Westinghouse Modules 1C-,5X- Emerson VE-,KJ-
Honeywell TC-,TK- Fanuc motor A0-
Rosemount transmitter 3051- Yokogawa transmitter EJA-
The electrical resistance of a winding, at a specified temperature, is determined by the length, gauge and composition (i.e, copper, aluminum, etc.) of the wire used to construct the winding. The winding in the vast majority of industrial servomotors are constructed using film coated copper magnet wire. Based on the 1913 International Electrical Commission standard, the linear temperature coefficient of electrical resistance for annealed copper magnet wire is 0.00393/o C. Hence, knowing a copper winding’s resistance at a specified reference or ambient temperature, the windings at temperatures above or below this ambient temperature is given by: R(T) = R(T0)[1+0.00393(T-T0)] (eq a) Where : T = Winding’s Temperature (0 C) T0 = Specified Ambient Temperature (0 C).
Using equation (a), a 1300 C rise (1550 C-250 C) in a copper winding’s temperature increases its electrical resistance by a factor of 1.5109. Correspondingly, the motor’s mechanical time constant increases by this same 1.5109 factor while its electrical time constant decreases by a factor of 1/1.5109 = 0.662. In combination, the motor’s mechanical to electrical time constant ratio increases by a factor of 2.28 and this increase definitely affects how the servomotor dynamically responds to a voltage command. In consulting published motor data, many motor manufacturers specify their motor’s parameter values, including resistance, using 250 C as the specified ambient temperature. NEMA, however, recommends 400 C as the ambient temperature in specifying motors for industrial applications, Therefore, pay close attention to the specified ambient temperature when consulting or comparing published motor data. Different manufacturers can, and sometimes do, use different ambient temperatures in specifying what can be the identical motor.
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