elmquist@nachos.SSESCO.com (Chris Elmquist) (09/25/90)
Does anyone have a nifty circuit that will replicate a 0v to 5v DC signal across an opto-isolated path..?? I need to read a meter in a hostile environment with an A/D in a PC. I don't want the PC to get near this meter... this meter will be read, maybe, 10 or 15 times a second so frequency response is not critical... I've thought about serial A/D and D/A chips... but I haven't found any that use the same data format over the serial link... maybe I missed something. I've also though about a voltage->frequency ... frequency->voltage converter and this seems workable... maybe someone has a circuit like this. Any ideas would be appreciated. Thanks-- Chris elmquist@nachos.ssesco.com
larry@kitty.UUCP (Larry Lippman) (09/25/90)
In article <222@nachos.SSESCO.com>, elmquist@nachos.SSESCO.com (Chris Elmquist) writes: > Does anyone have a nifty circuit that will replicate a 0v to 5v DC > signal across an opto-isolated path..?? I need to read a meter > in a hostile environment with an A/D in a PC. I don't want the > PC to get near this meter... this meter will be read, maybe, 10 or > 15 times a second so frequency response is not critical... > ... > Any ideas would be appreciated. Use an "isolation amplifier" specifically designed for this purpose, such as one manufactured by Analog Devices, Burr-Brown, etc. You can probably obtain an encapsulated device providing 1,000 volt isolation for as little as $ 25.00 in small quanitites. My advice is to not even think of designing your own analog isolation circuit for a one-of-a-kind application. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 {utzoo, uunet}!/ \aerion!larry
grayt@spock (Tom Gray) (09/25/90)
Newsgroups: sci.electronics Subject: Re: Need analog opto-isolator or equiv. Summary: Expires: References: <222@nachos.SSESCO.com> Sender: Reply-To: grayt@halligan (Tom Gray) Followup-To: Distribution: Organization: Mitel. Kanata (Ontario). Canada. Keywords: In article <222@nachos.SSESCO.com> elmquist@nachos.SSESCO.com (Chris Elmquist) writes: >Does anyone have a nifty circuit that will replicate a 0v to 5v DC >signal across an opto-isolated path..?? I need to read a meter >in a hostile environment with an A/D in a PC. I don't want the >PC to get near this meter... this meter will be read, maybe, 10 or >15 times a second so frequency response is not critical... > >I've thought about serial A/D and D/A chips... but I haven't >found any that use the same data format over the serial link... >maybe I missed something. > >I've also though about a voltage->frequency ... frequency->voltage >converter and this seems workable... maybe someone has a circuit >like this. > >Any ideas would be appreciated. > >Thanks-- Chris >elmquist@nachos.ssesco.com The most straight forward way to do this would would be to linearize an opto-coupler. You can do this by using two opto-couplers. One opto-coupler is used to create a feedback loop around an op amp. The op amp is used to create a constant current source in the feedback path - a typical cook book op amp circuit. The input porion of the opto-coupler is driven by a current which you wish to repilcate across some isolating barrier. It is connected to the current sourc source and to ground. The ungounded input of the opto is connected to the inverting input of an op amp. The output of the op amp is connectd to ground through the output section of the opto-coupler. A feedback lop is set up with the optical connection of the opto-coupler and the circuit is stable. Now the interesting part occurs. Connect the light emiiting portion of another opto in series with the output of the op amp and the light emiitoing portion of the first opto. The feedback of the op amp is making sure that the current though the light emitting prtion of the first opto is usfficent to produce the input current in its light receiving portion. Similarly the same current is flowing through the light emitting portion of the second opto as that of the first. Thus the current in the light receiving prtion of the second opto will be the same as the current in the light receivng portion of the first opto. However this is the input current which is supposed to be transferred across the barrier. The op amp feed back calculates the voltages required to create a liner current transfer mechanism from two opto's. As long as the transfer characteristics of the two opto's are amtched, there will be a linear tranfer characteristic across the barrier.
henry@zoo.toronto.edu (Henry Spencer) (09/25/90)
In article <222@nachos.SSESCO.com> elmquist@nachos.SSESCO.com (Chris Elmquist) writes: >Does anyone have a nifty circuit that will replicate a 0v to 5v DC >signal across an opto-isolated path..?? ... >I've thought about serial A/D and D/A chips... but I haven't >found any that use the same data format over the serial link... Of course, if you're willing to throw in a few more optoisolators, you can just use parallel-i/o converters, which generally agree on the data format. :-) -- TCP/IP: handling tomorrow's loads today| Henry Spencer at U of Toronto Zoology OSI: handling yesterday's loads someday| henry@zoo.toronto.edu utzoo!henry
paulh@cimage.com (Paul Haas/10000) (09/27/90)
In article <4054@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: ]In article <222@nachos.SSESCO.com>, elmquist@nachos.SSESCO.com (Chris Elmquist) writes: ]> Does anyone have a nifty circuit that will replicate a 0v to 5v DC ]> signal across an opto-isolated path..?? I need to read a meter ]> in a hostile environment with an A/D in a PC. I don't want the ]> PC to get near this meter... this meter will be read, maybe, 10 or ]> 15 times a second so frequency response is not critical... ]> ... ]> Any ideas would be appreciated. ] ] Use an "isolation amplifier" specifically designed for this ]purpose, such as one manufactured by Analog Devices, Burr-Brown, etc. ]You can probably obtain an encapsulated device providing 1,000 volt ]isolation for as little as $ 25.00 in small quanitites. ] ] My advice is to not even think of designing your own analog ]isolation circuit for a one-of-a-kind application. ] You can also put a voltage controlled oscillator in the hazardous area and use it to drive an opto-isolater. Or choose your favorite way to convert an analog signal to a digital one. --- Paul Haas paulh@cimage.com (313) 677-2412
rick@sesi.UUCP (Rick Lotoczky) (09/28/90)
> In article <222@nachos.SSESCO.com> elmquist@nachos.SSESCO.com (Chris Elmquist) writes: > >Does anyone have a nifty circuit that will replicate a 0v to 5v DC > >signal across an opto-isolated path..?? ... > >I've thought about serial A/D and D/A chips... but I haven't > >found any that use the same data format over the serial link... > Another way to do it would be to send a pulse width modulated signal through an opto-isolator to a low pass filter on the other end. The LPF will convert the PWM to an eqivalent analog signal. You will most likely have to linearize this circuit, but that can be easily done in software. I don't know what kind of accuracy you need, but 0.5% or so should be attainable. rick -- Structured Electronic Systems, Inc. | ...uunet!mailrus!sharkey!cfctech 650 Red Oak Lane | !rphroy!trilby!sesi!rick Rochester, MI 48063 | (313) 652 4809 |