Vibration Measurement Basic Parameters

Vibration Measurement Basic Parameters

Do you notice why Vibration Measurement is so important? Many plants are in the process of changing their philosophy from that of shutting down a plant on a time scheduled basis to that of running the plant until the condition of the machinery indicates, it is time to shut down.

This condition is, of course, determined by instrumentation. This “predictive maintenance” philosophy is particularly applicable where the rotating machinery is the limiting factor in a plant maintenance schedule. Obviously this type of predictive maintenance program requires dependence upon instrumentation, and the proper interpretation of the data it provides. In this respect, it is important that all available parameters of vibration and rotor position are measured and evaluated. A simple investigation of amplitude and frequency alone does not, and will not, provide sufficient information about machinery performance to provide a strong, accurate predictive maintenance program.

Pleas check also: VIBRATION MONITORING SYSTEM

The following is a discussion of basic dynamic motion (vibration) and rotor position parameters that should be measured and analyzed in the diagnosis of rotating machinery in predictive maintenance programs;

DYNAMIC MOTION VIBRATION PARAMETERS

Amplitude

Amplitude of vibration on most machinery is expressed in peak-to-peak mils displacement. Amplitude, whether expressed in displacement, velocity, or acceleration, is generally an indicator of severity. It attempts to answer the question, “Is this machine running smoothly or roughly?”. The ability to measured the shaft with proximity probes has helped greatly in providing more accurate information with regard to the amplitude of the vibration. Today, most continuous monitoring of critical machinery is provided with a peak-to-peak displacement measurement either in mils or micrometers.

Frequency

The frequency of vibration (cycle per minute) is most commonly expressed in multiples of rotative speed of the machine.
It also provides an easy means to express the frequency of vibration. It is necessary only to refer to the frequency of vibration in such terms as one times rpm, two times rpm, 43% of rpm etc, rather than having to express all vibration in cycle-per-minute or hertz.

SYSTEM POWER UP INHIBIT (3300 Series)

The system monitor provide a power up inhabit function that allows each monitor to inhibit its alarms during power up or whenever a system voltage falls below its operating level. After power up, the inhibit function remains active for approx. 2 seconds.

SUPPLY VOLTAGE OKInput supply is 110/220 50Hz. We are using here 110 50Hz option and obtaining different outputs which are,

0/P voltage = -18 VDC (9000 series)

Seven LEDs located behind the front panel of the system monitor are ON to indicate when above mention supply voltages are functioning. Then a green LED on the front panel (Supplies OK) will lit.

SYSTEM RESET

The system monitor provide system reset capability that is activated by either external contact closer through terminals on the power input module or by pressing the RESET switch on the front panel.

TRIP MULTIPLY

It is activated by contact closure through terminals on the power input module. When activated, trip multiply allows the alarm set points to be multiplied by a factor preset on monitors with trip multiply option installed. The trip multiply function is indicated by a red led on the front panel.

Please check also: Vibration Rod drop measurement

OK RELAY

The system monitor drives an OK RELAY that is located on the power input module. The SPDT relay is used to indicate that the 3300 rack is in ok condition. The ok relay is set normally energized. The ok relay is deactivated either by the system power up inhibit signal from system monitor or by a not ok signal from the monitor.

ALARM SET POINT ADJUST

The system monitor has two switches on the front panel that adjust set point levels on each monitor. One switch is for upscale adjustments and the other is for down scale adjustments.

KEYPHASORS

The system monitor receives input from two-keyphasor transducers through terminals on the power input module and buffers the input for use by the monitors. Buffered keyphasor signals are also available from the coaxial connectors on the front panel. The system monitor also provides short circuit protected keyphasor power.

DIP SWITCHES FUNCTION FOR DUAL VIBRATION & THRUST CARDS

BA= Bypass Channel A
BB= Bypass Channel B
DB= Danger Bypass
AA= Adjust Channel A
AB= Adjust Channel B

Calibration Data for Vibration Monitor Cards

SCALE-FACTOR 200 mv/mil
lmil = 1/1000 inch= 25.4/1000 mm= 25.4 x 1000/1000 = 25.4 μm
1mil=25.4μm
1mil/200 mv = 25.4 μm
/200 mv
l μm  = 200/25.4 = 7.874 mv

lmil = 25.4 μm
1μm = 1/25.4 = 0.03937 mils
1μm = 0.03937 = 1mm = 39.37

Extension Cable
This is the piece of cable, which is used to complete the electrical length required by proximeter. Extension cable length option;
4.0 meter & 4.5 meter
8.0 meter & 8.5 meter
Armor option;
With out armor With armor
Extension cable physical length equals to the electrical length ± 10 %. Extension cable resistance is 3.1 to 3.5 Q (Internal) and external is 0.3 to 0.50.

Please check also: Installation-of-transducer-hardware-and-probe-installation

SAFETY BARRIER

This is the device, which provides intrinsically safe connection for transducers located in explosive atmosphere.