A jewel bearing is a plain bearing in which a metal spindle turns in a jewel-lined pivot hole. The hole is typically shaped like a torus and is slightly larger than the shaft diameter. The jewels are typically made from the mineral corundum, usually either synthetic sapphire or synthetic ruby. Jewel bearings are used in precision instruments where low friction, long life, and dimensional accuracy are important. Their largest use is in mechanical watches.
The other major use of jeweled bearings is in sensitive mechanical measuring instruments. They are typically used for delicate linkages that must carry very small forces, in instruments such as galvanometers (PMMC), compasses, gyroscopes, gimbals, dial indicators, dial calipers, and turbine flow meters.
1) Which bearing is supporting the shaft of moving coil assembly in a PMMC instrument?
Jewelled bearings
Related AC and DC Measuring Instruments MCQ with Answers
Permanent Magnet Moving Coil meter
A Permanent Magnet Moving Coil (PMMC) meter also known as a D’Arsonval meter or galvanometer is an instrument that allows you to measure the current through a coil by observing the coil’s angular deflection in a uniform magnetic field.
Square wave
A Schmitt trigger is a comparator (not exclusively) circuit that makes use of positive feedback (small changes in the input lead to large changes in the output in the same phase) to implement hysteresis (a fancy word for delayed action) and is used to remove noise from an analog signal while converting it to a digital one.
Square wave is generated in Schmitt trigger circuit.
Control grid
Control grid controls brightness of the image on the screen of oscilloscope.
Band 9
Band 9 is used for UHF in International Telecommunication System.
