Switch

In electrical engineering, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. The mechanism of a switch may be operated directly by a human operator to control a circuit (for example, a light switch or a keyboard button), may be operated by a moving object such as a door-operated switch, or may be operated by some sensing element for pressure, temperature or flow. A relay is a switch that is operated by electricity. Switches are made to handle a wide range of voltages and currents; very large switches may be used to isolate high-voltage circuits in electrical substations.

Description

The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is nonconducting. The mechanism actuating the transition between these two states (open or closed) can be either a "toggle" (flip switch for continuous "on" or "off") or "momentary" (push-for "on" or push-for "off") type.

TCO Certification

TCO Certification is a series of product certifications for office equipment based on user friendliness, safety, and products’ eco-friendliness. It is administered by TCO Development, owned by the Swedish Confederation of Professional Employees, TCO (Tjänstemännens Centralorganisation). Although commonly associated with computer monitors, later TCO revisions also define standards for computers, keyboards, printers, mobile phones, and office furniture. It is the precursor of TCO Certified.

TCO'92

The first TCO certification, for 1992, defined low emission standard for computer displays, and power management features, which is a superset of MPR-II standards.

TCO'95

TCO'95 expands certification category to CRT displays, keyboards, system units. Within each item, the standard addresses ergonomics, emissions, energy, and ecology involved into making the certified product.

Ergonomics

Arterial blood gas

An arterial blood gas (ABG) test is a blood gas test of blood from an artery; it is thus a blood test that measures the amounts of certain gases (such as oxygen and carbon dioxide) dissolved in arterial blood. An ABG test involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or other sites are used. The blood can also be drawn from an arterial catheter. An ABG test measures the blood gas tension values of arterial oxygen tension (PaO₂), arterial carbon dioxide tension (PaCO₂), and acidity (pH). In addition, arterial oxygen saturation (SaO₂) can be determined. Such information is vital when caring for patients with critical illness or respiratory disease. Therefore, the ABG test is one of the most common tests performed on patients in intensive care units (ICUs). In other levels of care, pulse oximetry plus transcutaneous carbon dioxide measurement is an alternative method of obtaining similar information less invasively.