Scantek Inc  //  Measure Vibration with a Nor140

Measuring Vibration Using the Norsonic Nor140

 

Introduction

 

The Norsonic Nor140 sound level meter can be used to measure more than just sound in decibels.  Among other things, it can be used to measure vibration in linear engineering units.  These engineering units can be anything the user selects such as m, m/s, m/s2, or g's. This involves a few steps:

 

1) Connect the accelerometer to the meter

2) Change meter’s reported units from dB (decibels) to EU (Engineering Units)

3) Adjust the sensitivity based on the accelerometer used

4) Turn off corrections

5) Change input mode to IEPE

6) Select metrics to log

7) Download data and convert to Engineering Units

 

All Norsonic Nor140 can be set to engineering units and use an IEPE input. Octave, one-third octave, FFT, or logging functions are separate options.

 

Step 1) Connect the accelerometer to the meter

 

Accelerometer

The Norsonic Nor140 may be used with either charge type accelerometers connected through the microphone preamp or with an IEPE or constant current accelerometer connected directly. This article will only cover the use of an IEPE-type accelerometer connected directly to the Norsonic Nor 140. Information on using a charge accelerometer can be found on page 162 of the Nor 140 manual or Norsonic’s “Application note: Measuring vibration using Nor140”.

Cables

The simplest cabling to connect a IEPE-type accelerometer to the Nor 140 is with the Nor 4571 Microdot (male) to Lemo (male) cable (pictured below) to directly connect an accelerometer to the microphone preamp connector of the Nor 140.

 

Nor 4571

 

 

 

Step 2) Change meter’s reported units from dB (decibels) to EU (Engineering Units)

 

To set the Nor 140 to display Engineering Units follow these steps:

 

A) Press the SETUP button. The display will now look like: Setup Menu of the Nor140
B) Press 1 on the keypad. The display will now look like: Instrument Menu of the Nor 140
C) Press 9 on the keypad. The display will now look like: Miscellaneous Menu of the Nor 140
D) Press 6 on the keypad. The display will now look like: Units Menu of the Nor 140
E) Press the down arrow button on the keypad. The display will now look like: Units Menu 2 of the Nor 140
F) Press ENTER until you are back at the measurement screen. Measurement Screen with Corrections

  

Step 3) Adjust the sensitivity based on the accelerometer used

 

A) First calculate the sensitivity to enter. For example if the accelerometer has a sensitivity of: Accel Sensitivity
I. If you want your engineering units to be “g” then the sensitivity to enter is: EQ 2
II. If you want your engineering units to be “” then the sensitivity to enter is: EQ 3
B) Then press the Cal button on the Key pad. The display will now look like: Cal 1

C )Use the keypad to adjust the sensitivity to the calculated value. Press ENTER when finished.  The display will now look like:

 

If a vibration calibrator is available, place the accelerometer on the calibrator and use it as you would an acoustic calibrator. Adjust the sensitivity until the correct calibration level is displayed. 

NorVirtual 41
D) Press ENTER until you are back at the measurement screen. Measurement Screen with Corrections

 

 

Step 4) Turn off corrections

 

 

A) Press the SETUP button. The display will now look like:  Nor 140 Setup Menu
B) Press 1 on the keypad. The display will now look like:  Instrument Menu of the Nor 140
C) Press 4 on the keypad. The display will now look like: Nor 140 Input Menu 1
D) Press 2 on the keypad. The display will now look like:  Nor 140 Corrections Menu 1
E) Use the arrow keys and the INC and DEC keys to turn off all corrections.  The display will now look like:  Nor 140 Corrections Menu 2

 

 

 

 

Step 5) Change input mode to IEPE

 

AFrom the Correction menu press Enter. The display will now look like:  NorVirtual 46

B)  Use the arrow keys and the INC and DEC keys to change the Input type to IEPE. The display will now look like:

 

Note: Older version of the Nor140 firmware will list ICP instead of IEPE

Nor 140 Input Menu 2
C)  Press ENTER until you are back at the measurement screen.  Nor 140 Measurement Screen

 

 

 

Step 6) Select metrics to log 

 

Set up the Norsonic 140 to collect your desired metrics as you would for acoustic signals.

 

Step 7) Download data and convert to Engineering Units

 

Data on the Nor 140 is stored in dB re 20 μ units (20*10-6 units).  Download the data from the 140 with NorXfer and export to Excel. To covert the data back to engineering units in excel use the following formula.

 dB to EU

 

 

Useful notes:

Prefix abbreviations

 

The Nor140 uses the follows prefix abbreviations in EU mode:

 

f 10-15 femto
p 10-12 pico
n 10-9 nano
u 10-6 micro
m 10-3 milli
k 103 kilo
M 106 mega
G 109 giga
T 1012 terra

 

Marks on the lower line of the display

dB

 The signal strength is indicated as a level in decibel. The reference level is

 normally 20 µPa for sound pressure levels.

EU

 Engineering unit: The signal strength is indicated in a generic linear unit. 

 The actual unit could be voltage referring to the voltage on the input 

 terminal or m/s2 if an accelerometer is connected to the input.

#

 Numerical keyboard. The number printed on the keys are entered if you

 press one of the keys on the keyboard

E

 A numeric value has been entered. The instrument expects that you press

 ENTER to confirm the number.

N/H

 Indicates Normal or High measurement range. (Polarization voltage

 dependant.)

?  A key is pressed that the instrument does not understand.

 

Additionally there are marks indicating the applied corrections found on the lower line of the display:

 

R  Random incidence correction ON
 W  Wind screen correction ON
 Preamplifier correction ON
 Self-noise correction ON
 Polarization voltage off - Electret microphone