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The parameters to be measured vary according to the type of measurement. By loading one of the setups supplied with the NoiseStudio software ("HA 3 AXES" or "HA SHOCK"), the instrument is automatically set for the execution of the most suitable measurement.
The measurement parameter will be the average acceleration on the measurement time, indicated by Aeq, with Wh frequency weighting.
Selecting the above setups, the Wh frequency weighting is applied to the acceleration level measured on the three axes of the right channel with the degree of multiplication k=1, as required by the norm ISO 5349-1.
The norm prescribes to consider the contribute of the three measurement axes for the purpose of determining the daily exposure, as outlined below:
The instrument automatically records the levels on the three axes and the summation vector level.
From this relation, you can get the frequency weighted daily exposure referred to the 8 hours of work, conventionally indicated by the symbol A(8).
Later in the guide, we reported the measurement results evaluation criteria and some calculation examples of A(8).
To perform the measurement, you also have to set, according to your needs, the following parameters:
The input gain (Menu >> Settings >> General >> Measures >> Input Gain): you can set the greatest value but this should not lead to overload, as shown below.
The Integration Delay (Menu >> Settings >> General >> Measures >> Integration Delay). Delaying the integration beginning allows stabilizing the signal and obtaining a more repeatable measurement. Usually 5 seconds are enough.
The Integration Interval (Menu >> Settings >> General >> Measures >> Integration Interval) can be used as a timer to automatically stop the measurement when the set time has elapsed. When set to zero, you can stop the measurement only manually.
The measurement duration is selected to determine the worker's exposure to vibration. To change the duration of the measurement interval, you can also press ENTER from the standard VLM page, until the "Tint" symbol is blinking. Then modify its value and confirm with ENTER.
To start the recording, press REC and START/STOP simultaneously.
At the end of the integration interval Tint, the instrument stops the measurement and prompts you to save the data: press SAVE.
The data saved in the memory can be downloaded to the PC using the NoiseStudio software (please see later in this guide).
The main problems encountered during measurement concern the connection cables between the accelerometer and the analyzer and the DC-shift phenomenon of the piezoelectric sensors.
The connection cable and relative connectors can be the source of problems if they are damaged. You should always check that the cable and connector are not subject to stress during measurement.
You should reduce to the minimum the cable oscillations by fixing the cable to the vibrating object as close as possible to the accelerometer.
You also need to reduce the possible electromagnetic interferences associated, for example, to the mains cables.
The connection cable between the accelerometer and the analyzer should never be parallel to a mains cable.
The DC-Shift phenomenon
The piezoelectric accelerometers are subject to the so called DC-shift phenomenon: an abrupt shift of the polarization voltage followed by a slow settling to the normal value. This effect occurs each time the sensor is mechanically overloaded by an acceleration peak.
This shift (DC-shift) is detected by the analyzer as a high acceleration value at very low frequency.
To reduce the problem, you may need to insert a mechanical filter between the accelerometer and the vibrating surface. The filter may be a simple coating of resilient material. This is compressed so as to transmit the frequencies without attenuation.
With the HD2030 analyzer you can spot this phenomenon using the octave and third octave band spectrum analysis.
The vibrations transmitted to the hand-arm system are usually produced by a rotating or oscillating movement at a certain frequency. The shift of the vibrating surface will be maximum at that frequency.
If the spectrum shows higher shift values at low frequencies, you probably have a DC-shift. The HD2030 is provided with a practical comparison feature for the frequency shifts to simplify the assessment of this phenomenon. Alternatively, you can record directly the signals of the accelerometers, so as to perform later the analyses and checks.
The polarization voltage of the accelerometers
Before performing the measurements, you have to check the accelerometers' polarization voltages. To do so, you only need to put the instrument in measurement mode, Menu >> Settings >> General >> System and check the polarization voltages Vpol of the 4 measurement channels. The correct polarization voltage is indicated by the accelerometer manufacturer and is normally between 8V and 12V.
A wrong polarization voltage could mean that the connection cable between the accelerometer and the instrument is faulty, or that there are contact problems between accelerometer, connection cable and analyzer.
Determination of the input gain
To determine the input gain correct value, you can perform a test measurement.
From an input gain of 20dB, you can perform a test measurement for a sufficient time to obtain a measurement representative of the characteristics of the tool being assessed.
If you do not see any overload indication, proceed with measurement. Otherwise, reduce the gain of 10dB and repeat the test.
If the overload indication remains, set a 0dB input gain.
If you still detect an overload, you should replace the accelerometer with one having a lower sensitivity.
Selection of the integration interval
The integration interval is set according to the working cycles of the tool being assessed.
If the tool vibrations remain constant, you may need few seconds to get a stable and repeatable measurement. On the contrary, if the vibrations vary according to the working cycles or the type of work, you need an integration time of many working cycles, to get repeatable measurements. Alternatively, you can sample, using short integration intervals, each working phase and calculate the average value by keeping in mind the respective execution times.
Later you will see some examples of typical measurements that you can actually encounter.
To display the acquired measurements, you should install the NoiseStudio software and then download the data.
If the software is not installed, click on this link: go to NoiseStudio installation.
If the NoiseStudio software is installed, and the download to the PC has been performed, you can display the results.
