Measured variables

Noise

Microphones

Noise measurement is carried out using standard measurement microphones. Suitable microphones are those that contain the body of the microphone preamplifier and have power systems that are equipped with IEPE (ICP sometimes called). The choice of microphone depends on the desired range of measured sound pressure levels and frequency range. Normally, the sound pressure level is in the range of tens of decibels (dB) to about 140 dB and the frequency range from tens of Hz to a few tens of kHz. The microphone is connected to the system SAVAS using standard coaxial cables with BNC or SMB connectors. In dusty environments, it is necessary to protect the membrane of the microphone by a foam ball cap.

Inputs of SAVAS

The evaluation unit SAVAS system can work with any microphone, whose output signal has a voltage in the range of about + / -10 V. SAVAS is equipped with a power system circuit IEPE (ICP sometimes called) that can supply the preamp signal cable sensors, microphones and typically accelerometers. A variant of the SAVAS is based on the CompactRIO platform providing a dynamic range of input channels of about 100 dB based on PCI and PXI platforms with which it is possible to achieve a dynamic range up to 120 dB.

Evaluation

From the raw measurement signal a number of signal parameters are evaluated. These include:

  • The total RMS value of the signal (usually a sound pressure level in dB)
  • Octave spectrum
  • FFT spectrum
  • The envelope curve RMS values
  • Damping factor (for shock phenomena)

The decision on whether the test product is good or bad can be based on an evaluation of the absolute measured values ​​or evaluation of relative values ​​with respect to values ​​measured on the reference product.

 

Vibration

Vibration Sensor

Vibration measurements may be carried out by means of accelerometers, whose output signal is proportional to the detected acceleration. In discrete manufacturing it is sometimes a disadvantage to make mechanical contact between the accelerometer and tested product. Therefore, it is sometimes convenient to use the (more expensive) alternative of non-contact measurement with laser sensors. The output variable is a voltage proportional to the detected displacement. If this voltage is in the range of + / -10 V, it is possible to direct a laser scanner connected to the SAVAS system.

The values ​​of the measured vibration range from fractions of G to tens of G. The measured vibration frequency is commonly in the range from individual units of Hz to tens of kHz.

Inputs of SAVAS

The SAVAS system evaluation unit can work with any accelerometer or a laser distance sensor, whose output signal is a voltage in the range of about + / -10 V. SAVAS is equipped with a power system circuit IEPE (ICP sometimes called) that can supply the preamp signal cable accelerometers. The laser distance sensor must have its own external power supply. A variant of the SAVAS based CompactRIO platform provides a dynamic range of input channels of about 100 dB based on the PCI and PXI platforms with which it is possible to achieve a dynamic range of up to 120 dB.

Evaluation

 A number of signal parameters can be evaluated from the raw measurement signal. These include:

  • The total RMS value of the signal
  • Conversion between acceleration, velocity and displacement of vibration
  • Octave spectrum
  • FFT spectrum
  • The envelope curve RMS values
  • Damping factor (for shock phenomena)

The decision on whether the test product is good or bad can be based on an evaluation of the absolute measured values ​​or evaluation of relative values ​​with respect to values ​​measured on the reference product.

 

Speed

The system supports SAVAS speed measurement using different types of sensors:

  • The encoder
  • Tacho
  • The laser sensor
  • Magnetic field sensor

The encoder and tachometer are standard sensors but require a mechanical connection to the shaft of a rotating object. This is not always possible, therefore you need to use non-contact speed measurement with laser sensors or magnetic field sensors.

Inputs of SAVAS

SAVAS can provide digital inputs, TTL logic or 24 V DC for processing signals from the encoder and laser sensors. For tachodynamo or magnetic field sensors analog inputs are used.

Evaluation

The evaluation of the measured speed using sensors with digital output is done by counting pulses from the sensor for a certain period of time or the internal time base generator generates pulses which are counted within the duration of the sensor pulse.

The signal from the tacho has the character of a DC voltage directly proportional to the speed, so the SAVAS system voltage value is converted to a speed value by multiplying a constant.

The magnetic field sensor generates an AC voltage proportional to the change of the magnetic field caused by rotation of the magnetic parts, such as an electric motor. The SAVAS system detects the dominant frequency of the voltage and converts it to speed.

The SAVAS system uses the speed value to confirm that the rotating part of the test product rotates at the prescribed speed. If this speed is achieved, you can run the measurements of noise or vibration.