Pressure Pro - Temperature Alert

[Jon Wehrenberg]

I am sure there is a place in today's world for algorithms. Apart from the fact they taste good if cooked properly engineers and technical folks are getting a little carried away in my opinion. As an example we have coolant level sensors. That's a pretty standard way to determine if there is coolant in the header tank. But in one of my cars the manufacturer has done away with that sensor and instead uses an algorithm that determines if the coolant level is sufficient, not based on measuring its absence or presence, but by doing calculations on how fast the car engine temperature rises. Obviously that is a complex calculation that has to take into consideration the outside temperature, how much power is being produced and a lot of other factors. My point is if it worked it would be great, but the car had to go back to the dealer 3 times because the message center was giving me dire warnings about coolant level. The dealer finally had to use a scorched earth method of fixing the problem and had to replace a whole bunch of items including the control head for the air conditioning system. But they saved the cost of s sensor in the header tank.

As to tires I am even more skeptical. If the sensors were internal I would be less so, but since they are external my first concern is the sensors are not even remotely getting exposed to the real tire temperatures. The length of the valve stem, the position of the tire, the external temps, the material of the wheel, etc. are all going to influence a temperature reading or calculation. Factor in the RPMs of the wheel and the valve stem sensor's position relative to air flow around the wheels and any temps the sensor and algorithms come up with are going to be inexact. Having said that, there will be a benefit. Treat the readings as meaningless, but pay attention to the normal pattern of temepratures. If the science behind the temperature readings is any good you should not care about absolutes in terms of the number, but you should care about deviation from the norm.

So to say 188 degrees is an upper limit is less valuable information than defining through observation what is a normal set of readings, and if that set of readings is a consistent pattern, then any out of the norm reading will be cause for further investigation regardless of what the raw numbers are.

[truk4u]

Pressure Pro can read the temps at any time by the operator, but the temp reading is at the sensor.

Here's their information on tire temperature and there was no link, so I have to just copy and paste. Sorry, it's lengthy.


Tire Temperature

PressurePro has been following the issue of tire temperature for over 15 years.* We are convinced that the attempts to make the pressure/temperature measurements FULLY accurate are elusive and we feel, possibly counterproductive. * To establish the temperatures that matter, the critical temperatures for Bias tires are 112C*and Radial 100C. The difference is that although the rubber compounds are relatively stable until 112, the bond strength between Nylon and Rubber (Bias) is better than between Steel and Rubber (Radial). In terms of a general comment, now that tires are predominantly radial, one would use 100 degrees (c) as the critical temperature. 200F is the temperature at which tire rubber compounds begin to scramble and damage occurs. When temperatures at the tire reach the 200F range, damage occurs to the tire. This heat is caused by several things: from speed, weight (when the tire’s side-wall stiffness is insufficient to support the load, extensive side-wall flexation will create excessive heat), brake problems, bearing problems, tire problems, alignment, brake fluid, etc. PressurePro is actually a terrific tool to gauge tire heat and when damage is being caused, and to allow maintenance to correct the wheel, tire, brake defect preventing higher costs and more damage.
*When you fill a tire with air, this becomes your base or reference pressure at that ambient temperature when the tire is cool and before use.* If the pressure goes up, you can calculate the temperature from the pressure rise (excluding tires that have a leak) or by using a compressor.* You will be able to determine leakers by a gradual loss in pressure with a tire management system (like enTIRE) that can track pressure changes over time OR a sudden loss of pressure via PressurePro readings.
It is inherently very complicated when measuring temperature, i.e. what temperature are you measuring? Do you measure the temperature of the carcass, or if so, where in the carcass do you measure - on the bead where it absorbs heat from the brakes and wheel or on the tread where most flexing occurs?**Do you measure the air inside the tire which would involve laminar flow analysis? A mistake made by many people is to assume that the air inside a tire is homogenous but it’s not. Simple fluid dynamics tell us this but it seems to seldom be considered. We find little agreement on where to measure and what the measurement means.

Heat surveys are done to understand operations at a site. It’s often done by the Tire Company that provides tires and maintains them. One will want to know the following: are there leakers, or has the tire gone flat, or is there excessive pressure building.* We take the practical approach in regard to pressures.* Firstly if they are filled to the correct pressure when cold, then that is the correct pressure. Pressure may increase temporarily due to speed, distance, etc but pressure and temperature will always come back down to the cold pressure or below when the tire cools. If ever it is necessary to take the sensor off while the tire is hot, the correct procedure is to wait till the tire cools, unscrew the Sensor, wait 45 seconds, and screw the Sensor back on. It has now used the correct cold pressure or reference pressure as the SET point to trigger from.

“Correct” method to inflate a tire initially is to inflate it & leave it sit for 24 hours, then recheck it and inflate/deflate as required. The tire will swell under initial inflation. As a rule of thumb, a larger 22.5” tire for trucks or RV’s normally takes 24 hours to return to ambient temperature and pressure after running.

If you need to check pressures in the field, when they are hot, you could use the temperature calculation to determine the cold pressure. A recommendation is to take the pressures of the tires on the same axle or close by to compare and fill the suspect tire to that level (or bleed air out). Check to see if they are similar in pressures or is one possibly leaking? This is where a Tire Management System comes into play, recording the history of each tire’s pressure over time so a trend can be spotted.
We believe a majority of tire problems can be recognized with this common sense approach. For the rest, having a monitored temperature system to compensate pressure at various parts of the tire, including all the electronics and batteries and communication issues would be hugely complex, expensive, and time consuming. We see more and more fleets today questioning the value of so much information vs. cost of that information.

This is just one reason the PressurePro system excels.* PressurePro is easy to install, simple to use, it’s reliable and accurate. PressurePro and a good management system can save money and make tires last longer and perform better. PressurePro is an excellent solution
Pressure increases in a tire due to temperature is dictated by gas laws as below. The gas laws are a set of empirical laws that describe the relationship between thermodynamic temperature (T), absolute pressure (P) and volume (V) of gases. They are a loose collection of rules developed between the late Renaissance and early 19th century. Three early gas laws:
Boyle's law (1662, relating pressure and volume): P1V1 = P2V2
Charles' law (1787, relating volume and temperature): V1 / T1 = V2 / T2
Gay-Lussac's law (1809, relating temperature and pressure): P1 / T1 = P2 / T2

These were combined to form the combined gas law


Furthermore, we don’t brag about our direct temp. reading from the externally-mounted Sensor on the valve stem, because it doesn’t really have a chance to be a very accurate reading of the internal tire temperatures from where it is directly located on the various lengths & types of valve stems which are in the sun, out of the sun, rained cooled & being air-draft cooled & not air-draft cooled, etc. Our estimated accuracy is approx. +/- 8 deg. F. (Of course our Chinese competition is joking when they are stating incredible temp. accuracy while also directly reading the temps. from the ends of valve stems.) The only way for Sensors to be accurate when located on the ends of valve stems, would be via thermo-couples located in tires using a wire connected to the Sensors via a pathway up the valve stem….which just isn’t viable. Therefore, since PressurePro uses very accurate GE pressure transducer chips and can usually be +/- 0.5 psi throughout a large pressure range, PressurePro augments its not-so-accurate direct temp. monitoring via offering an adjustable upper pressure alert capability (8 percentage settings between 10% & 45%). Tire pressures can very accurately predict temps, because the Charles & Boyles gas laws relate to temp. & pressure in a linear way. However, super temp. accuracy just isn’t a requirement for saving a tire that is over heating! The PressurePro factory ships all Monitors with a default upper pressure alert setting of +24%. This means that if the pressure of a vessel (tire) reaches a pressure that is +24% higher than its cold-running-pressure without the help of a compressor, we known that it has experienced a temp. of approx. 194 deg. F. This is a good time for the driver to stop and find out what is causing the increase in heat for his tire, because if the tire reaches 225 deg. F., the rubber chemistry will be modified to guarantee a very short tire life! It turns out that a tire increases in heat/temp.for only about 3 different ways. It can be inordinately under-inflated for the load it has to carry, whereby the side walls extensively flex to cause a lot of heat….or a brake caliper can hang-up to drag a brake pad or shoe to increase the heat (quite common)…or it can have a bearing self destructing (rather rare).

There will always be the argument that exact temperature readings are needed, but we believe, as are more and more experts, that as a practical matter this is not required. PressurePro alerts to high pressures which allows the driver/maintenance person to take action in a timely way. We believe strongly in concentrating on evaluating and monitoring tire pressures and forming decisions based on the axle, type of tire, construction of tire (bias/radial) and such, which often are ignored.


.

[rahangman]

Good info, Tom, and I thank you for being so diligent and precise, however, I also appreciate your "sorry" apology...sheesh is that bathroom reading or what?

[GDeen]

I am sure there is a place in today's world for algorithms. Apart from the fact they taste good if cooked properly engineers and technical folks are getting a little carried away in my opinion. As an example we have coolant level sensors. That's a pretty standard way to determine if there is coolant in the header tank. But in one of my cars the manufacturer has done away with that sensor and instead uses an algorithm that determines if the coolant level is sufficient, not based on measuring its absence or presence, but by doing calculations on how fast the car engine temperature rises. Obviously that is a complex calculation that has to take into consideration the outside temperature, how much power is being produced and a lot of other factors. My point is if it worked it would be great, but the car had to go back to the dealer 3 times because the message center was giving me dire warnings about coolant level. The dealer finally had to use a scorched earth method of fixing the problem and had to replace a whole bunch of items including the control head for the air conditioning system. But they saved the cost of s sensor in the header tank.

As to tires I am even more skeptical. If the sensors were internal I would be less so, but since they are external my first concern is the sensors are not even remotely getting exposed to the real tire temperatures. The length of the valve stem, the position of the tire, the external temps, the material of the wheel, etc. are all going to influence a temperature reading or calculation. Factor in the RPMs of the wheel and the valve stem sensor's position relative to air flow around the wheels and any temps the sensor and algorithms come up with are going to be inexact. Having said that, there will be a benefit. Treat the readings as meaningless, but pay attention to the normal pattern of temepratures. If the science behind the temperature readings is any good you should not care about absolutes in terms of the number, but you should care about deviation from the norm.

So to say 188 degrees is an upper limit is less valuable information than defining through observation what is a normal set of readings, and if that set of readings is a consistent pattern, then any out of the norm reading will be cause for further investigation regardless of what the raw numbers are.

Jon,

Good treatise on the computer age in general, and models to predict performance....

Keep in mind though that I am talking about the Smartire sensor, which is in fact banded to the inside of the tire on the OD of the wheel. It should get a much more accurate temperature reading than one that is spinning in the wind on a valve stem. It will be biased though by any heat fed through the hub assembly into the wheel I would think.

All the algorithm does is ensure that the PV=znRT equation is reflected in the increase/decrease in tire pressure with temperature. EG, as the wheel rolls and flexes and heats up, what is the expected increase in temperature and corresponding increase in pressure. An alarm is sounded if the change is outside of the predicted range, which I think is pretty good stuff.

We inflate tires to a cold rating at 60F because that is the benchmark. What pressure should correspond to 125F that is correct inflation at 60F? Is the tire experiencing excessive flexure and corresponding heat due to an underinflation that occured after you cold check pressure that morning from a nail you picked up? With multiple variables in play, I can't figure that in my head so it is nice to have a microprocessor figure it out and alarm you that something may be going wrong with your tires. That is really all we are talking about here.

As to the 188 degrees, my main point is that is their pre-set upper limit which I assume is based on some sort of data where one should become alarmed. The value is adjustable by the user, and I have changed mine as I have not seen temps anywhere near that high.

As an aside, one of my buddies is a PHD in EE and circuit design. He was showing me a sensor the other day that is about the size of a flake of glitter from one of Loc's club shirts that has a 3 dimensional accelerometer, temp sensor, and 24 bit microprocessor. Pretty incredible stuff. If you got'm, use'm....

[Sawbonz]

Off topic a bit now.....

I bought a cheap infrared temperature sensor to test tire temps. This will be new to me, but I picked it up on here.

How do I use it best? Where do you take the temperature? Is there a "normal" range? What else do I think about?

[merle&louise]

Jon,

Good treatise on the computer age in general, and models to predict performance....

Keep in mind though that I am talking about the Smartire sensor, which is in fact banded to the inside of the tire on the OD of the wheel. It should get a much more accurate temperature reading than one that is spinning in the wind on a valve stem. It will be biased though by any heat fed through the hub assembly into the wheel I would think.

All the algorithm does is ensure that the PV=znRT equation is reflected in the increase/decrease in tire pressure with temperature. EG, as the wheel rolls and flexes and heats up, what is the expected increase in temperature and corresponding increase in pressure. An alarm is sounded if the change is outside of the predicted range, which I think is pretty good stuff.

We inflate tires to a cold rating at 60F because that is the benchmark. What pressure should correspond to 125F that is correct inflation at 60F? Is the tire experiencing excessive flexure and corresponding heat due to an underinflation that occured after you cold check pressure that morning from a nail you picked up? With multiple variables in play, I can't figure that in my head so it is nice to have a microprocessor figure it out and alarm you that something may be going wrong with your tires. That is really all we are talking about here.

As to the 188 degrees, my main point is that is their pre-set upper limit which I assume is based on some sort of data where one should become alarmed. The value is adjustable by the user, and I have changed mine as I have not seen temps anywhere near that high.

As an aside, one of my buddies is a PHD in EE and circuit design. He was showing me a sensor the other day that is about the size of a flake of glitter from one of Loc's club shirts that has a 3 dimensional accelerometer, temp sensor, and 24 bit microprocessor. Pretty incredible stuff. If you got'm, use'm....

Lew would love this post!