IOCL Junior Operator Solved Questions & Answers || IOCL Junior Operator General Science Questions and Answers

• The most common way to calibrate portable instruments is by comparing their readings against a more accurate, high-grade standard instrument.
• This ensures the portable instrument provides readings that are close to the known accurate values.

High precision digital instruments are better than analog instruments for calibrating because they are more accurate, have higher resolution, are less affected by the environment, are easier to use, and are more stable.

PMMC (Permanent Magnet Moving Coil) instruments have all the listed advantages:

• They have a uniform scale: PMMC instruments have a uniformly divided scale because the instrument’s response is directly proportional to the deflection of the pointer. The scale may be very long, over about 250 or 270 degrees.
• They consume less power: PMMC instruments consume low power.
• They have efficient damping: PMMC instruments have efficient damping characteristics and are not affected by stray magnetic fields. The damping torque is generated by the motion of the aluminum coil former within the magnetic field, reducing unwanted oscillations in the pointer

PMMC (Permanent Magnet Moving Coil) instruments, while offering several advantages, also have some limitations:

• Cost: PMMC instruments are generally more expensive to manufacture compared to moving iron instruments due to the use of permanent magnets and precision components.

• DC Measurements Only: PMMC instruments can only be used for measuring DC (Direct Current). They cannot be directly used for measuring AC (Alternating Current) because the direction of the current reverses periodically, causing the pointer to oscillate rapidly.

• Error Due to Loss of Magnetism: The permanent magnet used in PMMC instruments can lose its magnetism over time due to aging, demagnetization, or exposure to strong magnetic fields. This loss of magnetism can lead to measurement errors.

• Moving iron instruments work because of magnetic force.
• When current flows through a coil, it creates a magnetic field that attracts a piece of iron, causing it to move and indicate a reading on the scale.

• The moving part of a moving iron instrument is made of soft iron.
• This material is easily magnetized and demagnetized, allowing it to respond quickly and accurately to changes in the magnetic field produced by the instrument’s coil.

There are two main types of moving iron instruments:

• Attraction Type: In this type, a single piece of soft iron is pulled towards the coil when current flows through it.
• Repulsion Type: In this type, two pieces of soft iron are placed inside the coil. When current passes, both pieces become magnetized and repel each other, causing the movement of the moving piece.

In attraction-type moving iron instruments, the soft iron piece is typically oval-shaped for several important reasons:

• Effective Magnetic Field Interaction: The oval shape allows the soft iron piece to interact more effectively with the magnetic field produced by the coil. This design helps to evenly distribute the magnetic field, which maximizes the attractive force.
• Precise Deflection: The oval shape enables the soft iron piece to rotate in a specific and predictable direction, providing precise deflection that is crucial for accurate measurements.
• Controlled Movement: Thanks to its oval shape, the soft iron piece can rotate smoothly and in a controlled manner, enhancing the instrument’s sensitivity and accuracy. Reduction of Non-
• Linear Scale: The oval shape contributes to a more uniform response to changes in the magnetic field, helping to minimize the problem of a non-linear scale.

• The soft iron piece in an attraction-type moving iron instrument is pivoted eccentrically (off-center).
• This allows the iron to be pulled into the coil’s magnetic field, creating the movement needed for measurement.

• The function of jeweled bearings in a moving iron instrument is to allow free movement of the spindle.
• They are placed at each side of the spindle to reduce friction, ensuring smooth and precise movement.
• This enhances the instrument’s longevity and accuracy.