This invention relates generally to the collection and analysis of machine diagnostic data, such as vibration data, temperature, and rotation speed.  More particularly, this invention relates to a wireless monitoring unit installed at a rotating machine for collecting and analyzing machine diagnostic data. 
Many types of machines are used in a production or manufacturing facility, such as in the production of consumer and industrial goods and in the delivery of basic utility services.  Because of the importance of these machines in meeting production and service requirements, taking a machine offline unexpectedly due to a failure can be costly.  Accordingly, it is desirable to implement an effective predictive maintenance program to keep the machines in good working condition.  Of concern is that a machine part that is moving or being moved against eventually may fatigue or otherwise become compromised or defective resulting in decreased machine performance and reliability.  Eventually if a deteriorating condition is not detected a failure may occur.  Examples of machines for which it is desirable to collect data for preventive maintenance are motors, pumps, generators, compressors, lathes and other machines having rotating or other moving parts, such as a shaft, rotor, or bearings. 
Most predictive maintenance programs include the periodic collection of machine data, such as vibration data, rotation speed, noise, and temperature.  Vibration data is sensed using an accelerometer.  Rotation is sensed using a tachometer.  Temperature is sensed using a temperature sensor.  Data acquisition previously has involved an operator carrying a data collection unit, sensors, and cables from machine to machine.  A sensor is mounted at a test point on a given machine, then coupled to the data collection unit by a cable.  The operator then operates the data collection unit to gather the data.  The operator performs a route of a facility to gather data from one or more test points of one or more machines.  Typically, the data then is uploaded from the data collection unit to a data analysis system where condition monitoring is performed, so as to provide early fault detection and efficiently schedule maintenance of a machine. 
Wireless sensors have reduced the need for an operator to carry cables along a data collection route, thereby making data collection more efficient and safer.  Wireless sensors even have been permanently installed at machine test points.  However, implementation of permanent sensors in an effective manner has been a challenge.  In particular, the operational demands of the sensors results in a significant drain on the battery, resulting in an undesirably short battery life.  Such compromised battery life has been an obstacle against achieving reliable data collection.  Further, reduced sensor accuracy when the battery power gets too low, along with missed fault conditions due to a failed battery are significant problems.  These problems have been addressed in an inefficient manner by changing the battery every few months.  Such frequent attention to the sensor unit by a technician on site severely compromises the benefit of having a permanently installed sensor unit. 
Accordingly, there is a need for a more efficient sensor unit that can effectively monitor machine diagnostics while being permanently installed at a machine.  These and other needs are addressed by various embodiments of the present invention.