The computer

Types of welding techniques
Before you chose a welding machine, you must know which kind of welding technique you will apply. Each welding techniques requires a specific type of welder.
Stick Welding/SMAW
Stick welding uses an electric current flowing from a gap between metal and welding stick (arc welding electrode).

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  works with most alloys or joints
  
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  can be used indoors and outdoors, and in drafty areas
  
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  works with rusty and dirty metals
  
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  good for thicker metals
  
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  economical
  

pressure
Pressure, in the physical sciences, the perpendicular force per unit area, or the stress at a point within a confined fluid. The pressure exerted on a floor by a 42-pound box the bottom of which has an area of 84 square inches is equal to the force divided by the area over which it is exerted; i.e., it is one-half pound per square inch. The weight of the atmosphere pushing down on each unit area of Earth’s surface constitutes atmospheric pressure, which at sea level is about 15 pounds per square inch. In SI units, pressure is measured in pascals; one pascal equals one newton per square metre. Atmospheric pressure is close to 100,000 pascals.
The pressure exerted by a confined gas results from the average effect of the forces produced on the container walls by the rapid and continual bombardment of the huge number of gas molecules. Absolute pressure of a gas or liquid is the total pressure it exerts, including the effect of atmospheric pressure. An absolute pressure of zero corresponds to empty space or a complete vacuum. Measurement of pressures by ordinary gauges on Earth, such as a tire-pressure gauge, expresses pressure in excess of atmospheric. Thus, a tire gauge may indicate a pressure of 30 pounds (per square inch), the gauge pressure. The absolute pressure exerted by the air within the tire, including atmospheric pressure, is 45 pounds per square inch. Pressures less than atmospheric are negative gauge pressures that correspond to partial vacuums

Capacitive pressure measure device

These sensors are the most reliable and have been used on million of applications. They are based on transducers whose pressure applied to diaphragm sensors produces a variation of capacitance between them and a central diaphragm, for instance. This variation is typically used to vary an oscillator frequency, used as a capacitor bridge element and also to vary an oscillator frequency. This frequency can be measured directly by the CPU and converted into Pressure. In this case there is no A/D conversion and contributes to the exactness and elimination of drifts encountered on analog/digital conversions. It is worth remembering that this reading principle is totally digital and is used by Smar since the middle 80s. Smar is the only Brazilian company and one of the few in the world to make this type of sensor. They have linear and practically insensitive to temperature variations, being the favorite for instrumentation and process control, as they have excellent performance on stability, temperature and static pressure. Some of their best features:

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  Ideal for low and high pressure applications.
  
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  Minimize the Probable Total Error and consequently process variability.
  
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  Ideal for flow applications.
  
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  Their lineal response allows high rangeability exactness
  

Temperature
Temperature is the measure of hotness or coldness expressed in terms of any of several scales, including Fahrenheit and Celsius. Temperature indicates the direction in which heat energy will spontaneously flow—i.e., from a hotter body (one at a higher temperature) to a colder body (one at a lower temperature). On average, the time of day when air temperature is the highest is usually about 3 PM, as heat continues to build up after noon. However, after 3 PM the Sun is low enough in the sky for more heat to be lost than absorbed, causing a gradual decline in air temperature. During the night there is no direct sunlight, so there is more solar energy being lost than absorbed, causing air temperature during the night to be relatively cooler than during the day. Temperature decreases at higher altitudes because there is less air exerting pressure than at sea level. According to Gay-Lussac’s law, pressure and temperature at a constant volume are directly proportional, so if there is a decrease in pressure, temperature will consequently decrease. Temperature inversions occur when the normal heat gradient of the atmosphere—air is warmer near the ground and cooler in the sky—is reversed. A temperature inversion typically occurs in the late evening and disappears just after sunrise. A visual cue that a temperature inversion has happened is fog (or smog in an urban environment).