could any engineers help me out please?

Posted by Stephen Riley at 03/27/2001 9:05 AM EST

Engineer on team #419, RAMBOTS, from Wentworth Institute of Technology and sponsors? what are they?.

Hello, this post is off of the FIRST track but i was wanting and needing a little help. I am a college student at Wentworth and I am needing a little help in finding information on solid-staet relays, opto-couplers, and opto-isolators. Are they all the same thing but diferent names for it? what exactly do they do? or if you could direct me to any website or any database that i could find this information it would be greatly appreciated, this is for a design project that I have been given and my professor is not being all to helpful. Once again I thank you for your time and effort in reading this and for any help you may give.

Stephen Riley
Wentworth Institute of Technology

Posted by Kevin Sevcik at 03/27/2001 11:59 AM EST

Other on team #57, Leopards, from BT Washington and the High School for Engineering Professions and Exxon, Kellog Brown & Root, Powell Electrical.

In Reply to: could any engineers help me out please?
Posted by Stephen Riley on 03/27/2001 9:05 AM EST:

Here’s what 5 minutes of searching on Google got me. Not a lot, but probably about as much as you need. A little more searching convinced me that SSRs, opto-couplers, and opto-isolators are all the same thing.

Posted by Thomas A. Frank at 03/27/2001 1:39 PM EST

Engineer on team #121, The Islanders/Rhode Warrior, from Middletown (RI) High School and Naval Undersea Warfare Center.

In Reply to: No Engineer, but…
Posted by Kevin Sevcik on 03/27/2001 11:59 AM EST:


Opto-couplers and opto-isolators are not necesarily the same thing, and SSR’s can be different still.

Today, where I work, the usual useage of the term optoisolator is a four terminal device where the “input” side is an optical source (an LED), and the “output” side is a transistor whose “base” control is the light generated by the input light source. These are a digital device, on or off…so the base is either putting the output transistor into cutoff or saturation.

An opto-coupler, on the other hand, could be the same as above, or it might be an analog device with a similar method of operation, and properties…in other words, the output side might be gain controlled by the amount of input signal. Such devices are great for having low power electronics like a computer control the power output of high power amplifiers.

Note that I say “today”, because in times past, such devies were made using a light bulb on the input side and a cadmium sulfide photocell (variable resistor) on the output side. But I haven’t seen those commercially in quite a few years. You could make your own, however. Just not for FIRST use (yet!).

SSR’s may or may not be optically based, depending on how they are implemented. I’ve seen ones that were optically isolated, and ones that were not.

Get yourself catalogs from Newark Electronics, Allied Electronics, and Digi-Key, and look at the selection. Then go to the manufacturers web sites for more deatils.

Tom Frank

Posted by Stephen Riley at 03/27/2001 11:35 PM EST

Engineer on team #419, RAMBOTS, from Wentworth Institute of Technology and sponsors? what are they?.

In Reply to: I am an engineer…
Posted by Thomas A. Frank on 03/27/2001 1:39 PM EST:

Thank you both for the information, it has already been put to good use, but tom i have a question for you : Do you know of any good company or model of SSR or any of the above that i asked about that would be good to regulate the temp for a soldering iron tip to about 300 C ? thanks once again.


Posted by Al Skierkiewicz at 03/28/2001 7:39 AM EST

Engineer on team #111, Wildstang, from Wheeling High & Rolling Meadows High and Motorola.

In Reply to: Re: I am an engineer…
Posted by Stephen Riley on 03/27/2001 11:35 PM EST:

There are many companies that already make great temp controlled irons. If you are trying to control temp with an opto device, there are far too many variables to deal with for that. Check out the newark, allied and digikey webs for irons and you will see what I mean. Weller (Cooper Ind) makes some great stuff and I have been using their irons for 30+ years now.
I tried to post the following reply yesterday but our provider was down. Hope this helps.
See you in Florida, stop by the pits and say hi.
There are significant differences between the components you describe even though they all have similar constructions. i.e. solid state relays can have an opto isolated control input. Solid state relays are a way of producing a “closing contact” using transistors, triacs, SCRs or FETs. The control line can be anything from 5volts up to line voltage and can be isolated such that the control circuit is never tied (connected) to the relay load circuit.
An opto isolator is intended to isolate two circuits electrically, but still allow control signals to pass from one circuit to another. The name implies a digital type of signal, on/off or PWM. The voltage regulator feedback loop in a switching power supply is a good example of this since many designs use PWM to regulate output voltage.
Opto couplers are a family of optical devices that may include switching outputs, analog outputs or variable resistance outputs. Many analog/digital hybrid equipment designers will use these devices to couple signals from outside the box, without causing noise currents to flow between different equipment. Many pro audio manufacturers will couplers to isolate remote control signals from the audio path. In my mind opto couplers are used where transformers had once been the only choice but at a much reduced cost. Couplers and isolators are terms that are used interchangeably by many people, manufacturers included.
The internet is a good place to start looking for data, and most companies that manufacture relays also make solid state relays. Crydom has a wide line as does Claire, and others. Motorola is a good source for opto devices as well as Texas Instruments.
The devices are classed as to what they are designed to do. Relays are speced by control voltage, switching voltage and current and whether AC or DC loads. (You may find reference to “zero crossing” which indicates that the relay senses when the AC waveform is crossing the 0 voltage point and only switches then.) Opto isolators are speced by voltage/current in and out and how much isolation is provided. (i.e. a 300v isolation guarantees that 300v will not arc across inside the device.) Opto couplers are speced the same and have frequency response limits as well.
Hope this helps.

Posted by Stephen Riley at 03/28/2001 2:22 PM EST

Engineer on team #419, RAMBOTS, from Wentworth Institute of Technology and sponsors? what are they?.

In Reply to: Re: I am an engineer…
Posted by Al Skierkiewicz on 03/28/2001 7:39 AM EST:

yes this does help me out, thanks Al. its making my design a lot easier especialy when i have to get this done by the 4th, otherwise i won’t be excused out of his class for nationals. thanks again everybody for all your help.

Stephen Riley

Posted by Anton Abaya at 03/30/2001 4:07 AM EST

Coach on team #419, Rambots, from UMass Boston / BC High and If only we had free donuts…

In Reply to: Re: I am an engineer…
Posted by Stephen Riley on 03/28/2001 2:22 PM EST:

opto what?

dude, u shoulda asked these engineers to just do ur hw. woulda been like 5 minutes of their time :-).

heh. dont u wish we had some real engineers on our team now?