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vbOnline Tachometer Setup


What types of speed sensors can you use with a vbOnline device?


A single speed sensor is required for a typical machine installation. The many vibration sensors on the machine can all use 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. They 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 - See 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 several sensors - See the sensor data sheet.

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 to use with your vbOnline instrument. These sensors can be aligned to detect gear teeth, flange bolts, or shaft keyways. Some examples are detailed below*:

* Several manufacturers produce a range of different models of sensors. Select your sensor based on availability in your region and your specific requirements (environment, etc).

TTL Output

You can use your vbOnline with any sensor, encoder, or interface that outputs a digital signal (typically 5 V). Sensors may be installed by the machine manufacturer or signals may come from a control interface.

Switch Output

You can use normally open or closed switch contacts 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)


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, and vb8 portable instruments accept the same input signals. This means you can use the same sensors for the vbOnline. However, ensure you note the following points:

• Instruments SN below 40800 provide between 7 and 8.4 volt output for sensor power
• Instruments SN above 40800 provide 5 volt (TTL) output to the sensor
• All instrumnet only accept one pulse per revolution
• vb5 instruments do not support keyphasor sensors