science

Penetron

Penetron is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Penetron rather than just read about it. In short: The penetron, short for penetration tube, is a type of limited-color television used in some military applications. Unlike a conventional color television, the penetron produces a limited color gamut, typically two colors and their combination.

Key takeaways

Penetron belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Penetron to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Penetron from memory before moving on to harder problems.

Reference excerpt

The penetron, short for penetration tube, is a type of limited-color television used in some military applications. Unlike a conventional color television, the penetron produces a limited color gamut, typically two colors and their combination. Penetrons, and other military-only cathode-ray tubes (CRTs), have been replaced by LCDs in modern designs.

History

Basic television A conventional black and white television (B&W) uses a tube that is uniformly coated with a phosphor on the inside face. When excited by high-speed electrons, the phosphor gives off light, typically white but other colors are also used in certain circumstances. An electron gun at the back of the tube provides a beam of high-speed electrons, and a set of electromagnets arranged near the gun allow the beam to be moved about the display. The television signal is sent as a series of stripes, each one of which is displayed as a separate line on the display. The strength of the signal increases or decreases the current in the beam, producing bright or dark points on the display as the beam sweeps across the tube. In a color display, the uniform coating of white phosphor is replaced by dots or lines of three colored phosphors, producing red, green or blue light (RGB) when excited. These primary colors mix in the human eye to produce a single apparent color. This presents a problem for conventional electron guns, which cannot be focused or positioned accurately enough to hit these much smaller individual patterns. A number of companies were working on various solutions to this problem in the late 1940s, using three separate tubes or a single white-output with colored filters placed in front of it. None of these proved practical and this was a field of considerable development interest.

Penetron The penetron was original designed by Koller and Williams while working at General Electric (GE). It was initially developed as a novel way to build a single-gun color television with the simplicity of a conventional B&W set. Like the B&W tube, it used a uniform coating of phosphor on the display with a single electron gun at the rear. However, the phosphor coating is applied in three layers of different colors, red on the inside closest to the gun, then green, and blue on the outside closest to the front face of the tube. Colors were selected by increasing the power of the electron beam, which allowed the electrons to flow through any lower layers to reach the proper color. In a conventional set, voltage is used to control the brightness of the image, not its color, something that the new design also had to achieve. In the penetron, voltage is also used to select the color. To address these competing needs, the color selection was provided by an external mechanism. The gun was modulated by voltage as it would be in a B&W set, with increasing power producing a brighter spot on the screen. A set of fine wires placed behind the screen then provided extra energy needed to select a particular color layer. Since the phosphors were relatively opaque, the system required very high accelerating voltages, between 25 and 40 kV. An improved version was introduced that used transparent phosphor layers and thin insulating layers between them that reduced the required voltages. The dielectric ensured that stray electrons, either off-voltage from the guns or secondary emission from the phosphors themselves, were stopped before they reached the screen. The penetron was ideally suited for use with the early CBS broadcast system, which sent color information as three separate sequential frames. CBS' experimental televisions used a mechanical filter with three color sections that spun in front of a B&W tube. The same timing signal was used in the penetron to change the voltage of the color selection grid, to the same end. The low switching rate, 144 times a second, meant that the changing high-voltage was not a major source of high-frequency noise. Unlike the mechanical CBS system, the penetron had no moving parts, could be built at any size (which was difficult to do with the disk), and had no problems with flicker. It represented a major advance in display technology.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Penetron

Start with the simplest possible case. Write down what Penetron claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Penetron before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Penetron ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Penetron

In research: Penetron appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Penetron in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Penetron is common in secondary-school and first-year university syllabi. It links to neighbouring topics Early color television, Television technology, Vacuum tube displays, so understanding it makes those chapters shorter.
In everyday life: Look for Penetron outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Penetron in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Penetron means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Penetron out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Penetron in simple terms?

Why does Penetron matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Penetron?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Penetron.