MMF VM30-H, Инструкция по эксплуатации, Страница: 44 / 58

15. Calibration and Function Check
The VM30-H is supplied in calibrated condition. That means the displayed vibration is within
the tolerance range provided that the sensitivity of the used transducer was entered correctly.
When the instrument was purchased with one or two sensors, the sensitivities are stored in the
VM30-H memory. The entered transducer sensitivities can be found in the supplied calibration
certificate.
The calibration interval depends on the intensity of use. Metra recommends to recalibrate the
equipment every 1 to 2 years. You may send the instrument for recalibration to the manufacturer
or to an independent lab.
In addition to calibration the standards for human vibration measurement demand a regular
function check.
After changing the accelerometer, its sensitivities must be entered. When you connect the sensor
cable, the calibration menu will open automatically. There you can select between two sensor
types. These will be usually a hand-arm and whole-body accelerometer. After selecting the
sensor you may either skip the calibration if the sensitivities have already been entered or you
may calibrate the sensor in two different ways:
•
Sensitivity input as numbers in mV/ms
-2
for each axis
•
Calibration of each axis by a reference shaker which supplies a constant sinusoidal vibration
signal of known magnitude.
15.1. Entering Transducer Sensitivities
The menu for entering sensitivities opens either when you connect a transducer or when you
press the MENU key and select “7/8: Sensor”. After selecting the transducer to be calibrated,
answer the question “Edit this sensor?“ with “Yes”. Now you can select the nominal sensitivity
of the transducer. Nominal sensitivities of 1 and 10 mV/m/s - ² are available. Press OK and
choose the calibration mode “By transducer sensitivity”. Press OK again and enter the
sensitivities in mV/ms -2 from the supplied calibration certificate successively for X, Y and Z
using the ◄▲▼► keys. The permissible range is 0.800 to 1.200 mV/ms -2 and 8.00 to
12.00 mV/ms -2 respectively. An error message is displayed if higher or lower values are entered.
Enter a sensor name with up to 20 characters using the ◄▲▼► keys and confirm with OK.
The VM30-H may store the sensitivities of two transducers. You may check the entered values
anytime when you open the menu “7/8: Sensor”, choose “Edit this sensor?“, confirm the
nominal sensitivity by OK and choose “By transducer sensitivity”. If you do not want to change
the calibration values, only press the OK key.
15.2. Sensitivity Calibration by a Vibration Calibrator
The menu for mechanical calibration of transducer sensitivities may be reached either by
connecting a transducer or pressing the MENU key and selecting “7/8: Sensor”. After selecting
the transducer to be calibrated, answer the question “Edit this sensor?“ with “Yes”. Now you
can select the nominal sensitivity of the transducer. Nominal sensitivities of 1 and 10 mV/m/s - ²
are available. Press OK and choose the calibration mode “By vibration calibrator”.
The calibration feature of the VM30-H is based on a reference vibration signal of 10 m/s²
(RMS) with a frequency of 159.2 Hz. Several calibrators of this type are available, for example
VC2x series of Metra.
Calibration starts with the X axis. Mount the sensor facing towards direction X onto the shaker
head of your calibrator and switch the calibrator on. Contact Metra for suitable mounting
accessories. The VM30-H will now display the measured vibration level in m/s². Adjust the
display exactly to 10.0 m/s² by means of the ▲▼ keys.
Subsequently calibrate the other two channels in the same way.
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