I have a resistor which is 5 gigaohm according to its color bands, but when I measure it, it shows me 1 ohm. I tried to find 5 gigaohm resistors online but couldn’t find anything.
Does it really exist?
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16\$\begingroup\$ How do you get 5 G Ohm? Silver in the 3rd band should be x 0.01 \$\endgroup\$– NeddCommented Jan 26 at 6:29
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9\$\begingroup\$ @Nedd Probably by mistaking that silver for grey \$\endgroup\$– TooTeaCommented Jan 26 at 7:23
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9\$\begingroup\$ That's not a 5 gigaohm resistor according to the color bands. The colors are green-blue-silver-gold, so it is a 0.56 ohm 5% resistor. Now, for the actual question, what are 5 gigaohm resistors used for and do they exist, I won't answer as it might be irrelevant since that resistor is not a 5 gigaohm resistor. \$\endgroup\$– JustmeCommented Jan 26 at 8:50
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3\$\begingroup\$ Should we answer the question title only whilst ignoring the context, or should we answer based on the fact that the resistor shown is not actually 5 gigaohms? \$\endgroup\$– Rohat KılıçCommented Jan 26 at 15:06
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1\$\begingroup\$ IIRC, some power supplies include very high-impedance resistors across their very high-voltage and high-capacity capacitors in order to make them safer by discharging them safely during off time so that they're safer to maintain (maybe?). \$\endgroup\$– GallifreyanCommented Jan 26 at 17:04
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8 Answers
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Color bands on resistors vary widely, colors can be deceiving at times. The band spacing may not be as expected. There can be 3 to 6 bands altogether.
The color code on the part you have sure looks to be Green, Blue, Silver, Gold.
I would read it as 56 x 0.01 at 5%, (or 0.56 Ω).
Your measurement seems to be fairly close to confirm such a low value.
Also note that your meter leads could have a few added tenths of an Ohm off-setting the measurement. If the value is critical use a better quality Ohm meter that incorporates an Ohm zeroing function. As an alternative you could select the lowest ohm setting on your meter, short the leads, read the offset due to the wire leads, measure the resistor, then subtract out the offset reading from the resistor reading.
For reference here is a some-what standard resistor color code chart.
Resistors in the giga Ohm range while not common can be used for example to limit current in very high voltage circuits, create wide range voltage dividers, provide a leakage path for high voltage capacitors, created ultra low currents for precision measurement or references, (additional uses are given in some of the other comments and answers).
But as noted above the component shown in the original photo is not a giga Ohm resistor.
As a visual example here are glass encapsulated 5.6 GOhm resistors available for purchase:
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The above image is from this web page.
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6\$\begingroup\$ I gave it an upvote because, while it didn't answer the question directly, it did provide a relevant piece of information that may be useful to others - stare long and hard at the color bands. \$\endgroup\$– SteveShCommented Jan 26 at 13:08
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4\$\begingroup\$ @SteveSh Sometimes a person writes a question that is not their actual question. Rather than pedantically answering what they wrote, it is best to answer their actual question. \$\endgroup\$ Commented Jan 26 at 15:02
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1\$\begingroup\$ Yeah, I see your point. But in general, I don't downvote unless the answer is clearly wrong or is totally off base. \$\endgroup\$– SteveShCommented Jan 26 at 15:41
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10\$\begingroup\$ @MCG This answers OP's real question... "Why is this resistor I found used reading 1 ohm instead of 5 Giga ohms like I think it should" \$\endgroup\$– QuestorCommented Jan 26 at 21:05
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3\$\begingroup\$ I'm with @Questor. It's an "X Y" question. \$\endgroup\$– gbarryCommented Jan 26 at 21:11
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What are 5 gigaohm resistors used for?
I used a 5 GΩ resistor at low voltages in the feedback path of a transimpedance amplifier, in order to measure pA and fA currents easily.
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1\$\begingroup\$ How was the noise on your reading? \$\endgroup\$ Commented Jan 27 at 0:30
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4\$\begingroup\$ @MisterMystère I don't remember exactly, but it was ~10 fA/rtHz. Of course you also need an op-amp with correspondingly low input current noise. \$\endgroup\$– tobaltCommented Jan 27 at 7:27
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2\$\begingroup\$ better not look at the system under test lest your eyeballs throw some extra electrons at it \$\endgroup\$– Bryan BCommented Jan 27 at 19:25
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3\$\begingroup\$ @BryanBoettcher the (by far) dominant error source for these measurements were mechanical vibrations due to people walking by, doors, or even typing on the keyboard etc. They lead to vibrations of the cables, which release triboelectric charge. \$\endgroup\$– tobaltCommented Jan 28 at 7:05
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1\$\begingroup\$ i.e. it's best to build such thing without cables between DUT and the transimpedance amplifier \$\endgroup\$– tobaltCommented Jan 28 at 7:15
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Resistors in the 100 megaohm to many gigaohms are common in high voltage probes. In some cases a pair of them are used to take a differential reading to measure current when the common-mode voltage could be 20 kV to 100 kV. CADDOCK makes such resistors on a hard ceramic plate, at a hefty price.
I used 500 megaohm .025% tolerance resistors at $75 each to measure milliamps of current on lines with a 30 kVdc common voltage.
In extreme cases capacitor dividers (for ac power) or long chains of ceramic resistors are used on 100 kVdc supplies. It depends on the industry you are in, and what your budget is.
I should clarify that my answer was based on a question about 5 gigaohm resistors, which is not what is shown. This requires another answer of which many have been posted.
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9\$\begingroup\$ Another use for such high value resistors was in older Geiger counter circuits that used high voltages and a large Geiger-Muller tube. The parts I came across while repairing an old unit were a few G Ohms and were fully glass encapsulated to reduce contamination and leakage. \$\endgroup\$– NeddCommented Jan 26 at 7:05
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I tried to find 5 gigaohm resistors online but couldn’t find anything.
The largest value I've seen in a "normal" looking through-hole resistor with colour code bands is 1GΩ. Resistors larger than that exist but all the ones I can find don't look like regular resistors.
For example mouser sell a 5GΩ throughole resistor https://www.mouser.co.uk/ProductDetail/Vishay-Techno/TR10X5G00JNES?qs=sGAEpiMZZMtlubZbdhIBIGN9apd1LfqHmvlVzG7A2MY%3D but it looks nothing like a normal resistor.
I have a resistor which is 5 gigaohm according to its color bands, but when I measure it, it shows me 1 ohm.
As others have said, it looks like you have misread a silver band as grey.
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\$\begingroup\$ Also the OP could use a better DVM. 1 ohm of resolution is poor by today's standards, adding to the confusing results. \$\endgroup\$ Commented Jan 27 at 0:05
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1\$\begingroup\$ @Sparky256 How do you know it has 1 ohm resolution? The measurement is likely not resolution limited, 0.56 ohm is well in the size range of probe contact resistance+2xlead resistance. \$\endgroup\$– MrGerberCommented Jan 27 at 13:41
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1\$\begingroup\$ My experience is that measuring sub 1 ohm resistances with a 2-wire multimeter is an exercise in frustration. Even if the meter has the resolution and even if you try and subtract the resistance of the leads the readings never seem very stable. "Low-ohms" meters used by electricans use higher test currents, which seems to reduce the issues. \$\endgroup\$ Commented May 10 at 19:49
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It's a low value 0.56Ω resistor, probably a current sense resistor, as others have pointed out. Sometimes resistor color bands can be difficult to read, especially if the part is faded or has overheated, but your photo of this one is crystal-clear.
A possible application is as part of a divider to measure high voltage without wasting too much power. Some battery-powered devices that require high voltage are Geiger–Müller tubes and image intensifier tubes. They have applications in scientific equipment where they operate in a vacuum and/or cryogenic environment. You might just want to leak off any accumulated charge in a reasonable time without caring too much about the current except that it should be small. A 5GΩ resistor and 100pF (roughly the capacitance of human body) has a time constant of 0.5 second.
If you want to measure pA range currents, a high value resistor will drop a reasonable voltage which you can then measure using an appropriate amplifier. A 5GΩ resistance will drop 5mV at 1pA.
There are a fair number of SMT 5GΩ and higher value resistors available, such as Stackpole's HVC high voltage series, available up to 50GΩ as standard. Digikey has more than 500 pieces of 2512 (SMT) 500GΩ resistors in stock, rather amusingly rated at 2W. Here is one popular application for such high value resistors:
My ancient Fluke 8026B multimeter has a range of 200nS full scale, with a resolution of 0.1nS (and it really does read 0.0 with the input open) so it should read about 0.2 with a 5GΩ resistor. Not a great measurement but it will tell you it's there.
To get good results with resistances in the GΩ range you may need guard rings, lifted chip leads connected to PTFE standoffs and that sort of effort to minimize leakage effects. .
answered Jan 26 at 18:03
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1\$\begingroup\$ @DavideAndrea The 10MΩ is just for protection, think of it as a short circuit (which it is compared to 500GΩ!). A 1pA current flowing into the input will result in -500mV at the output. At full scale +/-10pA input current the 10MΩ is dropping only +/-100uV. So the input terminal is almost at ground (the amplifier Vos will have an effect though). \$\endgroup\$ Commented Jan 26 at 19:04
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1\$\begingroup\$ Hey Spehro, nice answer as usual. I am curious about the "rather amusingly rated at 2W." - why do you say this is amusing? I figured you meant that for such high values resistors, power rating is irrelevant, but you can achieve that with a couple of uA. Granted, you'd need 1 MV... Perhaps your point is that they will arc before they fail for power? I am just confused is all :D \$\endgroup\$ Commented Jan 28 at 7:14
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2\$\begingroup\$ @VladimirCravero Exactly! To get to 2W you'd need 1MV across the ends of the (3kV rated) 500GΩ resistor which sounds very exciting. The maximum power dissipation (limited by voltage rating) would be a mere 18 microwatts. \$\endgroup\$ Commented Jan 28 at 13:22
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1\$\begingroup\$ Perhaps the power rating is just the standard for that package. Or perhaps it's a challenge... \$\endgroup\$ Commented Jan 28 at 13:44
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Condensor microphones used in sound recording often uses 1GOhm resistors (not quite 5G Ohm though).
Example here, R1 and R11: http://edge.rode.com//pdf/products/13/broadcaster_product_manual.pdf
Or the classical U87 *), R6 and R7: http://recordinghacks.com/microphones/Neumann/U-87
*) The U87 has had several iterations of the circuit, but as far as I know there is always 1G Ohm resistors for biasing the condensator membrane.
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Obviously, the resistor shown is not 5 GΩ, as already mentioned by others. I believe the resistor is salvaged from a power supply and is used as a current sense resistor.
As for your main question, which is what could be the possible use of such a high resistor, I personally have never needed or come across such high resistance so no specific application comes to my mind.
But I remember that the Turkish Scientific and Tech Research Council used to work on (or design) a piece of equipment that was supposed to measure up to some TΩ (teraohms) resistances. That equipment should employ gigaohm resistances: Different resistor bridges formed by resistors in different scales (e.g. 100 MΩ, 10 GΩ, etc) could be relayed separately during measurement.
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5 gigaohm resistors can be used for shunts in some lines.
I have worked with more than 4 million VoltAmp lines and they can have big shunts used with them for analytics of the line, so from 1.5 volt to high voltage a variety of sensors might use a variety of resistor sizes.
