109.3035 ohm resistor

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

retrolefty:

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

I see what you are saying but it looks to me like the minus numbers just apply to the minus temperatures at the top of the chart. Look 8 rows up from the 70 degree row.

Your right, I was too quick to see the structure correctly that changes between negative and positive values.

Lefty

retrolefty:
Your right, I was too quick to see the structure correctly that changes between negative and positive values.

Lefty

Easy mistake, Master Po. :slight_smile:

We had a good two hour talk with our vishay rep about these precision resistors, and got a sample card of different styles they make, its interesting stuff.

Like the ones we are using for production testing to act like shunts for current measurements (like single mA with 7 points of precision after that) are in a nutshell an array of resistors in series on a die which they fuse off to make different values.

those are the cheaper ones, like 20 bucks a pop (we ordered 100 of them, that was fun explaining to the purchasing dept "you spend 2 grand on 100 resistors!")

Yep it looks like a match i just don't see a $100 for a resistor to set that.But who no's Thanks for the math PapaG
I would use hot and cold. And thanks for posting this It sure been fun racking my brain. But maybe we should ask the suppler. LOL just to see whats what.

Osgeld:
We had a good two hour talk with our vishay rep about these precision resistors, and got a sample card of different styles they make, its interesting stuff.

Like the ones we are using for production testing to act like shunts for current measurements (like single mA with 7 points of precision after that) are in a nutshell an array of resistors in series on a die which they fuse off to make different values.

those are the cheaper ones, like 20 bucks a pop (we ordered 100 of them, that was fun explaining to the purchasing dept "you spend 2 grand on 100 resistors!")

I used some custom value Vishay parts in a product once. They can match temperature coefficients very closely so that if you use them in a voltage divider application the ratio tracks well with temperature. And yes, they can be a little spendy. :slight_smile:

be80be:
Yep it looks like a match i just don't see a $100 for a resistor to set that.But who no's Thanks for the math PapaG
I would use hot and cold. And thanks for posting this It sure been fun racking my brain. But maybe we should ask the suppler. LOL just to see whats what.

If you look at the data sheet for the part, http://www.mouser.com/ds/2/428/vhp100-10459.pdf, you can see that it has fantastic specs. It's probably more precise than any instrumentation you would have.

I enjoyed the puzzle as well. You can check with the supplier if you like. I'm convinced. :slight_smile:

It's probably the 'part number', misplaced in some SQL database, or put a couple in series, and get that 218.6070 ohm standard we're all looking for. haha.

PapaG:
The resistance of a PT100 sensor at 75 degrees Fahrenheit is exactly 109.3035 ohms.

But how do I calibrate my thermometer to 75F?

Chagrin:

PapaG:
The resistance of a PT100 sensor at 75 degrees Fahrenheit is exactly 109.3035 ohms.

But how do I calibrate my thermometer to 75F?

Substitute the resistor for the RTD and do what ever is appropriate to adjust your thermometer readout to 75F. Unless you describe your thermometer, I can't get more specific. An example of things to adjust would be to adjust the RTD current or the bridge amplifier gain.

Chagrin:

PapaG:
The resistance of a PT100 sensor at 75 degrees Fahrenheit is exactly 109.3035 ohms.

But how do I calibrate my thermometer to 75F?

Such a resistor is used to calibrate the interface electronics, not the sensor. You remove the sensor and wire the resistor in it's place. Once you have validated or adjusted the electronics to read 75F you remove the resistor and reinstall the RTD. That's it, the RTD is not adjustable, it obeys that resistance chart or it's defective. To validate the RTD after you have calibrated the electronics, you can just put it into boiling water and then an ice bath and see if reads out within the stated sensor accuracy specification.

Lefty

Well, I was implying that if it's spec'd at 109.3035R at 75F then you have to know when it's 75F if you expect it to be at 109.3035R (a circular problem).

As it turns out these types of resistor are accurate to 10 ppm from 15C to 50C so just having it at "room temperature" would be sufficient.

But "room temperature" isn't an objective measured value - it's a subjective assessed value