Optical Isolation of an Analog Signal

[sammy-e]

il+300+analog+isolator

I am attempting to optically isolate a low voltage (0-7V) DC analog signal from a data acquisition unit. Does anyone have any suggestions ? I have been digging for an IC, but so far everything seems to be for logic signal levels. Thanks.

 

[Borber]

optical isolator analog ti

Use A/D converter and then optocoupler.

 

[CapBlack]

7b41 analog signal optical isolator circuit

Hi , I used one time IL 300-G , analog optocupler check it out .

 

[A.Anand Srinivasan]

analog signal optical isolation circuit

i believe photodiode can be used for analog cases with a properly modulated light source like LED....

 

[FvM]

iso124 aplication

Hello,

I think all suggested solutions could be meaningful. It strongly depends on the specification. To name some important parameters:

Isolation voltage
Isolation capacity
Voltage transient immunity
Bandwith
Linearity
Noise respectively resolution
Power consumption
Size and formfactor

Typically you get a tradeoff between several of these parameters

Considering todays technologies, mainly digital solutions are spreading, particularly when digital data acquisition is involved. In such cases, the system design could be orientated to isolation. As a reference for state of the art with analog solutions, I suggest to browse the topic isolation amplifiers e. g. at Analog Devices or Texas Instruments.

Regards,
Frank

 

[sammy-e]

+10v optical isolation

If it helps, the setup is a pressure transducer and the circuit is checking if the output voltage goes above a certain threshold. The voltage will be between 1 & ~7 V and any changes are generally very slow since the pressure usually goes up and down fairly gradually.

To help monitor state as a backup, there is a daq measuring the input lines and reporting back to a pc. The problem is that when the daq takes it's measurement, there is some capacitive buildup in it's measurement lines that is injecting error into the circuit.

So the idea is to optically isolate the measurement from the signal line to prevent error injection.

There aren't a lot of power, responsitivity, or form factor requirements. My main concerns are reliability and simplicity.

CapBlack: thanks, I'll be taking a look into the chip you suggested.

Borber: could you provide a link to an example of what you're suggesting? sounds like a good idea.

Frank: I hope I provided some insight as to what you were looking for...

Thanks for all the suggestions, I'll continue monitoring this thread as much as possible (min is 1/day, but prob more).

 

[FvM]

il300 unit gain

Hello,

if I understand right, optically isolation actually won't be required, only decoupling respectively buffering of the signal, may be with a OP voltage follower.

If isolations is required anyway, the suggested analog optocoupler IL300 would be probably an appropriate opion, or a Analog Device or TI analog isolation amplifiers.

Regards,
Frank

 

[sparso]

analog optical isolator ic

Check out:

www.clare.com

LOC110 or LIA100 data sheet will help

 

[sammy-e]

analog optocoupler follower

I like the idea of using the IL300, or LOC110 since I believe it is the same, but I after reading through the datasheet I am still unsure how it should be wired up.

Pg 9 walks through calculating the resistors, but I am not quite following everything...

R3 = Vb/Ipl
What is Vb and why did they pick 3V? How was 100 uA in fig 4 chosen?

What is Ifq and how do I know what it is?

R1=R2(Vm/Va - 1)
I am assuming Vm is the input voltage, but what is Va?

Does the bin selection have to do with gain? So if I want a unity gain, I would select an R5 of 30kOhm?

In calc'g R4, Vopamp is just half of whatever my Vcc is, correct?

Any insight would be much appreciated. Thanks.

 

[Siniša]

analog optical isolation

You did not read data sheet carefully. It is obvious that you don't have enough experience to implement such circuit yourself without significant ammount of effort. For single unit application as you require it, I would recommend you more integrated solution ,e.g. TI's ISO122/ISO124 or simmilar. No hasle with calculating. Vin=Vout period. You will need isolated power supply for both input and output circuits, which you will need anyway.

It is little more expensive solution in parts but it will save you a lot of time.

There are a lot of already made and packaged solutions "signal conditioners" available everywhere, already with power supply and all protection and conditioning circuits built in. They will tipically work with signals 0-10V . For example, Analog's 7B41 module (7B41-01-2).

 

[sammy-e]

Sinisa:
I've been considering the ISO124, I'll look a little more towards it or the 7B41. I'd have to agree with you on my experience level, but if someone has a hint or two IL300's support circuitry I'd really appreciate it for future reference in understanding how some datasheets work. Thanks.

 

[master_picengineer]

Hi use a Level Shifter and an optocoupler.

 

[dfullmer]

You May find this useful.

Hope it helps

dfullmer

 

[Siniša]

If you still want to use IL300, you should get some basic knowledge on opamps. there is nice reading material floating on EDAboard for that. Once you have good understanding of opamps, you could read app50.pdf available from Vishay as support for IL300. Idea behind this kind of adapters is having one of photo receivers in feedback loop and having that second photo receiver is match to first one on the same chip, so it should have same output as well. It is important to have in mind how does opto coupler work and what are it's specs.
Spending time with this data sheet and mentioned application note should give you enough insight how to design your conditioner.

Have in mind that you should have some passive signal conditioning before as well protection for input and output. Unless you would make this in large quantities it is unlikely you could save any money.

 

[kender]

Check out:

www.clare.com

LOC110 or LIA100 data sheet will help

I used LOC110 for analog galvanic isolation too. With success.

 

[m_anjom]

hi dear ALL, my offer is YOUTAB solution, in this way you have two digital opto-coupler in linear region and optical feed back , einjoy it.

fast
high band
simple
low cost


with respect