Notes, abstracts, papers, exams and problems of Technology

Silicon Controlled Rectifiers (SCRs)

Introduction

SCRs are unidirectional devices, meaning they conduct current in only one direction, unlike TRIACs, which are bidirectional. SCRs are typically triggered by current flowing into the gate, whereas TRIACs can be triggered by either positive or negative current applied to their gate.

Construction

SCRs comprise four semiconductor layers, forming NPNP or PNPN structures with three P-N junctions (J1, J2, J3) and three terminals: anode, cathode, and gate. The anode connects to the p-type material, the cathode to the n-type layer, and the gate to the p-type material nearest the cathode.

These layers alternate between p- and n-type silicon with added dopants. Junctions are formed through diffusion or alloying.... Continue reading "Understanding Silicon Controlled Rectifiers (SCRs)" »

Ferrous Metals

Iron minerals from the Earth's surface undergo different processes to obtain pure iron and its alloys: steel and cast iron.

Percentage of Carbon:

• Pure Iron: The concentration of carbon is between 0.008% and 0.03%.
• Steel: Between 0.03% and 1.76%.
• Cast Iron: Between 1.76% and 6.67%.

Pure Iron

Advantages: Good magnetic properties. Disadvantages: Melts only at high temperatures; difficult to machine. Uses: Electronics and electrical components.

Cast Iron

Properties: Very hard and resistant. Uses: Machine parts, lamps, pistons, drain covers.

Steel

Properties: Very hard and resistant; easy to weld. Uses: Construction, boats, tools, screws, domestic appliances, etc.

Metallurgy

Iron metal is washed to eliminate any impurities. It is crushed and sieved... Continue reading "Ferrous and Non-Ferrous Metals: Properties & Uses" »

The Importance of Drawing in Civil Engineering

Drawing is a fundamental and very important subject in Civil Engineering. A civil engineer cannot be successful without knowing how to draw. It is the language of engineers. No amount of words can convey civil engineering information as accurately and efficiently as a drawing. An architect cannot describe the plan of a house to a builder unless they draw it. They can only give a general idea using words like "single-storied, three-bedroom house," etc., but without a drawing, there is no way to build the house. This language is the easiest in the world to learn and the most precise. An object can be drawn only in one way. As a corollary, an accurate and complete drawing of an object can represent... Continue reading "Essential Drawing Tools and Techniques in Civil Engineering" »

Unijunction Transistor (UJT)

A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch. The UJT is not used as a linear amplifier. It is used in free-running oscillators, synchronized or triggered oscillators, and pulse generation circuits at low to moderate frequencies (hundreds of kilohertz). It is widely used in the triggering circuits for silicon controlled rectifiers. The low cost per unit, combined with its unique characteristic, have warranted its use in a wide variety of applications like oscillators, pulse generators, saw-tooth generators, triggering circuits, phase control, timing circuits, and voltage- or current-regulated supplies.... Continue reading "Unijunction Transistor (UJT): Construction, Operation, and Applications" »

What Does a Flashing Yellow Light Mean?

1) Proceed with caution.

At Night, It's Hard to See:

1) Pedestrians.

If the Rear of Your Vehicle Starts to Skid Left, You Should:

1) Steer left.

Two Cars Come to an Intersection at the Same Time. Which of the Following is True?

1) The car 'A' turning left must yield.

Before You Leave a Parking Space, Which is Parallel to the Curb, You Should:

1) Look for traffic by turning your head.

When Two Vehicles Enter an Intersection from Different Highways at the Same Time, Which Vehicle Must Yield the Right of Way?

1) Vehicle on the left.

What Should You Do When You Are Going to Enter a Roadway from a Private Road?

1) Yield the right of way to pedestrians and roadway traffic.

The Driver's Left Hand and Arm are Extended Upward.

Machining and CNC

15—Free—Tied Up---By—should---Take—Thursday—Make—Say—Then—confirm—short—On—until

16---Logistics manager—Outsource---Inventories---Competitive market---Trends---Product cycle times

17—Match these phrases diagram 1B—2E—3G—4I—5D—6A---7C—8F—9H—10J

18---Comparative Adverb---Prints faster---Runs better---Cuts worse---Get up earlier---Drives more carefully---Finished later---Work harder

19-- have—repaired---was—Isoldered—ordered—called-- haven´t had

20—Predictions---Resist---Store---Replace---Perform---Take---Send---Remove---Clean up---Wear---Stop

Possibilities 2-Steel springs. He wants them made in plastic

Exercise 4- (1 d) (2a) (3c) (4b) (5e)

21---True—False---True---False---False-... Continue reading "Machining and CNC: Processes, Techniques, and Applications" »

Topic 1. Test

• Test=prueba
• Broad=amplia
• Assess=evaluar
• Manufacture=fabricar
• Power transmission=transmisión de potencia
• Improve=mejorar

E1: Hi, I’m Ian Moore. I’m here for an interview.

E2: It’s nice to meet you, Ian. Tell me about your work experience.

E1: Well, I worked for Escribano for twelve years.

E2: What were your job duties?

E1: I assessed old engine models. Then I made suggestions to improve them.

E2: Did you design any engines?

E1: Not on my own. I designed new parts for older models.

E2: If we hire you, you’ll design new ones as well.

Topic 2. Bearings / Cojinetes

• Ball bearing=rodamiento de bolas
• Thrust roller bearing=rodamiento de rodillos de empuje
• Tapered roller bearing=rodamiento de rodillos cónicos
• Straight roller bearing=rodamiento de

Cloud Computing: An Overview

Cloud computing allows access to data and software over the internet, eliminating reliance on hard drives or SSDs. This facilitates convenient online backups of photos and private data, mitigating concerns about hardware crashes or viruses.

Cloud Provisioning

Cloud service providers invest heavily in storage hardware, data centers, and their maintenance, addressing temperature, security, humidity, hardware obsolescence, and more. Cloud provisioning encompasses various methods:

• Advance Provisioning: Clients contact providers, resources are prepared in advance, and fees are charged annually or monthly.
• Dynamic Provisioning: Resources are assigned as needed, often on a pay-per-use basis.
• User Self-Provisioning: Users purchase

Functions of the Drillstring:

• Transmits rotation to the drillbit
• Exerts weight on the bit; the compressive force necessary to break the rock
• Guides and controls the trajectory of the bit
• Allows fluid circulation for cooling and cleaning

Components of the Drillstring:

• Drillpipe
• Drillcollars
• Accessories including:

• Heavy-walled drillpipe (HWDP)
• Stabilisers
• Reamers
• Directional control equipment

The Kelly:

• Transmits rotation and weight-on-bit to the drillbit
• Supports the weight of the drillstring
• Connects the swivel to the uppermost length of drillpipe
• Transmits drilling fluid from the swivel into the drill string

The Top Drive:

A combined rotary table and Kelly mounted on the rig's swivel, assisting in pipe handling during operations.

Drilling Problems:

• Pipe Sticking
• Lost