NTS STUDY

IS 1491:1959 prismatic compass ke liye sabse purana aur mazboot standard hai jo aaj bhi survey labs aur field works mein follow kiya jata hai. Ye code 1959 mein banaya gaya tha aur instruments ki manufacturing quality ko control karta hai.

Is code ki poori detail technical point-of-view se niche di gayi hai:

IS 1491:1959 – Specification for Prismatic Compass

1. Scope (Kiske liye hai?)

Ye standard 85 mm, 100 mm aur 110 mm nominal size wale prismatic compass ke liye specifications deta hai. Ismein Liquid type (A) aur Dry type (B) dono shamil hain.

2. Construction & Design (Banawat)

• Non-Magnetic Body: Compass ki body aisi metals (Aluminium ya Brass) se banni honi chahiye jo magnetic needle ko disturb na karein.

• Prism: Prism high-quality optical glass ka hona chahiye jiske upar ek "Sun-shade" (Dark glasses) laga ho taaki dhoop mein bhi reading dikhe.

• Pivot: Pivot hamesha "Hardened Steel" ya "Iridium" ka hona chahiye taaki needle bina ruke smoothly ghum sake.

3. Graduated Ring (Graduation)

• Anti-Clockwise Marking: IS 1491 ke mutabiq, prismatic compass mein readings hamesha South se shuru ($0^\circ$) hoti hain aur clockwise direction mein badhti hain (West $90^\circ$, North $180^\circ$, East $270^\circ$).

• Inverted Figures: Ring par numbers ulte (Inverted) likhe hote hain taaki prism se dekhne par wo humein seedhe aur saaf dikhein.

4. Accuracy & Sensitivity

• Least Count: Is code ke mutabiq compass itna accurate hona chahiye ki hum 30 minutes ($30'$) tak ki reading bina kisi confusion ke le sakein.

• Error Limits: Needle hamesha Magnetic North se align honi chahiye. Agar error $30'$ se zyada hai, toh wo instrument IS standard ke mutabiq fail mana jata hai.

5. Liquid vs Non-Liquid (Type A vs Type B)

• Type A (Liquid): Ismein "Alcohol" aur "Water" ka mix ya "Purified Kerosene" bhara hota hai. Ye needle ke vibrations ko turant rok deta hai (Damping), jisse reading jaldi milti hai.

• Type B (Dry): Ismein koi liquid nahi hota. Needle ko haath se ya "Brake Pin" se rokna padta hai.

6. Major Components as per IS 1491

1. Lifting Pin: Jab hum compass band karte hain, toh lifting pin needle ko pivot se upar utha deti hai taaki pivot ghisne se bach jaye.

2. Agate Cap: Needle ke niche ek pathar (Agate) laga hota hai jo frictionless movement deta hai.

3. Vanes: Sighting vane mein "Horsehair" (ya fine wire) hona chahiye taaki object ko accurately bisect kiya ja sake.

NTS Study (Nodal Theory) Pro Tip:

Site engineers ke liye ye code isliye zaroori hai kyunki agar aapka compass IS 1491:1959 ke mutabiq hai, toh iska matlab hai ki uski Agate Cap aur Pivot itne majboot hain ki wo kayi saalo tak accurate reading denge.

Surveying Interview Question: "Prismatic compass mein zero ($0^\circ$) South par kyu hota hai?"

Answer: Kyunki prism hamesha observer ki side (South) hota hai aur reading uske niche se dekhi jati hai, isliye alignment ke liye zero South par rakha jata hai (IS 1491 standard).