Vibration testing systems: start-up and commissioning
Vibration testing system is a complex technological unity, which includes high-capacity equipment. For error-free operation of the system in the course of start-up and commissioning activities, it is necessary to control a wide range of parameters, some of which will be considered in the present article.
Insulation resistance control
Prior to installation of the system, it is necessary to check the resistance of insulation between the coils of cooling fan motor, armature coil, and magnetic coil.
The values are to be checked by the insulation meter at the test voltage of 500V.
Insulation resistance values should be more than 10 MOhm.
In the case, if the insulation resistance values are below 10MOhm, the component should not be integrated in the system unless the reason of resistance decrease is found.
Grounding resistance control
Upon completion of the system elements installation, and prior to power supply activation, it is necessary to measure the grounding resistance level.
All system elements should be connected to the grounding bus, located below amplifier’s rack, and the resistance level should not be more than 0,5 Ohm (the only exception is the resistance level of shaker and amplifier grounding, which should not be more than 0,05 Ohm). The resistance level between the grounding bus of the amplifier and the electrical cabinet should not be more than 0,05 Ohm.
Accelerometers mounting control
Accelerometers should be mounted on the shaker table with the use of dielectrical material, so that to prevent electrical contact.
In order to check, that there is no electrcal contact, it is necessary to measure the resistance value with multimeter.
The measured resistance value between shaker table and accelerometer body, should not exceed 10 MOhm.
Voltage drop control between neutral and grounding lines
Voltage drop between neutral and grounding lines should not exceed 2V AC.
System power supply: voltage and current level control
Voltage and current levels of the shaker’s power supply are to be controlled at the connection point of the power supply cable inside of the electrical cabinet. For the purpose of controlling three phases of the system, there are used galvanically separated instruments for measurement of the power voltage and consumed current.
This control procedure is to be implemented throughout the entire period of start-up and commissioning works.
Power amplifier voltage control
The control is to conducted based on the readings of the DLU.
The voltage values of the power amplifier during operation of the shaker should be within the limit specified in the operational documentation.
Cooling system operation control
The temperature is controlled by means of the digital indicator at the DLU.
The control is implemented by means of calculating the temperature increase per 1 kW of the consumed power in accordance with the following procedure:
- Check the temperature transducer value upon activation of the system (before applying voltage to the magnetic coil);
- Check the readings of the temperature transducer as the voltage is applied to the magnetic coil for 30 minutes;
- Calculate the temperature gain as the ratio of temperature difference to the power applied to the magnetic coil.
Control of the generated signal levels
This control procedure is applicable both to vertical and horizontal position of the shaker.
The control is implemented by means of comparing the source graphs of the generated signal (reference graphs), provided by the manufacturer for the maximal sine profile with frequency sweep to the graphs, received in the pre-test mode for random vibration in the particular frequency band at the set amplitude level (RMS of the generator).
In the case of considerable difference (more than 30%) between the forecast graphs and the reference graphs, it is required to find and to eliminate the reason of difference between the graphs.
Control by classical shock profile
For the control purpose, there are used galvanically separated current and voltage transducers installed at the connection points between armature of the shaker and shaker’s rack.
The control is implemented with the use of shock series (duration-3ms, follow-up frequency- 1Hz) with gradual increase of shock intensity (at the rate of 10%) in the range of 10%-100% of the maximal admissible shock impact level. At each stage of shock intensity increase, it is necessary to check the linearity of armature current level increase.
Armature current and voltage control
For the control pupose, there are used galvanically separated current and voltage transducers installed at the armature connection points in the amplifier rack.
The control is based on the analysis of current and voltage graphs registered in the sinusoidal vibration profiles with frequency sweep.
The current graph should not have significant oscillations (i.e., deviations from the constant level) in the course of shaker operation in the profile with constant acceleration level.
Current and voltage graphs registered in the pofiles with different equalization level should not be different from their typical shapes.