vbOnline Tachometer Setup
QUESTION
What types of speed sensors can be used with a vbOnline device?
ANSWER
A single speed sensor will be required for a typical machine installation. The many vibration sensors on the machine can all obtain the machine's speed from this one sensor. This includes a machine containing a fixed ratio gearbox, drive belt or chain, where the different shaft speeds are all related to each other.
Supported Sensors
The input circuit is very flexible and accepts pulse signals from a wide variety of speed sensors.
The 12 V and Ground connections provide power to the sensor, if required (50 mA Max). These connections are not required for correct operation of the tachometer input.
For operation, a series of pulses must be applied across Tach + and Tach -. These inputs are optically isolated from the vbOnline circuit and accept the following voltage range: 0V...0.8 V = OFF, 2.5 V... 28 V = ON. An alternative voltage range is accepted for Keyphasor sensors, please refer to the Keyphasor section below.
Maximum Speed for Tachometer Input
vbOnline tachometer inputs accept a minimum pulse width of 0.1 mS* which calculates to a maximum 5000 Hz for a symmetrical wave form. (On time = Off time).
* This exceeds the specification of many sensors , please refer to sensor datasheet.
Max RPM is dependent on the pulses received per revolution.
- 5000 (Hz) / Pulses per Revolution * 60(s) = Max RPM
- @ 1 Pulse per Revolution => 5000/1*60=300000 Max RPM
- @ 121 Pulses per Revolution => 5000/121*60=2479 Max RPM
- @ 1024 Pulses per Revolution => 5000/1024*60=292 RPM
Hall Effect Sensors
Providing non-contact sensing of any ferrous target, the Hall Effect Sensor is the ideal sensor for use with the vbOnline instrument. These sensors can be aligned to detect gear teeth, flange bolts or shaft keyways. Some examples are detailed below*:
* Many manufactures produce many different models of sensors. Please select your sensor based on availability in your region and your specific requirements (environment etc)
TTL Output
Any sensor, encoder or interface that outputs a digital signal (typically 5 V) can be used by the vbOnline. Sensors may be installed by the machine manufacturer or signals may come from a control interface.
Switch Output
Normally open or normally closed switch contacts can be used to provide a suitable signal to the vbOnline. As physical movement is required, such contacts would normally only be used on slower machines. In addition switch fatigue and contact wear should be considered.
Optical Sensors
Both LED and Laser optical sensors are compatible with vbOnline instruments, providing an easy to install, non-contact sensor. However they are not recommended for permanent installation due to the need to keep optical elements clean. Some examples are detailed below*:
* Many manufactures produce many different models of sensors. Please select your sensor based on availability in your region and your specific requirements (environment etc)
Keyphasor®
A displacement probe may be used as a speed sensor by detecting a shaft keyway etc. The Sensor should be adjusted until output from the probe's driver/interface meets the levels in following voltage range: -6 V...-10 V = OFF, -14 V... -22 V = ON
vb Portable Instruments
vb5, vb6, vb7 & vb8 accept the same input signals, so the same sensors may be used as for the vbOnline however the following points must be noted:
- Instruments SN below 40800 provide between 7 & 8.4 volt output for sensor power
- Instruments SN above 40800 provide 5 volt (TTL) output to the sensor
- All instrumnet only accept 1 pulse per revolution
- vb5 instruments do not support keyphasor sensors