[nkd]

Has anyone used these before? 0.1% tolerance rating...
I was considering using them for an ultimate stepped attenuator, but not sure if I might find something better. Obviously I want to be sure before i spend £150 on resistors!

 

[PinkFloyd]

Quote:

Originally Posted by nkd Has anyone used these before? 0.1% tolerance rating... I was considering using them for an ultimate stepped attenuator, but not sure if I might find something better. Obviously I want to be sure before i spend £150 on resistors!

The 0.1 % part means jack ****. What you want for a stepped attenuator are resistors with a low temperature coefficient. The RC55Y have a temperature coefficiency of 15ppm/C which is pretty low compare with standard 1% metal film resistors which generally have a temp coefficiency of 50 parts per million 50ppm/c

So, to answer your question, the RC55Y is "ideal" for use on a stepped attenuator.

If you can find any standard metal film resistors with a temp coefficiency of 15ppm/C then use them instead of the RC55Y's ..... tolerance doesn't matter as you can hand match 1% resistors. I doubt you'll manage to find any standard metal film resistors with a low temp coefficiency but, if you do, then let us know!! You'll find that most of them are around the 50ppm/C region but I've heard people say that 1% resistors (cheap) with a 15ppm/C still exist but they're hard to find.



All the best.

Pinkie.

 

[guzzler]

Rapid Electronics sells TruOhm .4W resistors in a 1/4 W package. 0.1% tolerance and ±15ppm temperature coefficient. They sell in quantites of 1, priced at 25p a piece. I've been using them for ages and thing they're just great.

Order codes 63-1000 to 63-1756 in the current Rapid catalogue

g

 

[Daroid]

Just a small, short, general question - what does the temperature coefficient indicate ? Why is "less better" ? - i.e. the RN55 Vishay Dale resistors are 150 PPM/deg. cent., and BC PR01 1W @70 degrees centigrade are 250 PPM/deg. cent.
Something tells me that resistors with a higher temperature coefficient would change it's value/resistance significantly more as the temperature rises, in comparison to a e.g. 15 ppm/c resistor ?

 

[guzzler]

you're pretty much right, the temperature coeffecient is a measure of how much the resistance changes from the value quoted at a certain temperature (I think that it's 70°C, as that's where the power rating is taken, but I'm quite possibly wrong on that). Say you take a 1M resistor that's rated ±15ppm/°C, for every 1°C change, you'd expect the worst case resistance change to be 15Ω.

Different materials have different temp. coeffecients, with carbon film being the least stable, and metal film typically offering the best temp. stability.

g

 

[PinkFloyd]

Quote:

Originally Posted by guzzler Rapid Electronics sells TruOhm .4W resistors in a 1/4 W package. 0.1% tolerance and ±15ppm temperature coefficient. They sell in quantites of 1, priced at 25p a piece. I've been using them for ages and thing they're just great. Order codes 63-1000 to 63-1756 in the current Rapid catalogue g

Nice one Guzzler I'll order some of those from rapid they seem very reasonabler @ 25p each

Mike.