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Accuracy and Standard of the M.C and M.I Instruments Accuracy It is the closeness with which an instrument reading approaches the true value of the quantity being measured. Thus accuracy of a measurement means conformity to truth. Accuracy in case of M.C Instrument: The accuracy of M.C instruments is of the order of generally 2% of full scale deflection because the torque to weight ratio is high in case of M.C instruments. These instruments are very accurate if design properly. Accuracy in case of M.I Instruments: M.I instruments are capable of giving an accuracy within limits of both precision and industrial grades. Modern well designed portable M.I instruments have a D.C error of 2% or less. The initial accuracy of high grade instruments is 0.75% for frequency between 25 to 125 Hz and 0.2% to 0.3% at 50 Hz. These instruments usually have less accurate. Standard M.C and M.I instruments are calibrated at the time of manufacture against a measurement standard. A standard is a physical ...

Temperature limit of coil Q) To which class of insulating material are the solenoids coils of contactors have to subject? What are their maximum permissible temperatures? ANSWER: The maximum permissible temperature of solenoid coils of contactors is 140 °C. Example: Siemens make 3TF,3TH contactors coil sustain upto 140 degree C. For these coils the maximum permissible temperature rise limit for coils in air according to class of insulating material is E = 100 K. Since this is a temperature rise in Kelvin, this value shall be added with the maximum ambient air temperature of +40 °C of the contactors as described in IEC 60947-4-1. The temperature rise limits applicable only if the ambient air temperature remains within the limits -5 °C to +40 °C. ......