Pressure around
Air pressure (atmospheric pressure) in any unit area on the surface of the air pressure generated by molecular motion. Is usually measured by a high degree of cross-sectional area of units at and above the weight of the vertical atmospheric column
(1) the definition of gas pressure
Role in vessel wall of gas pressure on the unit area is the gas pressure.
p=F/S p = F / S
(2) gas pressure causes
From the molecular kinetic theory we can see that the gas pressure is frequently a large number of molecular collisions arising from the container wall. A single molecule of the vessel wall collision time is very short role is not continuous, but a large number of molecular collision frequency wall, right wall of the force is a continuous, uniform, this pressure and the ratio of wall area is the pressure of the size of .
(3) The unit of pressure
International System unit: Pascal, abbreviated Pa symbol Pa.
Common unit: standard atmosphere.
1atm=1.013×10^5Pa=760mmHg 1atm = 1.013 × 10 ^ 5Pa = 760mmHg
(4) The method of calculating pressure
Equilibrium conditions are usually law and Newton’s laws of motion method (the formula is only a rough calculation, and sometimes the values measured are not allowed, all should be based on the actual date).
The size of air pressure and altitude, air temperature, atmospheric density, is generally higher with a high degree of exponential decline. Pressure with diurnal and annual variation. One year, the high pressure in winter than in summer. One day, the pressure has a maximum value, a minimum value, respectively, in 9 to 10 am and 15 ~ 16 o’clock, there is a second high-value and a second low-value, respectively, in 21 to 22 am and 3 ~ 4 pm . Diurnal variation of atmospheric pressure to a lesser extent, generally 0.1 to 0.4 kPa, and decreases with higher latitude. Pressure changes and wind, the weather is good or bad and so close, so it is important to meteorological factors. Commonly used pressure units Pa (Pa), mm Hg higher (mm · Hg), millibar (mb). The conversion relationship between them as follows: 100 Pa = 1 mbar ≈ 3 / 4 mm Hg higher. Commonly used in meteorological observation instrument measuring atmospheric pressure with mercury barometer, air box barometer, barometer. 101.325 kPa pressure (760 milli-Migon column), known as the standard atmospheric pressure, which is equivalent to the acceleration of gravity is 9.80665 meters / sec 2, the temperature is at 0 ℃ 760 millimeters of mercury column vertical high pressure, standard atmospheric pressure, first from Italy Scientists measured Tory split profits.
Related words:
Barometer: Measuring air pressure equipment, the most common are mercury barometer and the two kinds of empty boxes barometer. Several instruments are more accurate …
Digital Tire Pressure Gauge
The original Roadgear “Hi-Tec” tire pressure gauge was (and still is) a popular “must have” item for motorcyclists. Roadgear has probably sold a zillion of them to motorcyclists around the world. Its light weight and unique shape make it an ideal accessory that can be carried under the smallest of seats.
But time marches on, and Roadgear’s newest iteration of the device is so small and light that it brings to mind comparisons like Chihuahua vs. Bulldog, finishing nail vs. railroad spike or Ford Ka vs. Excursion. You get the idea…
The original version of the gauge is 155mm (6-3/32″) long, and the handle was 18mm (~11/16″) thick and 37mm (~1-1/2″) wide. It weighed in at 46 grams, or 1-5/8 oz. Certainly not a heavyweight, by any stretch of the imagination. But the slim new model really does make the old one seem quaint. The new design weighs in at less than half the original, at 21 grams (3/4 oz.). It’s 139mm long, and the thin oval shape is only 17mm (~11/16″) wide and 15mm (~9/16″) thick.
Not only is it lighter and smaller, it has more features — it includes a tire tread depth gauge! The and opposite the valve has a retractable tread depth gauge, calibrated in millimeters and inches. It will measure from 0 to 20mm or 0 to 3/4″.
The older design had a bend in the body near the head, which made it easier to fit under a motorcycle wheel’s brake rotor on many different tire/wheel/disk brake configurations. It was a
breakthrough design in tire air pressure gauges because of this shape. The new design is so much thinner that this really isn’t an issue. If you can’t fit this gauge on a tire’s valve stem, there’s probably no way you’re going to fit an air compressor valve stem fitting on it anyway.
The shape of the valve stem adapter has also been revised on the new design. We never really had any problems with the old design, and we found that it was relatively easy to fit it over a tire valve stem, enabling the user to get a pressure reading without losing much air from the tire. The new design has a round head with what seems to be much closer tolerances, and it fits very easily and snugly on to the tire’s valve stem, making it easy to get a reading without losing any excess air at all. It does seem to require just the right angle and pressure to get a reading though, but it doesn’t take long to find the best approach.
To bring a motorcycle tire up to the correct pressure, it’s usually best to add a few pounds more than is required, and then bleed off the excess until the desired reading is attained. Some users complained about the older style gauge, because it didn’t provide the ability to bleed off the excess air. But I found that it was easy to bleed off air using the old style simply by pressing it lightly on the valve stem, just like taking a reading but without pressing all the way down.
It doesn’t take much time at all to lose a pound or two from a (relatively) narrow motorcycle tire, so this method worked for me. The new gauge has a valve depressor nub on the back of the head, which is the recommended method to relieve the pressure. I still find it easier and quicker to apply light pressure without flipping the gauge over, but the choice is yours.
The only downside of the new gauge is that the digital readout ends up being located on the back side, which is then 90 degrees from the line of sight if the tire valve stem is perpendicular from the ground. The old gauge has the readout on the left side, so if you’re right handed, you could take the reading and see the results without having to flip the gauge.
This was helpful, especially if the gauge wasn’t precisely centered on the valve stem, which can result in an erroneous reading, usually designated by “0.00″ on the readout. If the tire is rotated until the valve stem is at the bottom of the tire, pointing straight up, the new style gauge can be positioned so that the digital readout will be pointing straight up, making it easier to see.
Otherwise, the new gauge requires that you take the reading, take the gauge off the stem, flip it sideways to view the smaller readout, then put it back on the valve stem. It gets a bit more complicated if you have to flip the gauge over to use the valve depressor nub to bleed out some air.
In any case, it’s much easier than it sounds, and it’s probably not a big deal unless you’re very used to using the old system. We occasionally run into some balkiness if the second reading is taken too soon after the first, where the gauge will give the “0.00″ error reading.
The newly revised Roadgear digital tire pressure gauge will read from 5.0 to 99.5 psi in half-pound increments. Roadgear claims that it’s accurate to ± 1% (e.g., ± 0.4 psi on a 40 psi tire), and they offer a nifty five-year warranty. The new gauge (like the old one) has a lifetime battery. Isn’t modern technology wonderful?
Remember that having the correct motorcycle tire air pressure is extremely important. As we mentioned in the original review of the Roadgear tire pressure gauge, motorcycle tires are very sensitive about correct tire pressures, partly because there is a correlation between the contact patch and the tire’s pressure; other reasons involve the way the tire’s internal reinforcement will cause heating and cooling cycles that may be affected by internal pressures. The bottom line is that changes in tire pressure can have dramatic effects on handling, braking and traction.
Improper tire pressures can also affect tire wear. Roadgear’s website has some numbers that indicate a 30% reduction in tire pressure can reduce tire life by 48%. Although a 30% reduction is pretty dramatic, and I would guess that webBikeWorld visitors would never ride their bikes with such under-inflated rubber, the point is still valid, especially considering the cost of motorcycle tires. Even a few PSI less than required can change the wear characteristics of tires.
The lesson here is that it’s really important to check your bike’s tire pressures before every ride. The valve stems on some motorcycle wheels can be hard to access, and it’s easy to tell yourself you’ll do it next time. But tire pressures should be checked before every ride.
The Roadgear Digital “Hi-Tech” tire pressure gauge costs about twice as much as a good quality pencil type gauge, but its light weight, stealth black grippy finish, accuracy and cool nylon carrying case make this one accessory that’s too cool to ignore.
New style gauge has thinner, narrower profile.
New gauge has a tire tread depth gauge on the flip side.
- Old style gaugeNew style gauge has thinner, narrower profile.
Old vs. new style Roadgear Digital Tire Pressure gauges.New gauge has a tire tread depth gauge on the flip side.
Based on MCS Control Design and Implementation of Digital Pressure Gauges
Abstract: This paper introduces a precise digital pressure gauge of hardware and software implementations. The method with atmospheric pressure through the pressure sensors, the corresponding analog voltage value, and after V / F transform input to the microcontroller for processing to real-time display the corresponding pressure values. Using the method described in this article digital pressure gauge made and easy to carry, simple operation, high accuracy, full compliance with design requirements.
1. Introduction
Pressure Gauge is the use of pressure-sensitive device under test pressure will be directly transformed into easy detection, transmission of current or voltage signal, and then through the subsequent processing circuitry and real-time display of a device. The core component of which is the air pressure sensor, which monitors the pressure in the size, control pressure changes and physical parameters of the measurements plays an important role. Digital pressure gauge of the pressure sensors used are basically relying on the pressure changes of different heights to get the pressure value.
Meteorology studies have shown that in the vertical direction, atmospheric pressure decreases with height increase. For example, in low-rise, each rising 100m pressure to lower 10hPa; in 5 ~ 6km of high-altitude, height for each additional 100m, pressure will be reduced 7hPa; and when a high degree of further increases, that is 9 ~ 10km altitude, the height of each additional 100m, pressure will be reduced 5hPa; Similarly, if there was a downward air flow, the pressure will increase; if there is an upward air flow, the role of the air column at the bottom of the air pressure is reduced. General to act on the unit area on the weight of the air column is called atmospheric pressure
2. The Structure of Digital Pressure Gauge
One pressure sensor is used to convert the measured pressure voltage signal; with the V / F converter can put pressure sensor output voltage signals into a certain frequency pulse signal; in order to use microcontroller to receive the pulse signal and in accordance with per unit time within the pulse number, voltage and frequency based on a linear relationship to calculate the pressure corresponding to the value, in the end MCU controlled by the LED display.
The digital pressure gauge of pressure sensor can be accurately measured within the linear range of the corresponding pressure values. Be explained is that its measured value is the absolute pressure values. Digital pressure gauge of this study the technical indicators are as follows:
● measuring range: 300hPa ~ 1050hPa;
● Accuracy: 0.1% FS (20 ℃);
● Display accuracy: 0.1%, from four 8-segment LED display of;
● Operating temperature range: 0 ~ 85 ℃;
● Supply voltage: 9V.
3. System Implementation
In the system building process, the need to consider the stability, complexity, cost and ease of debugging and other factors. Modules there is no complex signal transmission, and interference with very little, so overall system more stable.
Pressure Sensors
Digital pressure gauge of pressure sensor in the central position occupied. Designed according to measurement accuracy, measuring range, temperature compensation for measuring absolute pressure values, and several other performance indicators to select the air pressure sensor.
As the digital pressure gauge shows the absolute pressure values, and therefore need to select the value of the pressure measuring absolute pressure sensor. Meanwhile, in order to simplify the circuit, improving stability and anti-jamming capability, requested that the air pressure sensor with temperature compensation should be.
To this end, I use Motorola’s MAX4100A pressure sensor to measure the absolute pressure values. The sensor temperature compensation range of -40 ~ +125 ℃; pressure range of 20kPa ~ 1050kPa; output voltage signal (Vs = 5.0V) range of 0.3 ~ 4.65V; measurement accuracy of 0.1% VFSS, at the same time In the 20kPa ~ 1050kPa good linearity when the specific output relationship is as follows:
Ｖｏｕｔ＝Ｖｓ(０．０１０５９ Ｐ－０．１５２８) Vout = Vs (0.01059 P-0.1528)
Japan launched a long-term stability of the Vaisala excellent Digital Pressure Gauge
Vaisala (Vaisala, Headquarters: Tokyo) launched in April 2008 Digital Pressure Gauges “PTB330″. Determination of the range of 50 ~ 1100hPa, or 500 ~ 1100hPa. High-precision models can ± 0.15hPa accuracy determination. A year’s average error of ± 0.10hPa. Request for determination of accuracy and long-term stability of the industrial and aviation use. Specifically, high-precision measurement can be used to want to pressure of the occasion, such as using laser interferometer for measurement, as well as the engine testing in the exhaust gas analysis.
Products that can be embedded in a ~ 3 silicon capacitive absolute pressure sensor “BAROCAP”. If you use multiple sensors, pressure gauges, the determination of the value of the sensor can be compared with each other to determine whether the differences in the set of its range. In this way, can improve the reliability of measured values to easily grasp the pressure gauge to maintain and re-calibration date.
Measurement data not only to a numerical display, but also in order to observe trends in the charts. Chart in the observation process can be automatically updated. The use of special software, you can achieve data transfer to the PC.
MANUFACTURING STEPS OF THE SECOND GENERATION PROTOTYPE
MANUFACTURING STEPS OF THE SECOND GENERATION PROTOTYPE
Construction Details – Second Generation Prototype
To simplify the design, the miniature connector between the main board and the sensor board was removed. The interconnecting wires are directly soldered to both boards and the hole is sealed by silicone rubber. To cut cost, the main PCB is held in position by glue rather than a screw and a battery with pins was used in place of the battery holder. The mechanical construction of the improved design is shown under.
Mechanical Construction (Top and Bottom View)
The photographs of the actual PCB are shown under.
Prototype PCB of the Improved Design (Top and Bottom View)
The photographs of the assembled gauge are shown under.
Assembled Tire Pressure Gauge with and Without the Front Plexiglass
Bill of Materials – Second Generation Prototype
| Item | Quantity | Reference | Part |
| 1 | 1 | BT1 | CR2032, 3 V Lithium |
| 2 | 2 | C4, C5 | 100n |
| 3 | 1 | D1 | LCD, 23 x 1 Segments |
| 4 | 1 | J1 | Connecting Wires and MPXY8020 |
| 5 | 3 | J2, J3, J4 | Headers for Debugging |
| 6 | 1 | SW1 | Push Button |
| 7 | 1 | U1 | MC68HC908GT8 |
Schematics – Second Generation Prototype
The initial prototype used an LCD display targeted for a low–cost digital watch. Testing of the prototype revealed that the larger display should be used for improved readability. Since the design was not meant for mass production, ordering a custom made LCD display was not adequate and the design had to use an industry standard LCD display. The display which was chosen does not use the multiplexed driving scheme and therefore requires a higher number of I/O pins. To match this requirement, the MC68HC908GP32 microcontroller was chosen and later exchanged for pin compatible MC68HC908GT8 which features an internal clock generator unit and does not require an external crystal. The schematic diagram of the redesigned application can be seen under figure.
Digital Tread Depth Gauge Tittle-Tattle
Unless you work with tires all day there’s probably no need for you to add Central Tool’s digital tread depth gauge to your toolbox. You could probably get by with a set of digital calipers, a ruler, or a penny for that matter.
If you take away the wide base and the 1″ maximum depth, these stainless steel digital calipers look exactly like the cheap calipers you find on eBay or Harbor Freight with pretty much the same functionality. Some retailers claim this gauge displays fractions as well as inches and millimeters, but looking at the display we doubt it.
You’ll pay somewhere between $25 and $35 for this digital tread depth gauge.
CONSTRUCTION DETAILS
Since the MPXY80xx family sensors perform absolute pressure measurements, the sensor itself must be physically separated and enclosed in a hermetic chamber, which is pressurized during measurement. Current atmospheric pressure needs to be subtracted in software from the tire pressure indicated by the sensor to display correct differential tire pressure.
Mechanical construction of the first prototype is shown under figure.
The sensor, with its power supply decoupling capacitor, is placed on a separate PCB. Connection between the main board and the sensor PCB is achieved by a miniature connector pair. This enables easy sensor PCB extraction and replacement in the prototype system. The main PCB is secured in the enclosure by a single M3 screw, while the
sensor PCB is held in position only by the connector friction.
Prototype PCBs
Actual width of the main PCB is approximately 38mm
A photograph of the assembled gauge is shown under :
