What is grounding?

Grounding is one of primary ways to minimize unwanted noise and pickup.

There are two basic objectives involved in designing good grounding systems.

i) To minimize noise voltage generated by currents from two or more circuits flowing thorugh a common ground impedance.

ii) To avoid creating ground loops which are susceptible to magnetic fields and differences in ground potential.

Grounding, if done improperly however, can become a primary means of noise coupling.

In most general sense a ground can be defined as equipotential point or plane which serves as a reference voltage for a circuit or system. By equipotential point we mean the point where voltage does not change regardless of the amount of current supplied to it or drawn from it. 

If the ground is connected to earth through a low impedance path, it can then be called an earth ground.

There are two common reasons for grounding a circuit:

i) For safety

ii) To provide an equipotential reference for signal voltages

Safety grounds are always at earth potential where as signal grounds are usually but not necessarily at earth potential.

In many cases, a safety ground is required at a point which is unsuitable for a signal ground, and this may complicate noise problem. 

  

Discovery of X-rays

Wilhelm Roentgen was professor of physics at university of Wurzburg, Germany when he discovered X-rays in 1985. The discovery was entirely serendipitous; Roentgen was merely studying a beam of electrons in a highly evacuated glass vessel. When the electrons, moving at great speed slammed into glass wall, they produced a very high penetrating radiation - a wholly unexpected occurrence. Roentgen first noticed the radiation when it caused a paper coated with Barium Platino-cyanide to glow. The chemical compound was a standard detector of UV light which causes the chemical to fluorescence i.e. to emit visible light after it has absorbed UV light. But Roentgen's evacuated vessel was tightly covered with black cardboard and so no UV light could emerge from it. The glow must be some other kind of radiation.

When he announced the discovery of the new radiation, Roentgen wrote:

"I posesss, for instance, photographs of ............the shadow of bones of hand, the shadow of a covered wire enclosed in a box.........."

Earlier in the paper, he noted that "the darker shadow of bones is seen with in the slightly dark shadow image of hand itself.

The new radiation quickly became a diagnostic tool in hospitals all over the world. Roentgen could not determine what the rays are made of and thus rays are named as X-rays.