4 ms·
In a product design class, the prof asked us to draw the distribution of resistors in a bag of, say, 5-ohm resistors, bought from a local electronics shop. It
by dmlorenzetti 14y ago
In a product design class, the prof asked us to draw the distribution of resistors in a bag of, say, 5-ohm resistors, bought from a local electronics shop.
It turned out that a normal distribution centered at 5 ohms was not quite right. It was a normal distribution, but with a deep notch taken out right at 5 ohms. All the resistors that tested to very close tolerance had been bagged separately, and sold at a higher price.
(The context was why you might want to put, say, four 5-ohn resistors in series, rather than just use one nominal 20-ohm resistor.)
- juiceandjuice 14y agoI hope your product design class covered error propagation, because one 1% 20 ohm resistor would still be cheaper and more precise than 4 5% 5 ohm resistors.
- JshWright 14y agoI think his point was that it would be better assuming you used the same "grade" resistor.
- klodolph 14y agoBut four 5%-tolerance 5-ohm resistors could be chosen to add up to almost exactly 20 ohms, but a 20-ohm resistor would never be 20 ohms due to the notch. In the old days, it might have been cheaper than the more accurate resistors. These days, high precision resistors are relatively inexpensive.
- raverbashing 14y agoApparently you can take an off the shelf resistor and 'tune it' by sanding the exterior, so to increase it slightly. But of course it's better when the tolerance doesn't matter (or only of a few components)
- hexagonal 14y agoThat'd work for a bare piece of wire, but a resistor is covered with enamel.
- raverbashing 14y agoUnless you sand enough to go through the enamel and reach the conductive surface