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

• The rotation of the coil in a PMMC meter is mainly controlled by Spring tension.
• Current creates a force that rotates the coil, but the springs pull back.
• The coil stops when these forces balance, and the pointer shows the measurement.

• A PMMC meter’s scale is set based on how current affects the pointer’s movement.
• More current equals more deflection. The scale marks are placed by matching known currents to their corresponding pointer positions.

The purpose of the jewel bearings in a PMMC meter is to decrease friction.

• Low-Friction Support: Jewel bearings, typically made of synthetic sapphire or ruby, provide a low-friction surface for the pivot to rest on. This ensures smooth and accurate movement of the pointer.
• Pivoted Coil: The coil is pivoted on jeweled bearings, allowing it to rotate freely.

• In a PMMC meter, the moving system is supported on a spindle with tapered and polished ends.
• These ends rest in hollow-ground bearings. The primary purpose of this design is to minimize friction.
• Reduced friction improves the meter’s accuracy and sensitivity, enabling it to measure even small currents effectively.

• The purpose of damping in moving coil meters is to control the pointer’s movement, allowing it to settle quickly.
• Without damping, the pointer would oscillate due to inertia, making readings difficult.
• Damping reduces these oscillations so the pointer can reach a steady and accurate reading faster.
• Eddy current damping is commonly used, where a conductor moving in a magnetic field induces a current that opposes the motion.

• In PMMC (Permanent Magnet Moving Coil) instruments, the aluminum frame on which the coil is wound often provides the damping function.
• As the coil moves in the magnetic field, eddy currents are set up in the aluminum frame or core, which opposes the motion of the coil.
• This results in the pointer slowing its swing and coming to rest quickly with minimal oscillation.
• The damping torque ensures the pointer reaches an equilibrium position on the scale, providing an accurate reading. Eddy current damping is commonly used in PMMC instruments

• The purpose of calibration of instruments is to ensure the instrument provides accurate readings over time.
• Calibration involves comparing an instrument’s output to a known standard to ensure it operates safely and efficiently.
• This process helps to eliminate errors, ensure measurement accuracy, and maintain the reliability of instruments.
• Over time, wear and tear can cause measuring devices to degrade, so regular calibration is essential to maintaining accuracy.
• Accurate measurements improve product quality, safety, and regulatory compliance

An instrument’s readings can change over time, even if the instrument itself isn’t faulty, due to the following reasons:

• Changes in temperature: Temperature variations can affect the physical properties of the instrument’s components, like resistance or dimensions, leading to altered readings.
• Aging of the instrument’s components: Over time, components can drift in value (e.g., resistors changing resistance, springs losing tension), affecting the instrument’s accuracy.
• Changes in the measured quantity: Even if the instrument is perfectly accurate, the readings will change if the quantity being measured changes. This is not a fault of the instrument, but rather a reflection of the changing conditions.

Calibration is a two-step process: First, you compare the instrument’s readings to known, accurate standards. If the instrument is off, you then adjust its internal settings until its readings match the standards. This ensures the instrument provides accurate measurements.

• The Potentiometer method is a fundamental way to calibrate voltmeters and ammeters.
• It uses a potentiometer to precisely measure voltage or current, which is then compared to the reading of the instrument being calibrated.
• Any differences are noted and corrected.
• It’s considered fundamental because it relies on direct comparison against a known, accurate voltage standard.