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Specifications












Guidelines : Specifications

Specifications

Guidelines

  • (Note: Because specifications vary so widely from subject to subject, all of the following guidelines won’t apply in every case.)
  • Take care with assumptions about your readers’ knowledge. Almost always with specifications, you will be writing for more than one reader. Know their background, knowledge, and recent familiarity with your subject. When in doubt, explain.
  • Overview the objectives of a process, project, or equipment before beginning specific details.
  • Try to pinpoint and briefly state the number of stages, steps, or components in the process, instruction, or description. Such breakdowns make the entire subject more understandable.
  • In describing equipment, begin with the internal parts and move to the outer or vice versa, whichever arrangement seems more logical. However, don’t move back and forth between the two detail arrangements.
  • Define unfamiliar terms the first time you use them. How do you know in a technical field which terms are unfamiliar? Again, knowing your audience is essential. In general, it’s always better to give an “unnecessary” definition than to omit a necessary one.
  • Use abbreviations to cut word length, but make sure they are standard and well known.
  • Mention prominently any safety precautions and repeat again before the step or section in which the precaution should be taken.
  • Give steps in chronological order. Indicate each step in a separate sentence. Otherwise, the steps may be understood as simultaneous rather than separate, sequential actions.
  • Write instructions in the imperative mood: “Monitor these compasses for …” rather than “These compasses should be monitored for …”; “Cover the abutting end surfaces with an approved sealing material” rather than “The abutting end surfaces shall be covered with an approved sealing material.”
  • Make text and drawings complement, rather than duplicate, each other. For instance, you may tell in text how a tube clamps onto a reduction fitting and give the tube dimensions in a drawing. The problem in repeating information in two places is twofold: 1) Either the drawing or the text may be changed at some later date without accompanying changes in the other document, thus resulting in contradictory details; 2) The same information may be re-worded for “clarification,” thus resulting in two separate interpretations. If you need to repeat information in two places, make sure your wording is an exact repetition.
  • Place supporting tables, sketches, charts, photographs, or lists as close to their mention in the text as possible.
  • Use numerals instead of written numbers.
  • Give kinds, classes, or grades of materials in a manner that permits you to be specific for all situations. To do this, begin with the exceptions and then lump into “all the rest” categories. For example: Pipe: 3/8 inch for lavatories and water fountains; 1/2 inch for all sprinkler systems; 3/4 inch for all other water lines.
  • Break up long blocks of text. Use frequent section or paragraph titles; use lists; or put key words or phrases in capital letters, italicize them, or underline them. These aids allow your reader to skim as with a reference manual or legal document without reading large blocks of text. Highlight significant details by placing them alone in a separate, short paragraph.
  • Don’t include a “Scope of Work” section. Its usual vagueness makes it meaningless and dangerous. Like other introductions, “Scope of Work” sections tend to be padding that says simply, “Later I’m going to tell you something important and specific.” These sections can be dangerous: Readers may glance at the section thinking they have the whole picture and later find “minor” surprises surfacing in the detailed sections. When “Scope of Work” sections are at their best–specific–they become redundant.
  • Don’t use all-encompassing catch clauses such as the following: “The company shall complete and include everything for full operation of the system with all work subject to approval by our engineers.” Open to many interpretations, such comments usually mean, “Guess what may turn up later that I want you to do.”
  • Don’t add “etc.” at the end of a list. This suggests the writer doesn’t know what the list consists of or is too lazy to finish the writing. The “etc.” only raises questions.

Example 1: Sample of specification letter

Memorandum

TO:

FROM:

DATE:

SUBJECT: Description of the Spectrograph (Monochromator) Body

The spectrograph is an optical instrument used to perform qualitative or semiquantitative chemical analyses based on intensities of spectral lines emitted by excited atoms.

The body of the spectrograph consists of a large brass cylinder, 48 inches long, 16-1/2 inches outside diameter, and 1/4 inch wall thickness. This cylinder is closed at each end and has provision for attaching a diffusion pump and a vacuum gauge (an ionization gauge).

The two END PLATES on the cylinder and the two 1-5/8-inch-wide FLANGES, 19 inches in diameter, are made of 1/4-inch-thick Muntz metal. Muntz metal is an alloy consisting of 60 percent copper and 40 percent zinc.

Each FLANGE contains a 1/4-inch-deep groove so it can be fit snugly over the ends of the cylindrical body. On the opposite side of each flange is a groove, 0.206 x 0.003 inch wide. A Parker O-ring seal, size 2-461, 16 inch inside diameter, 1/4 inch thickness, made of butyl rubber base (material number E 515-8), can be placed into the groove for proper vacuum sealing with the end plate.

Each flange and end plate has 12 equally spaced 1/4 inch holes drilled through it. These holes are centered on an 18-1/2-inch-diameter bolt circle. Each flange is secured to the cylindrical body with tin-lead solder.

The end plates are held in alignment with the flanges by means of two large steel HINGES. These hinges enable one person to open the spectrograph and swing the end plates out of the work area without strain. Each hinge is fastened to the back side of an end flange with four 1/4-inch-diameter, 1-1/4-inch-long bolts.

When an O-ring has been seated in the groove of a flange, the end plate swings into position so its machined surface is flat against the O-ring. The 12 bolts can then be tightened to a torque of 8-1/2 foot-pounds so the O-ring is compressed into the groove by the end plate, thus making a vacuum-tight seal.

Two pieces of 1/4-inch-thick aluminum, alloy 2024-T351, are used to provide a SHELF. The aluminum pieces are held together, side by side, by three cleats on the underside. The shelf is 15 inches wide and therefore rests below the center of the cylindrical cross section of the body. The shelf’s length is 42-1/2 inches. This length allows 1 inch of space between the end of the shelf and the front-end plate and 4 inches’ space at the rear end. Thus, pumping speed is not retarded by the presence of the shelf.

Example 2: Product specification letter

Memorandum

TO:

FROM:

DATE:

SUBJECT: Specifications for Pile Hammer

1. Pile hammers used to install cylinder piles shall be capable of developing a rated energy per blow of no less than 122,000 joules (90,000 foot-pounds). The hammer shall have a minimum ram weight of 27,215 kilograms (65,000 pounds) and an adjustable stroke.

2. The hammer shall be equipped with a capblock composed of alternating layers of aluminum and Micarta plates. The layers will cushion the blow of the ram on the follower.

3. Followers shall cover the entire head of the cylinder pile, maintaining concentricity between the hammer and pile, efficiently transmitting blow energy from hammer to pile, and enclosing an acceptable wood cushion to protect the head of the pile during driving.

4. A wood cushion block at least 152mm (6 inches) thick shall be used on the head of the pile to distribute the hammer-to-blow energy uniformly. The cushion block shall be composed of layers of 19mm-thick plywood or an acceptable alternate as approved by the designer. The dimension shall be such as to cover completely the concrete cross section of the pile.

Example 3: Specification product letter

Memorandum

TO:

FROM:

DATE:

SUBJECT: Specifications for Computer Housings

The computer housings shall be made of 5 mm. thick metal able to withstand 40 lbs. of pressure at any point. The measurements on the outside shall be 6” high, 18” wide, and 20” deep.

A 1.5” x 5” hole in the housing to accommodate a disk drive shall be on the upper right corner of the front face, .5” from the top edge and 2” from the right side edge.

A 1.5” x 6” hole in the housing to accommodate a CD-ROM drive shall be on the lower right corner of the front face, .5” from the bottom edge and 2” from the right side.

Four circular holes 1” in diameter shall be located on the front face. The first hole shall be placed 1” from the left edge and 1” from the bottom edge. Each of the other three holes shall be 1” to the right of the previous one.

Example 4: Example letter of specifications

Memorandum

TO:

FROM:

DATE:

SUBJECT: Green Fuel Pump Nozzle–Specifications

The green fuel pump nozzle is designed to meet E.P.A. specifications under the 1998 Fresh Air Act. The nozzle is defined as the handle and metal piping which attach to the hose running from an unleaded fuel pump.

The green nozzle is the same shape and material as standard fuel nozzles:

1. A 16 inch long aluminum pipe measures 1.25 inches in diameter on the outside and 1.05 inches in diameter on the inside. The 6.5 inches of pipe which run across the top of the handle are straight. The 9.5 inches which are inserted into the fuel tank are curved 15 degrees.

2. Two inches of the pipe are fitted into a rectangular aluminum handle measuring 6.5 inches long by 4 inches tall on the outside. The handle is also .5 inches thick and 1 inch wide. Grooves .2 inches high border the inside edge of the 4 inch tall sides

3. Fitted into the grooves, running lengthwise inside the handle is a trigger. The trigger is a 6 inch long by 1 inch wide by .2 inches thick aluminum bar. The valve on the hose which regulates fuel flow has a clamp which attaches to the trigger, allowing trigger movement to operate the valve.

The green fuel nozzle differs from the standard nozzle in the following ways:

4. A circular rubber splash and fume guard sits at the point were the pipe meets the handle. The guard is 5 inches in diameter and .25 inches thick. A circular hole 1.25 inches in diameter located in the center of the guard allows the guard to be fitted onto the pipe.

5. Rubber .2 inches thick coats the entire handle and trigger.

6. A 5 inch long tube of .2 inch thick rubber with 5 accordion folds is fitted onto the pipe beginning at the splash and fume guard and ending 4.5 inches before the curved opening of the pipe.

Example 5: Product detail letters

Memorandum

TO:

FROM:

DATE:

SUBJECT: Specifications for a Bindery Cutting Machine

The cutting machine is capable of cutting 2000 sheets of paper per minute. Blades adjust to cut any size from 4” by 4” to 2’ by 2’. The automatic paper loader has a 1,000,000 sheet capacity.

Four 2’ long steel blades are mounted over the 4’ by 4’ cutting bed. .25 inch thick clear plastic guards, 2’ long by 1.5’ tall encase the blades.

A hydraulic pump is capable of lowering the blades with 110,000 foot-pounds of force.

The control console, located 2’ from the cutting bed, contains blade and paper loader speed controls and hydraulic pump force controls.

The console-area also contains three safety features. A 3’ high and .5” thick shatterproof glass shield separates the control console from the cutting bed. A two-button engage mechanism on the console ensures technician’s hands are away from moving parts while the cutter is in operation. An emergency shut-off switch automatically raises blades and turns off the machine.

Example 6: Specifications of product

Memorandum

TO:

FROM:

DATE:

SUBJECT: Specifications–Plastic Injection Mold

The plastic injection mold is a two-half, solid stainless steel mold used in plastic injection machines. The machines force molten plastic into the mold’s center reservoir, where it cools and hardens into the mold shape to make a plastic part.

The 2 halves of the mold must be 2 feet high by 2.5 feet wide by 1.5 feet deep. The center reservoir sides of each half must be flush around the reservoir when they come together.

The back side of each half, the side opposite the reservoir, is installed into the injection machine. 6 pins, each 6 inches long and 1 inch in diameter, protrude perpendicular to the back side. Four pins are located 1 inch from each corner. The other 2 pins are located in the center of the back side: one being 1 inch from the top edge and the other being 1 inch from the bottom edge.

A 1.5 inch tall by .5 inch wide hole runs from the center reservoir to the back side in the center of the mold. This hole accommodates the injection tube and a water hose to regulate mold temperature.

Example 7: Specifications for service

Memorandum

TO:

FROM:

DATE:

SUBJECT: Specifications for a Clipboard Style Mini-Computer

The clipboard style mini-computer is a record keeping device for National Parcel Delivery drivers.

The mini-computer is 11” x 8.5” x .5” and weighs under 4 lbs. It is able to withstand an impact of 100 foot-pounds.

A 1” x 6” 5000 pixel LCD screen displays entries from an alphabetic and numeric touch pad. A pen bar code reader fits into a plastic holder on the top of the mini-computer.

One record consists of a package’s bar code and recipient’s first and last names. The mini-computer has at least a 2,000 record storage capacity. It can access records either by name or bar code.

The mini-computer has download and upload ports on the top edge. Each port is covered by a removable rubber plug which protects the port from dust.

Example 8: Specifications of machine

Memorandum

TO:

FROM:

DATE:

SUBJECT: Ceramic Kiln–Specifications

1. The kiln used to fire clay shall be no more than 5 feet tall, 5 feet wide, and 3 feet deep on the outside. The outside of the kiln shall not exceed 80 degrees Fahrenheit regardless of the temperature inside the kiln.

2. The door of the kiln shall have a window of 1 inch thick insulated glass. The door handle cannot exceed 80 degrees Fahrenheit regardless of the temperature inside the kiln.

3. Two removable shelves shall be inside the kiln, each accommodating clay structures of up to 2 feet high and 350 pounds. Each shelf withstands at least 1000 degrees Fahrenheit.

4. The kiln shall be able to heat to 900 degrees Fahrenheit within 1 hour. A thermostat shall control temperature. There shall be no more than 10 degrees Fahrenheit difference between the heat in any two areas of the kiln at any time.

5. The control panel shall include temperature set dials, an automatic shut-off timer dial, and an emergency shut-off switch.

Example 9: Specifications memos

Memorandum

TO:

FROM:

DATE:

SUBJECT: Truck Scale Specifications

The truck scale is an instrument which weighs semi and other large trucks to determine if they comply with state weight requirements.

Trucks drive onto the scale platform, a 15’ x 50’ cement platform that sits flush with the ground. A truck’s front axle should be directly over the white line in order to obtain a proper measurement.

The scale is able to weigh up to 500 tons. It is adjusted monthly to within 10 lbs. accuracy.

Every 10 feet a weight register makes a separate measurement of the weight at that location on the truck. This feature indicates whether a truck’s load is even. The measurements taken every 10 feet and the total weight of a truck register on the electronic monitor in the inspection building.

Example 10: Specifications

Memorandum

TO:

FROM:

DATE:

SUBJECT: Specifications for a Self-Service Credit Card Reader

The self-service credit card reader is a customer-friendly magnetic strip reader compatible with the four major credit card companies’ electronic authorization systems.

The 4 inch by 5 inch by one inch card reader is mounted in the grocer store check-out aisle with the keypad and magnetic strip reader facing the customer.

Adjacent to the magnetic strip reader is a picture depicting the correct way to position the card in the reader.

The keypad includes numbers 0 through 9, a green key reading “Yes/Enter,” and a red key reading with “Erase/Cancel.”

     

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