How accurate?

[Don S.]

The post below about tire pressure reminded me of a question I have long had.

How do you know that the tire pressure guage or thermometer are accurate? Particularly in the case of thermometers; several on a rack in a store,temps vary by several degrees. Is it 68 or is it 72 in the store? Is it 35 lbs., or is it 37 lbs?
 

[the tractor vet]

well the three tire gauges i have i know that they are a accurate as the test gauge that they were tested on , as i got mine right out of where they are made and they tested them before they handed them to me as i was watching them do this and tested five before they handed me the three that tested good and threw the other two in the scrap bin.
 

[PJH]

Store thermometers are interesting. I always just compare them and pick one that agrees with most of the others on the rack. There'll always be an oddball. Don't bring it home, ha. Now if you're into critical temps, you can swill your new thermometer around in a glass filled with crushed ice and water and it should read 32F. Or a pan of boiling water and it should read 212F. You'll have to pay for it first. I used thermometers a lot before I retired, and I'd periodically test mine (and adjust, if needed). Of course that was back in the dark ages. Now they probably have something that they point and it speaks the temp to you.

Tire guages? Never gave them much thought. Now you've got me wondering. I've got three or four and I'm gonna compare them, not that I'll know anything when I'm done.
 

[Walt Davies]

HA! Don't have to worry about my tire gage it's US Goverment tire gage even has the Goverment part umber on it.
Actually is a very good gage as it will test over 100 lbs.
Walt
 

[Ultradog MN]

I'm curious what elevation you were at and what was the temp you adjusted your thermometer to.
boiling points at various elevations.

 

[c.hess]

To be sure of the accuracy by testing the therometer in boiling water you will first have to have a accurate barometer an know if the pressure is at 15.9psi. Any pressure other than that will cause boiling temperature to vary.
 

[jimlll]

I find the same problem (different readings) with volt meters, pressure gauges and thermometers, etc.
You can calibrate a pressure gauge by gauging the pressure of a propane cylinder etc but you have to know the actual temperature of the propane, and barometric pressure, so theres the problem, how do you know with the differences in thermometers and barometers.
 

[PJH]

Well - it's 560 ft above sea level here in front of the kitchen stove. The temp I used was 212 degrees. They were Taylor stem thermometers that I used to check hot asphalt, and they had 10 degree incremental markings. The spec range was 250 - 350 degrees, so I only had to know that they were tolerably close. They kinda took a beating being repeatedly jammed into a load of asphalt.
 

[Janicholson]

No flame just fact ---- the atmospheric pressure 760 mm Hg (torr), 29.92 in Hg, 14.696 psi. sea level! Jim
 

[PJH]

By the way UD - thanks for the link. I bookmarked it.

Paul
 

[MarkB_MI]

Tire gauges are notoriously inaccurate. I have a 35 year old Draeger gauge, made in Germany, that is dead on. When I buy a new gauge, I compare it with the Draeger. If they don't agree the new gauge goes in the trash. I bought a "Slime" brand gauge at AutoZone a while back that was off by over 5 psi.
 

[wisbaker]

We had one of the dispatchers in the 911 center complaining about it being too cold when she worked, she knew it was cold because her little bi-metal thermometer said it was cold. Boy did she have a cow when my maintenance guy pulled out his little pocket screw driver and "tweaked" her thermometer to match the thermocouples in the HVAC system. On better quality instruments there is a calibration process. In the Air Force all our meters, thermometers and torque wrenches had to be regularly calibrated and when ever they were dropped or over ranged, torque wrenches any time the scale was moved below zero.
 

[Ultradog MN]

Ahh,
Hot asphalt - not such a big deal.
Now if you were making carmels for the grand kids you'd want to be more accurate
 

[c.hess]

Opps i was thinking about my post later an realised i was incorect about pressure .I stand corrected!
 

[jackinok]

common way of checking a thermometer or themocouple is to place it in a glass of ice water. should read 32 degrees.