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[[File:Optoisolator.jpg|thumb|right|100px|Schematic symbol for a phototransistor optocoupler.]]The '''vactrol''', also known as '''resistive opto-isolator''' (RO), or '''photoresistive opto-isolator''' in its simplest form is an analogue optoisolator or '''optocoupler''' consisting of a [[LED]] and a [[light-dependent resistor]] (LDR) in the same package. Light output from the LED varies as the current passing through it, the light strikes the LDR, varying its resistance in turn, in effect this gives a current-controlled resistor.<ref name="ts">[[Tim Stinchcombe]],
The name is a trademark introduced by Vactec, Inc. in the 1960s, has since since largely become genericized to cover all such available devices, whoever might make them. Through acquisitions etc., Vactec became part of Perkin Elmer, and recently it appears the Vactrol trademark has passed to a company called Excelitas.<ref name="ts" /><ref name="wp" /> Like a lot of other products used in SDIY though, this is yet another device that is about to become end of life. As the photoresistors typically use CdS (Cadmium Sulphide) in their construction, Cadmium is classed as a hazardous substance under RoHS and production is due to end in 2015. Production would have ended sooner, but Vactrols where given a limited exemption whilst replacement materials were researched.
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== Manufacturers ==
* Excelitas, [https://web.archive.org/web/20120707054657/http://www.excelitas.com/Pages/Product/Analog-Optoisolators-and-Optocouplers.aspx Analog Optoisolators and Optocouplers]
* Some [[Doepfer Musikelektronik GmbH|Doepfer]] modules are known to use Macron devices, [https://web.archive.org/web/20130731213605/http://macron.com.hk/specification.htm Macron specification page]
* The Silonex 'NSL' series, [https://web.archive.org/web/20120821204302/http://www.silonex.com/audiohm/index.html Silonex Audiohm Optocouplers]
* Fairchild H11FxM, [https://web.archive.org/web/20110607053714/http://www.fairchildsemi.com/tree/optoelectronics/solid-state-relay-optocouplers/solid-state-relay/ Solid State Relay Optocoupler]
{{From Muff Wiggler wiki|Analog Optical Isolators aka Vactrols}}▼
== References ==
{{reflist}}
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* This Perkin Elmer document contains a good introduction to such devices: [http://denethor.wlu.ca/pc300/optoisolators/analogoptoisolatorintroduction.pdf Analog Optical Isolators: Vactrols]
* A more complete Perkin Elmer 'databook' contains not only the spec sheets of the various types of Vactrols, but also has many useful 'application note'-type circuits of how they might be used: [http://www.datasheetcatalog.org/datasheet/perkinelmer/VT500.pdf Photoconductive Cells and Analog Optoisolators (Vactrols)]
* Current spec sheets are to be found on the Vactrol product page at Excelitas: [https://web.archive.org/web/20120707054657/http://www.excelitas.com/Pages/Product/Analog-Optoisolators-and-Optocouplers.aspx Analog Optoisolators and Optocouplers]
[[Category:Semiconductor devices]]
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