View Full Version : traic question
December 16th, 2007, 04:19 PM
did a search on triac outputs since i didnt know anything about them. learned alot, ecspecially about leakage problems and potential shock hazards and such. but what i havent fount yet is what the advatage to using one is versus an isolated relay output. is there one? or is there a condition in which you MUST use one? thanks as always.
BITS N BYTES
December 16th, 2007, 04:31 PM
The TRIAC output is a solid state device that if sized correctly for the switched load has an almost unlimited ON/OFF lifetime.
The RELAY is an electromechanical device. The mechanical components of the relay eventually wear out so it has a limited lifetime.
The frequency of switching the outputs needs to be evaluated for each application and compared with the published specifications.
From this one can determine if they will last the lifetime of the machine.
December 16th, 2007, 08:21 PM
Also I have been told that the majority of the time that the triacs fail, they fail closed.... if you have it on a heater application this could be trouble... make sure that the over temp safeties are NOT in the PLC and will drop out the heater
December 17th, 2007, 08:35 AM
Another point is switching at zero-crossing. The triac will turn on and off when the sine wave passes through zero. A nice feature for resistive loads such as heaters because it reduces line noise. A relay switches any time, and can generate sparks when the contacts open or close.
December 17th, 2007, 11:13 AM
great info. thanks all