Standard Motor Catalog

Section TR Technical Reference Guide

MECHANICAL MODIFICATIONS BEARING - TEMPERATURE DETECTORS BTD’s are used to measure the temperature of bearings; these are precision, wire-wound resistors with a known temperature resistance characteristic. In operation, the BTD is usually wired into a specific type of circuit (Wheatstone bridge). The output of this circuit can be used to drive a meter, which has been calibrated, in temperature, or to operate a relay to sound an alarm or shut down the motor. These devices are available on 320-5013 frame motors. BTD’s are constructed using a fine, pure, metallic, spring like wire surrounded by an insulator and enclosed in a metal sheath. • 120 Ohm Nickel • 100 Ohm Platinum • 10 Ohm Copper BEARING THERMOCOUPLE A thermocouple is constructed of two dissimilar wires joined at one end and encased in a metal sheath that an electro motive force (EMF) is developed by the thermoelectric effects. Any given set of thermocouple wires have a known “EMF vs. Temperature” characteristic. The other end of each wire is connected to a meter or measuring circuit. Heating the measuring junction of the thermocouple produces a voltage that is greater than the voltage across the reference junction. The difference between the two voltages is proportional to the difference in temperature and can be measured on a voltmeter. Thermocouples are classified based on the materials used for joints, examples are: Iron Constantan - Type J Chromel Constantan - Type E Copper Constantan - Type T Chromel Alumel - Type K BEARING LIFE L 10 life is the basic rating life expressed in millions of revolutions or number of operating hours at 90% reliability. The bearing life, in hours for 90% reliability, for anti-friction bearings expressed as:

L 10a life = a1*a2*a3*L 10 Where:

a1 = adjustment factor for reliability a2 = adjustment factor for bearing materials a3 = adjustment factor for bearing operating conditions including adequacy of lubrication, cleanliness, temperature etc.

Generally a2 and a3 factors are combined and called as a23 - Combined Life Adjustment Factor. BRAKES Brakes supplied mounted on motors will be disc-type, spring set electrically released brakes manufactured by Stearns Electric Corp. at General Electric Company option. Brakes are available for motors in frames 143-445 only. Several factors must be considered when determining the correct brake for a particular application. Refer to General Electric, for ‘frames above 445’ and ‘Special brakes like Drum-Shoe/ Floor-mounted’. 1. Brake Torque As a general rule of thumb, the torque rating of a brake should, as a minimum, match the full-load torque of the motor on which it is mounted. This will provide ample torque if the brake is used for holding and will also provide a stop in approximately the same time as required for acceleration. Full-load torque can be calculated as follows:

5252 x Hp Full-load Speed

Full-Load Torque =

For applications involving high inertia load, fast stops or a stop within a given time limit, the brake should be selected on the basis of total inertia to be retarded. Brake rating may be calculated as follows:

WK² x RPM 308 x t

Torque =

Where:

WK² = Load inertia in lb-ft² RPM = Full-Load Speed in RPM t = Time, in seconds, to stop

L 10 = 1000000 60*RPM

n

* (C/P)

Standard brake torque ratings or continuous duty include: 6, 10, 15, 25, 35, 50, 75, 105, 125, 175, 230, 330, 440, 550 lb-ft. If the calculated brake torque falls between the standard torque values, specify the next higher torque.

Where: RPM = rotation speed C = bearing dynamic capacity P = equivalent radial load n = 3 for ball bearing and 10/3 for roller bearing

L 10a life is the rating life expressed in millions of revolutions or number of operating hours considering life adjustment factors for reliability, material and operating conditions.

TR.34

Data subject to change without notice. 02/23 • www.gemotorswolong.com