Sensor, accelerometer or transmitter?

What is the difference between an accelerometer and a vibration sensor? For specification in a vibration monitoring system the difference is only really one of language, but for those interested in a precise technical definition, read on.

A vibration sensor is a type of accelerometer but an accelerometer is not necessarily a vibration sensor.  An accelerometer measures a quality of acceleration, not necessarily vibration.  But vibration sensors, which measure a quantity of acceleration and are therefore a type of accelerometer, are by definition accelerometers.

A vibration sensor typically contains a piezoelectric crystal element bonded to a mass.  When the accelerometer is subject to an accelerative force, the mass compresses the crystal, causing it to produce an electrical signal that is proportional to the level of force applied.  The signal is then amplified and conditioned using inbuilt electronics that create an output signal, which is suitable for use by higher level data acquisition or control systems.

Having established the difference between an accelerometer and a vibration sensor, what then is a vibration transmitter?  This is an accelerometer that has been configured for loop-powered, 4-20mA output, which may be interfaced with many types of commercially available current-loop monitoring equipment, such as PLCs.  If you are using a PLC to measure lower value assets, such as motors, fans and pumps, a 4-20mA device with the capacity of interfacing directly into PLC, BMS, or SCADA offers a cost-effective means of online monitoring.