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Metal film vs metal oxide resistor?

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grizedale

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Hello,

which has the least inductance?...

-a metal film resistor
-a metal oxide resistor

-also, which has the better pulse withstanding capability?
 

Inductance do not depends on a type. It depends on the process how the resistance is created. If it is spiral (helix) then inductance is higher than it is cuted as meander.
Pulse robustness depends on maximal voltage of the resitors. On the other hand I have better experience with metal resistors. Use more of them in series os some high voltage variant.

Pool
 
The inductance depends more on geometry than material. For example you
now can find capacitors in both 1206 and 0612 forms, wider and shorter is
your friend, and smaller is better than bigger (until you have to get the
heat out).

Beware thin-film resistor DC and pulsed power limits, they are less robust
than thick film or bulk resistors.
 
Metal film resistors are trimmed to value by having a spiral track cut through the resistive film - they can be extremely inductive!
For best pulse performance - overvoltage for a short period/low inductance, carbon film +- 20% types are best - no spiral track to flash across. We used them to limit the current if a klystron flashed over - 26KV @ 8A supply, the resistors had anti corona caps though in normal operation the current through them was < 1mA and were about 25 cms long.
Frank
 
None of the types mentioned are non-inductive .You actually need to have a wire-wound with the bi-filar windings cross-linked to neutralize the inductive value with the reverse instantaneous currents .
Best way to do so to wind a manganin wire from cap1 to cap2 clockwise.Similarly exactly so from cap1 to cap2 ,wind a second layer in counterclockwise fashion.Take care that the lengths are exact.
 
vimalkhanna said:
None of the types mentioned are non-inductive .You actually need to have a wire-wound with the bi-filar windings cross-linked to neutralize the inductive value with the reverse instantaneous currents .
Best way to do so to wind a manganin wire from cap1 to cap2 clockwise.Similarly exactly so from cap1 to cap2 ,wind a second layer in counterclockwise fashion.Take care that the lengths are exact.
Click to expand...
Yes this is true, but the downside to non inductive wirewound geometries is they often have poor pulse withstanding capabilities, due to the fact that the start and finish of the winding are right next to each other, and flashover will often occur there.

It's pretty hard to generalize resistor types for these specifications. In fact when I need a low inductance, high voltage resistor, I'll usually just chain a bunch of old carbon comp resistors in series, rather than getting some specialized film resistor.
 

The only time I have seen a Ayrton-Perry_ resistor was as a RF load for a 50 kW MW transmitter. It hung in the roof space of the testing bay. Now one would use a water cooled resistor load, but the AP resistor did not need any water hoses or interlocks.
Frank
 
Metal film and metal oxide resistors use identical methods for patterning and trimming, so I doubt the inductance would be different. Metal oxide resistors likely have superior current pulse handling. Voltage pulse handling is a trickier issue.
 

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