vb Calibration Check

The information provided is for help with Commtest Instruments products:

• vb instrument

QUESTION

How do I check the calibration of my vb instrument?

ANSWER

You can check the calibration of your instrument by following the procedure below; however, re-calibration can only by performed by an authorized Commtest repair facility. USA and Canadian customers can have their instrument's calibration checked by the supplier at the end of this article. The FAQ article at this link explains how often the vb instrument and its accelerometers should be calibrated. To verify the calibration accuracy, perform the following procedure:

• Choose either vb channel 1 or channel 2 for the test.
• Set that channel to measure from a sensor with the sensitivity set at 100 mV/g.
• Set the instrument to take a reading using the velocity unit mm/s rms.
• Set the Fmax to 400 Hz.
• Connect the function generator lead to the instrument's BNC Connector.
• Set up the function generator to input a signal as follows:

100 Hz

0.3844 V AC (This is a nominal 3.844 g signal.)

12 V DC Bias

The resulting velocity reading should be 60 mm/s rms +/- 1% (59.4 to 60.6)

The above procedure will verify the calibration at one point, which is normally sufficient. Some customers may want a range of points checked. If so, when adjusting either the frequency or the voltage input, the resulting velocity reading can be calculated using the formula:

V = 1561 x (g/f)

Where:

V = Velocity reading expressed in mm/s

g = Acceleration expressed in gs (The g value is equal to the nominal input millivolts/100)

f = Frequency expressed in Hz

Note: At lower frequencies the level of the input signal will need to be decreased to keep the velocity output within its maximum range of +/- 100 mm/s.

This information combined with basic operation guidelines contained in the Instrument Reference Guide should be all that is needed to verify and certify vb instrument calibration.

USA and Canadian customers

Darlene Turner

Vibration Analysis Limited

1110 Morse Rd

Columbus, OH 43229614-476-0740

Vibration Analysis Limited provide a certificate of calibration and calibration sticker traceable to National Institute of Standards and Technology (NIST). All calibration is in compliance with ANSI/NCL Z540, ISO Guide 25, and MIL-STD-45662A.

FAQ ID: 11615 Last Reviewed: 26/09/2002