SM0486
c. Pickup Attachment. You attach the pickup to the part being tested so that
there is no loose motion between the part and the pickup.
The point at which
vibration is to be measured must be considered in the installation of the pickup
assembly. When desirable, the pickup may be secured to a rigid probe which can be
held manually Against the point to be checked. The weight of the pickup, or of the
pickup together with the probe, should be less than one-tenth the weight of the
vibrating member.
Weights heavier than one-tenth the weight of the vibrating
member will load the member and produce false readings.
d. Pickup Sensitivity.
(1) The pickup is designed for sensitivity along the axis of the magnet
assembly motion. In this respect, the pickup is sufficiently insensitive to motion
across the sensitive axis to be used to establish the angular orientation of a
plane of vibration.
When you attach a pickup, its installation on the Vibrating
member must be in alignment with the desired direction of measurement.
This
characteristic is important when you are attaching a pickup to a vibrating member
or probe.
(2) The output of this velocity pickup is fed to a-vibration meter which
interprets
vibration
characteristics.
Vibration
meters
require
periodic
calibration to insure the accuracy of their indicating devices.
The pickup
sensitivity (corrected sensitivity) must be known in millivolts per inch per second
when working into the 10 kilohm input resistance of a vibration meter.
If the
corrected sensitivity is not provided in the manufacturer's specifications, it can
be calculated by using the circuit diagram of Figure 2 and the formula which
follows:
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