CARBON RESISTOR (High Stability carbon Resistor). 2

[FYS]

Dear ALL,

Please can you tell me which one of the Resistor are more stable (to be used as a shunt), Carbon Film Fixed Resistor or Carbon Composition Resistor for measuring the potential across the resistor, in order to calculate the current passing through (for sacrificial anode cathodic Protection System application). The current would be in the range of 0.1milliamps to maximum of 100milliamps. The resistor would be in Operation continously over years. The operating Temperature would be -45deg.C to +45 deg.C.

Your help and early reply would be very much appreciated.

Kind Regards

 

[ScottyUK]

Composition resistors are an old technology and had poor stability and poor tolerance by modern standards. I am curious why you are not considering either metal fim, metal oxide, or wirewound types. All would be a better alternative in a DC circuit than a carbon film or composition type - selection would depend on power rating and ohmic value.

BTW, there is a component forum which might be a better place for future questions like this.


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If we learn from our mistakes I'm getting a great education!

 

[FYS]

Thanks for your reply,
I do not know about the metal film, metal oxide, and also does not to be very accurate.

where can contact / I find the BTW (I not Familiar with the term)?

BTW, there is a component forum which might be a better place for future questions like this.

 

[itsmoked]

BTW = By The Way (or also) (or you should know)

Go here and search for composite resistors.

http://www.digikey.com

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricuwe]

High pulse load capability might have been a reason to use carbon composite resistors in the past. But today you will also find pulse rated resistors using more stable technologies on the market.

 

[itsmoked]

Carbon comp resistors had zero inductance. Carbon film and metal film have oodles of inductance.

A lot of designs went haywire when purchasers couldn't find comps and switched in carbon/metal films instead.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Yeah, but this is a cathodic protection system - DC only. The thick film planar reistors are good for low inductance applications but they aren't as mechanically robust.


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If we learn from our mistakes I'm getting a great education!

 

[busbar]

FYS, have you considered using a 4-lead “Kelvin” type resistor like those at:

http://www.isotekcorp.com/productDisplay.asp?CatID=1&SubCatID=2?

They are specifically suited for current measurement where two terminals are connected in series in the circuit of interest, and two other leads are connected to the measurement circuit; for a millivolt measurement proportional to current. They also have excellent temperature coefficients.