Dc voltage measurement with isolation

danadak

Joined Mar 10, 2018
3,578
Battery operated micro, like ATTINY85, feeding a fiber optic link with a freq
or pulse width, decode on other side.

Same approach only measure DC, convert to a frequency (V/F converter),
send thru transformer, convert back on other side.

Wireless with ESP8266 or ESP32. Do it with LAN or Bluetooth or Radio.

What accuracy, resolution do you need ?


Regards, Dana.
 

Analog Ground

Joined Apr 24, 2019
156
For high accuracy, Analog Devices (analog.com) makes isolated DC/DC converters and isolated analog-to-digital converters (ADC) which work together for this sort of thing. For example, the ADuM6000 is an isolated DC/DC converter and they have several isolated ADCs. There are also isolated amplifiers which work with the DC/DC converter and you can use an ADC on the micro-processor side. Finally, it is possible to use opto-couplers for a lower cost and lower accuracy solution.

What accuracy do you need?
 

Analog Ground

Joined Apr 24, 2019
156

MrAl

Joined Jun 17, 2014
6,513
Yes linear opto or microcontroller ADC feeding a standard opto then a microcontroller receiver and display or DAC output.
 

danadak

Joined Mar 10, 2018
3,578
I want to ensure isolation between circuit and microprocessor. I think optocoupler is reasonable solution.
Pay attention to the G variation of the analog coupler approach, its quite poor.
Better off converting measurement to digital, then using a digital coupler and
downstream end just converting digital numeric back to analog reading.

What accuracy are you trying to achieve ?

V/F >> F/V (micro measuring frequency), or same for pulse width....


Regards, Dana.
 
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Thread Starter

Researcher50

Joined Jul 16, 2019
9
For example ;I use RBE-0505S DC/DC CONV 1W 5VDC 5VDC 200mA SIP7, when the input voltage of RBE-0505S is 3 VDC, is the output voltage 3VDC? Does RBE-0505S have 1:1 ratio?
 

rsjsouza

Joined Apr 21, 2014
204
As others have said, you need to decide where to partition your system - either between the signal conditioning and the ADC (requiring either an isolation amplifier or an isolating ADC), or in the digital communications channel (using simpler optocouplers and leaving the input OPAmp + ADC on the high voltage side). Keep in mind that each approach has upsides and downsides.

Your last reply seems to suggest that you are trying to use a DC-DC converter to measure the input voltage. Is that what you mean? Its datasheet says the input voltage is 5V ±10%, thus you can't apply 3V at its input.

As for part suggestions, in addition to AD's there are also some TI isolating amplifiers such as the ISO122, which goes to ±10V input range, thus scaling quite nicely to 100V. I have also used the ISO1211/1212 for the digital data transmission, but I haven't used their isolated ADCs.
 
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