[archiver]

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:



Steve,
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.
Kevin,
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.
Al