Contact-type sensor

In a contact-type velocity sensor, the moving section has a probe on one side and a coil on the other side. The moving section is restrained by a spring so that the probe and coil move along the direction of the central axis, and the coil is positioned in a specific magnetic field. When the probe is pressed against a bearing outer race, the vibration of the outer race is transmitted to the coil, and the induced starting voltage of the coil becomes the sensor output. These applications require light probe pressure and high frequency characteristics. The ADS-12 and ADS-24 contact-type velocity sensors offer flat frequency characteristics up to 10 kHz when the probe pressure is set to 0.4 N.

The characteristics of an acceleration sensor are such that the sensor has to vibrate in perfect unison with the test object. When an acceleration sensor is pressed against a test object, it's not possible to specify sensitivity or frequency characteristics. For contact-type velocity sensors, on the other hand, sensitivity and frequency characteristics simply require consistent probe pressure.

Sugawara previously calibrated sensors using a 100 Hz, 0.8 G vibration generator. During those years, we called sensor output voltage "sensor sensitivity." The velocity of a 100 Hz, 0.8 G vibration is 12.486 mm/s. Defining this as usp, we currently express sensor sensitivity in units of mV/usp. The equivalent unit under the International System of Units is Vs/m. The units are related as follows: 1 Vs/m = 12.486 mV/usp. The sensitivity of the ADS-12 contact-type velocity sensor is 3 mV/usp (= 0.24 Vs/m), while that of the ADS-24 is 6.24 mV/usp (= 0.5 Vs/m).

To minimize the effects of the probe pressure of contact-type velocity sensor on the Anderon vibration of a test bearing, we recommend setting the probe pressure to a level below 1/10 of the pressing force on the bearing along the axial direction.