109.3035 ohm resistor

I was shopping for some precision resistors on Mouser's website and got distracted by the really high precision resistors. I found that there is a standard value in a Vishay part of 109.3035 ohms, 0.005% tolerance. That value seems to ring a bell some how but I can't dredge up any reasons for it. Does anyone know what the application of that value would be? It would be nice to have one but they are about $100 so I'm going to pass. :slight_smile: More common values in that precision are around $15-$20 in case anyone needs one.

PapaG:
I was shopping for some precision resistors on Mouser’s website and got distracted by the really high precision resistors. I found that there is a standard value in a Vishay part of 109.3035 ohms, 0.005% tolerance. That value seems to ring a bell some how but I can’t dredge up any reasons for it. Does anyone know what the application of that value would be? It would be nice to have one but they are about $100 so I’m going to pass. :slight_smile: More common values in that precision are around $15-$20 in case anyone needs one.

Well with a 0.005% tolerance ratings it’s useful just as a bench standard for calibration validation and such. But no, 109.3035 ohms means nothing to me. I’ve a few 250 ohm .01% resistors squirreled away. They were used to convert 4-20ma current loops to 1-5vdc measurement systems used in the process control industry.

Lefty

retrolefty:

PapaG:
I was shopping for some precision resistors on Mouser's website and got distracted by the really high precision resistors. I found that there is a standard value in a Vishay part of 109.3035 ohms, 0.005% tolerance. That value seems to ring a bell some how but I can't dredge up any reasons for it. Does anyone know what the application of that value would be? It would be nice to have one but they are about $100 so I'm going to pass. :slight_smile: More common values in that precision are around $15-$20 in case anyone needs one.

Well with a 0.005% tolerance ratings it's useful just as a bench standard for calibration validation and such. But no, 109.3035 ohms means nothing to me. I've a few 250 ohm .01% resistors squirreled away. They were used to convert 4-20ma current loops to 1-5vdc measurement systems used in the process control industry.

Lefty

Too strange a value to be a calibration standard, IMO. I guess I can email Vishay and ask. :slight_smile:

I suspect the value is a result of how the thing is engineered and manufactured. In other words, they strive for a certain range but the precise value is actually a side-effect.

That's a stretch. :slight_smile: Are you saying that they were shooting for, say a 110 ohm and got this value? And, they are so good at producing this wrong value that they assigned it a part number and sell it for 5 times the rate of the 100 ohm? Great marketing! Not only that, it is guaranteed to be this weird value to 0.005% error and to have a 0.2ppm temperature coefficient and is supplied in a hermetically sealed package which is either, your choice, oil filled or air filled!? All its siblings in the series have values like 100, 130, 200, 400, 500, 1000, ... By the way, you can order a special value to the 0.005% tolerance but all the possible values are not listed in the Mouser catalog. No, I think a 109.3035 ohm, very precise, very stable resistor has some application that I don't know about.

Aha! I figured it out. Is anyone curious? :slight_smile:

Say on.

The resistance of a PT100 sensor at 75 degrees Fahrenheit is exactly 109.3035 ohms. So, if you want a handy way to calibrate your instrumentation, a very precise, very stable, resistor of that value is just the ticket! :slight_smile:

PapaG:
Are you saying that they were shooting for, say a 110 ohm and got this value?

No. I'm saying they were shooting for approximately 100 ohms. After meticulous design work they determined that the final value would be precisely 109.3035.

I worked with a state-of-the-art gas analyzer where something similar was done. Nothing existed that could be used to test or verify the accuracy of the meter. The accuracy had to be determined entirely on paper (with some finger-crossing by the secular and praying by the faithful).

PapaG:
Now that's interesting. Anything we should be worried about if everyone was wrong? :slight_smile:

Most certainly! The analyzers are used to deliver ultra-pure nitrogen to Texas Instruments for chip fabrication. Millions of little lives are on the line!

Now that IS serious! I'm crossing my fingers too!

Too strange a value to be a calibration standard, IMO. I guess I can email Vishay and ask.

Ah but grasshopper you must free your mind from such thinking. A resistance standard is anything that you have belief in it's stated accuracy, and willing to pay to own such. Such a resistor wired to your hot shot ohm meter should tell you if your meter needs calibration or not, that is all that is involved in validation. If your ohm meter doesn't agree, you don't go buy another resistor standard to adjudicate the discrepancy, you (or someone) adjusts the meter to agree with your standard. A resistance standard is a standard no matter what it's specific value is.

Lefty

retrolefty:

Too strange a value to be a calibration standard, IMO. I guess I can email Vishay and ask.

Ah but grasshopper you must free your mind from such thinking. A resistance standard is anything that you have belief in it's stated accuracy, and willing to pay to own such. Such a resistor wired to your hot shot ohm meter should tell you if your meter needs calibration or not, that is all that is involved in validation. If your ohm meter doesn't agree, you don't go buy another resistor standard to adjudicate the discrepancy, you (or someone) adjusts the meter to agree with your standard. A resistance standard is a standard no matter what it's specific value is.

Lefty

Ah, so true, wizened old monk. :slight_smile:

The substance my components occasionally release doesn't smell like ultra pure nitrogen. You botched something up.

Where did you find that a PT100 is 109.3035 It's 109.73 at 25C could you show how you did the math for Fahrenheit

be80be:
Where did you find that a PT100 is 109.3035 It's 109.73 at 25C could you show how you did the math for Fahrenheit

Try 65 degrees F = 109.304 ohms from chart:

Lefty

I been racking my brain about this and I no I seen these things used in some thing just don’t no what it was
But I don’t think it’s to set for 75 F cause it didn’t add up on any chart I seen.

be80be:
Where did you find that a PT100 is 109.3035 It’s 109.73 at 25C could you show how you did the math for Fahrenheit

Well:

25 * 9 / 5 + 32 = 77 degrees F

(75 - 32) * 5 / 9 = 23.9 degrees C

From the chart at http://www.tnp-instruments.com/sitebuildercontent/sitebuilderfiles/pt100_385f_table.pdf :

77 degrees F = 109.735 ohms
75 degrees F = 109.304 ohms

It all looks right to me.

PapaG:

be80be:
Where did you find that a PT100 is 109.3035 It's 109.73 at 25C could you show how you did the math for Fahrenheit

Well:

25 * 9 / 5 + 32 = 77 degrees F

(75 - 32) * 5 / 9 = 23.9 degrees C

From the chart at http://www.tnp-instruments.com/sitebuildercontent/sitebuilderfiles/pt100_385f_table.pdf :

77 degrees F = 109.735 ohms
75 degrees F = 109.304 ohms

It all looks right to me.

I think your misreading the chart. You look at the 70F row and move 6 columns (-5) right to reach 65 degrees = 109.304 ohms.

Lefty