TEMPERATURE STANDARD FOR IR EVALUATION

[falco]

Hi! When performing infrared Testing of electrical panels, I have found that some components such as relay or timers have a temperature rise over a 40ºC of 20ºC and sometimes 30ºC even 54ºC. As I have been informed electric and electronic components are dseigned to perfectly operate if the temperature rise remains below 65ºC over a temperature of 40ºC.Is this correct? CAn anyone tell me if we should take the temperatur of 40ºC as the reference temperature or we should select the ambient temperature or which is the right tempertur to choose to have a good evaluation? Are ther e any standard that I must Know that may help me?
Thanks for your help
REgards

 

[IRstuff]

That depends on your requirements.

Most of the time, component outer case temperature should be kept below 65°C, to preventing burns to maintenance personnel or nosy engineers ;-).

Your reliability requirements would dictate how hot you can allow the components to get.



TTFN

 

[Warpspeed]

This is a complex topic, it really depends upon the application.

In my experience some components work fine at high surface temperatures for which they are designed, but as IRstuff says, there are also safety considerations.

There is also the problem of hot components cooking other nearby less heat tolerant components.

For instance normal commercial ceramic/vitreous wirewound resistors are commonly rated for 250C surface temperature RISE above ambient at full rated power. This will easily toast anything else in the vicinity. So while the resistor itself might be quite happy, other nearby components may not be.

My own personal (rule of thumb, he he) method is that I should be able to leave my thumb on a component for a full minute without great discomfort. This might equate to about 55C in practice.

So for example a 25 watt wirewound resistor with 250C rated rise, might run continuously at 3 watts, with a 30C rise and a 60C surface temperature in still 30C air.

 

[CarlRhino]

I use a very similar rule as WarpSpeed although i did do a project with a triac and two resistors that got pretty hot... to hot to leave your finger on at all... i had a phew running for over a year... The only issue is that over time the solder will dry up though i was suprised at how well the circuit lasted at such high tempratures...

In answer to your question you will really have to look at the data sheets for all the diffrent components and work out what effect the temprature will have on the circuit...