Isolation requirement for Voltage measurement

Thread Starter

Bhavik700

Joined Jan 17, 2023
8
I am developing IoT device using ESP32.
I am using ESP32 along with ADS1115 for voltage measurement of my equipment.

My electrical device operates with following parameter : ~0-5 V DC , 25 Amp with constant current mode adjustment prior to operation.

I want to measure this voltage change across my device. I am planning to use voltage divider to sense voltage.

1.Can I use configuration as per attached picture?

2. Do I need to isolate my device+ Voltage divider and ESP32+ADS1115 circuit ? If yes then how shall I isolate it?
IMG_20230117_203044~2.jpg
 

Thread Starter

Bhavik700

Joined Jan 17, 2023
8
hi B700
Welcome to AAC.
Have you considered using the ESP32 onboard 12Bit ADC.?
E
Thank you for reply.

ESP32 onboard ADC is not accurate and stable enough for my application.

With ESP32+ADS1115 I am getting 2 decimal point accuracy.

My question is about isolation. Since my electrical device and ESP32 are fed from different voltage sources, I am wondering if i need to isolate two circuit or not.
 

ericgibbs

Joined Jan 29, 2010
18,835
hi,
So, providing all the devices share the same 0V/Common, the resistive divider will work.
What are the divider values.?
E
 

Thread Starter

Bhavik700

Joined Jan 17, 2023
8
Then why is 12-bit, 3 digit+ accuracy not accurate enough?
Thank you for your reply.
Hi I don't have problem with accuracy.

My question is , can I have common 0V line for both of my circuit? Or do I need to use isolator between 2 circuit.
 

MrSalts

Joined Apr 2, 2020
2,767
Then why is 12-bit, 3 digit+ accuracy not accurate enough?
Read about the skewed voltage vs count of the ESP32 and you may understand. Also, the device the OP selected is 16-bit. So, if he specified it, paid for it, let's just assume he wants or needs 16-bit of reasonably linear resolution.
 

ericgibbs

Joined Jan 29, 2010
18,835
My question is , can I have common 0V line for both of my circuit? Or do I need to use isolator between 2 circuit.
Hi B,
I have already answered your question in post #6.

With ESP32+ADS1115 I am getting 2 decimal point accuracy.
16Bit resolution ie: decimal 65535 for a 5V conversion is 5/65535=78uV/Bit, do you really need to resolve to this value.?
A Resolution of 78uV does not mean an Accuracy of 78uV

E
BTW: Can you say what the Device is within the Red box.?
 
Last edited:

Thread Starter

Bhavik700

Joined Jan 17, 2023
8
Hi B,
I have already answered your question in post #6.



16Bit resolution ie: decimal 65535 for a 5V conversion is 5/65535=78uV/Bit, do you really need to resolve to this value.?
A Resolution of 78uV does not mean an Accuracy of 78uV

E
BTW: Can you say what the Device is within the Red box.?
Yes , I am aware about difference between accuracy and resolution.

Device is some special kind of DC motor. I am also not fully aware about it as this is some kind of confidential device.
 

ericgibbs

Joined Jan 29, 2010
18,835
hi B,
Reason for asking about the 'Device' is it possible that the addition of your divider load, may affect the open circuit PD voltage of the device.?
For the resistive divider, it would be a good idea to change the 19K resistor in the Post #10 divider to a 18K and add a 2K, 20 turn trim pot.
I will be then possible to trim the output of the divider.
E
 
Top