESSARY correction on sensor output and send this information as Standard signal [4-20mA or RS485] to the PLC. The resolution shall be 0.01millivolt.
For this purpose I searched for OP aMP, ADC, Microprocessor and RS485 converter chips.Being a Chemical Engineer [With limited Knowledge of electronics], I am not able to converge to specific models for the above ICs. So I want help to Choose the ICs and if possible the circuit to connect the ICs.
[ I know how to use a Multimeter, built a bluetooth car and weighing scale based on Arduino and done a lot of unsuccessful efforts to build a superstable FM transmitter. This project is too challenging for me. So request for suggestions/Tips]

#### Delta Prime

Jul 29, 2020
1,795
Does not sound like homework to me and did not sound like homework to me.
My post was deleted by the powers that be....

Just because two people agree does not make it right!
Two people are wrong!
Never one apology!
I would use a 16-bit A/D converter you need higher resolution your transmitting in the noise floor it will pull you above the noise given the parameters you have stated.
also...research "boltzmann constant"
Absolute Temperature .
Being an " Chemical engineer" you should know this...
I have also posted a recommendation for chip selection by a company known as Microchips for RS 485.

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#### Delta Prime

Jul 29, 2020
1,795
[ I know how to use a Multimeter, built a bluetooth car and weighing scale based on Arduino and done a lot of unsuccessful efforts to build a superstable FM transmitter. This project is too challenging for me. So request for suggestions/Tips
I really don't know if that's just a statement or you wish help on this subject as well. But in any case I make it a point to stay away from arduino they say it's a teaching tool but it's not. if you want to make something you just copy it.
And you will use it.

#### Attachments

• MT-002.pdf
152.4 KB · Views: 5

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,633
Sounds like homework.
At a second glance it is not. I moved the thread back to general electronics discussions.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,633
I have used this SN65hvd57 RS 485 driver/ receiver,
Undeleted, as I don't think this is homework anymore.
However, the RS485 part seems to be the smalles issue here. The basic problem is measuring the small differential voltage, applying the correction factor and then transmitting the result via RS485. The latter will require some kind of protocol.

Jul 29, 2020
1,795

#### roughshawd

Jul 13, 2020
457
Conditioning is just another word for maintaining. "Conditioning a circuit" is bringing it back to life using methodical systems, when it runs out of signal. They told me my solution was unique. I stabilized a freq, and read it into a memory module. The memory then acted like a swap freq between unstable freqs. The final circuit didn't have enough power, but it might work. The solution is probably a lot easier then that!!! I like inline amps that don't use the traditional OP factors...

#### roughshawd

Jul 13, 2020
457
On the first post
...
IC is exactly that. The point is that if you can dream up the numbers, draw the block diagram, there are computers that can build it! So you might look at it like this... Create a sensor array, stabilize a set of drivers for each readout, then only display the solutions or proofs. Somebody stop me!!!?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,633
I want some of these pills, too.

#### roughshawd

Jul 13, 2020
457
Signal conditioning is often done with a vintage style OP amp circuit. You build it with RC and a transitory that loops until the proper condition is reached. That's all about the frequencys then, hence my previous ideal. But if you over condition the circuit, it will probably lose integrity

#### roughshawd

Jul 13, 2020
457
It is really easy to saturate coils, and overdrive caps in this manner. That's why you usually start from scratch... Er.
Caloric meter? You build a circuit to meter one condition and a second circuit that meters the other condition, when compare them
... I think you need to learn about the ideal circuits, and what electronic devices really are.

#### kellys_eye

Jun 25, 2010
6,470
I think you need to learn about the ideal circuits, and what electronic devices really are.
I'm not so sure you're qualified to offer that suggestion either.

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