Zero Ohms Resistors

[frankmcvey]

... here.

Why might one need a zero ohms resistor? There's probably a simple answer, but I can't think of it!

[Amraduk]

For a link!

[ThePillenwerfer]

I believe they are used in place of wire links on PCBs that are populated by machine as they are the same shape as resistors.

— Joe

[Radio Wrangler]

sometimes you want to change a circuit and remove a resistor. Zero Ohm resistors save you re-laying the board.

Surface mount forces all tracks to want to be on the component side. zero Ohm resistors can do the job when you need a bridge and don't want to go multilayer.

David

[ms660]

I've never seen a zero ohms resistor

Lawrence.

[cmjones01]

As others have said, they're very common as links because they're easy to put on a PCB with the same machinery as normal resistors. They're also useful if you want to keep two parts of the circuit ('nets' in the design jargon) connected at only one point: join them with a 0R resistor and the PCB layout software will know they're separate and won't allow them to join anywhere else. That's handy for things like separate grounds or 4-wire sensing connections.

I like the way 0R resistors are available in a range of tolerances. Naturally, I prefer the 1% ones. I worry that the 5% ones might sometimes have a negative resistance and send my circuit unstable

Chris

[GMB]

They do seem quite bad on going a high resistance.

I have encountered several that measure several milliohms. That's way over the marked tolerance.

[Radio Wrangler]

It's alright, Chris, they can only go negative by 5% of zero Ohms.

1206 ones are rated at 0.25W, 0805 are rated at 0.125W and 0603 at 63mW. For good reliability it is important to remember to de-rate them appropriately.

They can also be used as inductors... abut 1nH in 0603.

David

[cmjones01]

Originally Posted by Radio Wrangler

It's alright, Chris, they can only go negative by 5% of zero Ohms.

That's a relief!

1206 ones are rated at 0.25W, 0805 are rated at 0.125W and 0603 at 63mW. For good reliability it is important to remember to de-rate them appropriately.

of course. Actually, I have been known to use them as fuses, as a very-low-cost easily replaceable weakest link in a power rail. The manufacturers probably don't recommend it, though!

Chris

[Herald1360]

Originally Posted by pwdrive

I've never seen a zero ohms resistor

I have. It was rather large (about a metre in diameter and two metres long), wirewound and had a stray inductance of about thirty henries. It lived in a bath of liquid helium.

We make around a thousand a year at work- they're MRI magnets, so I guess they're strictly zero ohms inductors, but the idea its being a wirewound zero ohm resistor with a lot of stray inductance appealed.

[ms660]

I was thinking about the MRI stuff when I did my other reply.

In yet another former life I was a site chippy for some years, had the job of constructing a room within a room for an MRI scanner at Treliske Hospital near Truro, special fixings for the wall cladding etc all non magnetic, I got to witness the techs ramping the current up, I think the scanner was made by Philips Medical?

Also gave the "plumber" a helping hand who put all the pipe work and special lagging in, the gubbins was in a separate room and looked very technical, there was a lot of it.

Lawrence.

[G6Tanuki]

Originally Posted by frankmcvey

Why might one need a zero ohms resistor? There's probably a simple answer, but I can't think of it!

They're often used as jumpers for program-selection in radio equipment.

Manufacturer ships all the radios with the same software, but the national/regional customisation [for things like display-language, frequency-coverage and channel-step-size] is selected by adding/removing zero-ohm jumpers to the circuit-boards - which working with pull-up resistors then invoke the appropriate software functionality when the radio's powered up.

Adding/removing these jumpers to change the tuning range of commercial radios is a standard bit of amateur radio these days!.

[Leon Crampin]

The advantage of a zero Ohm resistor over a link is that they are supplied on a bandoleer and are handled by the same auto-insert heads used for other leaded components. Wire links take longer to assemble.

Leon.

[julie_m]

When I was working for an electronics manufacturer in the '90s, our auto-insertion machines could insert wire links cut from a (big) spool along with the VCD (double-ended) components. But some other manufacturers' boards that we sometimes reverse-engineered had resistor-sized links. So I guess it probably depends on the equipment used.

[frankmcvey]

Ah, so... I'm enlightened, thank you all!

[TonyDuell]

Before (I guess) there were zero-ohm resistors, HP (at least) used low value normal resistors for these selectable links. You'd have a TTL input that could either be connected to ground or to a 3k3 (or so) pull-up resistor via a 2.7 Ohm (don't ask me why they picked that value) resistor. I think the HP11203 interface was one place they did this.

As for the zero-ohm resistors, obviously these low-value resistors could be inserted automatically at the factory while bits of wire could not.

[electroanorak]

Zero ohm links are quicker than forming wire links. They also make a very neat job of things.

This is one of my prototype PCB's. On the close-up, I have ringed one of the zero ohm links.

Daniel.

[mikeei2dj]

Some years ago I got some from Farnell, may be worth checking with them to see if they still do them. How many are you looking for ?? If you let me know your address I could post you some.

Mike ei2dj / g4gxn

[frankmcvey]

Thanks very much for the offer, Mike, very kind of you. However, I don't need any - I asked the question because I couldn't think of a use for such a thing when plain copper wire is available. Being vintage myself, I hadn't considered that they might be more convenient for a machine to handle!

All the best,

Frank

[FrankB]

They are also often used on computer boards, that I have seen here.