Using Velocity and Displacement Transducers with the vb Instrument

The information provided is for help with Commtest Instruments products:

• vb instrument

QUESTION

Can I connect velocity or displacement transducers to my vb instrument? What settings should I use on the instrument and what units will the displayed values use?

ANSWER

vb3000 instruments that use firmware version 4.30 and higher can accept velocity and displacement transducers as well as other sensor types. Other vb instruments such as the vb2000, vb1000 and any vb3000 instruments running firmware versions prior to version 4.30 have an accelerometer input only. However, this is not a hardware limitation; any suitable voltage signal can be fed into the vb inputs but the instrument firmware is not configured to display the results.

It is possible to use other sensors provided you are only interested in the AC signal and you are prepared to let the instrument display the velocity or displacement signal incorrectly in units of gs.

Notes

• The maximum voltage swing permissible on the inputs is 1 V peak-peak.

• The inputs are AC coupled, so frequencies below 1 Hz are attenuated (see product specification sheet). This is significant for displacement probes, for which the DC position often contains important information.

How to use a Sensor other than an Accelerometer

• In the Sensor Setup Menu define a new sensor e.g. 'Velocity Trans'.
• Enter a Sensitivity e.g. 100 mV/g in place of 100 mV/in/s for velocity transducers or 200 mV/g instead of 200 mV/mil for displacement transducers (the instrument supports sensitivities between 8.5 and 2300).
• Set the Drive Current ON for ICP sensors (with 2 mA supplied) and OFF for other input types.
• Use the instrument in Acceleration mode, not velocity or displacement.
• Use units of gs. The correct values will be displayed but in units of g instead of in/s (or mil).
• To present a report to a customer, paste it into Word® and manually edit or obscure the units.

This work-around may not be suitable for all applications where velocity or displacement transducers would normally be used. However, this may be acceptable for in-house use, or for occasional use of sensors other than accelerometers.

MORE INFORMATION

Read the FAQ article Current Readings with the vb Instrument.

FAQ ID: 11627 Last Reviewed: 26/09/2005