A sensor generally measures 95% of what it’s capable of measuring in line with the sensor. Two common types of vibration sensors are:
Single axis accelerometers
So which one is best for your application?
A single axis sensor simply measures vibration in only one axis, so the sensor can be moved to the direction or axis of interest to be measured. A triaxial sensor has three sensors built into one housing and therefore can measure three axes or directions without having to relocate the sensor, as with a single axis sensor.
Image Courtesy of Connection Technology Center, Inc. – CTC
All data systems on the market today will use a single axis sensor, however, some are also capable of utilizing a triaxial sensor but not all three channels at once. Some two-channel instruments can use a triaxial sensor but they will only process two axes at one time then take the third axis reading. To collect all three axes simultaneously you need a true three-channel (or greater) analyzer. For example, the VIBWORKS vibration instrument allows for both triax and single axis data collection. The VIBWORKS is a true four-channel instrument. Triaxial data collection can be a time saver when collecting large amounts of data, but as with all things there are pros and cons. Using single axis sensors would typically involve moving the sensor from the horizontal to vertical to axial positions at each bearing to collect the data. Using a triaxial sensor you place the sensor at the bearing and collect all three axes simultaneously. Drawbacks to triaxial sensor are the cost of the sensor and cable; the sensor alone can cost 3× or more the price of a single axis sensor. At some facilities that use a triaxial sensor they simply place the sensor at a single location on a machine and take the three axis readings and move onto the next machine. Only if a problem is detected they return to the machine and take more precision data. The user must make sure the sensor is always orientated and placed the same each time readings are collected as the sensor has three axes X,Y, and Z and if the orientation of the sensor is turned the trend of the machine data becomes skewed or void.
Condition Monitoring, Vibration Analysis by Gary James CRL