Test Point Location
In general, it is desirable to locate the test transducer as close as possible to the bearing with solid metal between the bearing and the sensor. Avoid bearing caps, which are of thin metal and are thus poor conductors of vibration energy. If possible, pick test point locations so that there is no metal-to-metal joint between the bearing and the sensor. The joint between the end bell and stator housing of a motor is an example of this. Fan housings on the ends of motors are also to be avoided.
In general, it has been found that for motors of less than about 50 HP, one test point is adequate, but for motors over 50 HP, each bearing should have its own test point. In any machines that are especially sensitive to bearing damage, and bearing problems should be detected as early as possible, each bearing should have its own test point.
Another consideration in the integrity of the path between the bearing itself and the transducer: If the motor and bell is a solid casting, it will effectively transmit vibration with little loss of high frequencies, but if it contains one or more metal to metal connections, the high frequencies will be significantly distorted.
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