Vibration Analysis Specifications > Vibration Specifications Standards Setup Criteria

Vibration Specifications Standards Setup Criteria Instrumentation Requirements Vibration measurements will be made with an FFT analyzer. The type, model, serial number(s) and latest certified calibration date of all equipment used in the measurement of vibration levels for machine certification, shall be recorded and made available upon request. FFT Analyzer • The FFT Analyzer shall be capable of a line resolution bandwidth Df = 150 CPM for the frequency range specified for machine certification unless this restriction would result in less than 800 lines of resolution, in which case the requirement defaults to 800 lines of resolution. (Higher resolution may be required to resolve "Side Bands," or in Band 1 to resolve machine vibration between 0.3X and 0.8X Running Speed.) • The Dynamic Range shall be a minimum of 90 dB. • The FFT analyzer shall be capable of applying a Hanning window. • The FFT analyzer shall be capable of linear non-overlap averaging. • The FFT analyzer shall have anti-aliasing filters. MEASUREMENT SYSTEM ACCURACY The measurement system (FFT analyzer, cables, transducer and mounting) used to take vibration measurements for machine certification and acceptance shall have a measurement system. Amplitude accuracy over the selected frequency range as follows:    • For displacement and velocity measurements ±l0% or ±1 dB.    • For acceleration measurements ±20% or ±1.5 dB. Figure 1 Measurement System Frequency Response MEASUREMENT SYSTEM CALIBRATION Vibration equipment (transducer, preamplifier, FFT analyzer, recorder and connecting cable) used to take vibration measurements for machine certification and acceptance must be calibrated by a qualified instrumentation laboratory in accordance with Sections 5.1 and 5.2 of ANSI S2.17-1980 "Technique of Machinery Vibration Measurement" within one (1) year prior to the date of machine certification. Calibration shall be traceable to the National Institute of Standards and Technology (NIST) in accordance with MIL-STD45662 "Military Standard Calibration Systems Requirements" (10 June 1980) or latest revision. VIBRATION TRANSDUCERS An accelerometer shall be used in the collection of data for machine certification and acceptance. The accelerometer must be selected and attached to the machine in such a way that the minimum frequency (Fmin) and maximum frequency (Fmax) as specified in Section 9 or specified otherwise by the purchaser, are within the usable frequency range of the transducer and can be accurately measured (reference recommendations of pickup manufacturer and/or Section 6.3, ANSI S2.17-1980). The mass of the accelerometer and its mounting shall have minimal influence on the frequency response of the system over the selected measurement range. (Typical mass of accelerometer and mounting should not exceed 10 % of the dynamic mass of the structure upon which the accelerometer is mounted.) Reference Appendix for Dynamic Mass definition and Procedure to Determine Mass Effect Integration is acceptable as a means of converting acceleration measurements to velocity or displacement, or for converting velocity measurements to displacement. VIBRATION MEASUREMENT AXES DIRECTIONS Axial direction (A) shall be parallel to the rotational axis of the machine. Radial directions (R) shall be:    • at 90° (perpendicular) relative to the shaft (rotor) centerline. Vertical shall be in a radial direction:    • on a machine surface opposite the machine mounting plate. For motors or pumps that are end mounted, vertical readings shall be taken in a radial direction relative to axial readings on a surface opposite the machine to which the motor or pump is attached (reference Figure 2-b). Horizontal shall be in a radial direction:    • at a right angle (90°) from the vertical readings:    • In the direction of the shaft (rotor) rotation (Reference Figure 2a and 2b).    • For electric motors, the Electrical Connection Box (Pot Head) may be used as the horizontal location relative    to vertical (reference Figure 3). Other:    • Any radial direction other than Horizontal or Vertical (A) FOOT-MOUNTED Figure 2 Vibration Measurement Axes Directions (B) END-MOUNTED Figure 3 Vibration Measurement Axes Directions VIBRATION MEASUREMENT LOCATIONS Required measurement positions and orientations on a machine's surface at which vibration measurements are to be taken shall be determined by mutual agreement of the purchaser and the machine builder, and shall meet the following requirements: Follow the convention specified, unless specified otherwise by the purchaser. If an obstruction or safety prevents locating a transducer as specified, locate as close as possible to the standardized position. Measurement locations used for machine certification and acceptance shall be identified on the machine layout drawing and/or machine as mutually agreed upon by the purchaser and the machine builder. Vibration measurement locations shall be on a rigid member of the machine, as close to each bearing as feasible. Bearing housings, bearing pedestals, machine casings or permanently mounted pickup mounting blocks are examples of suitable mounting locations. Vibration measurement location shall NOT be on a flexible cover or shield such as the fan cover on an electric motor or a sheet-metal belt guard. Guarding must be designed to allow accessibility to all measurement locations In the event that vibration monitoring points will be rendered inaccessible after the machine is built or access to the measurement points would present a safety problem during measurement, the purchaser shall be contacted to determine if Permanently mounted transducers are to be installed. Measurement locations shall be numbered consecutively from 1 to N in the direction of power flow per the following: Position 1 designates the "out-board" Starting Power Point bearing location of the driver unit of the machine. Position N designates the bearing location at the "terminating" Power Point bearing location of the driven machine. (Reference Figure 3A and Figure 4) When a machine station consists of multiple components, such as two or more spindles, consecutive numbering of components shall be in the direction of process flow. (Reference Figures 3A and 3B). Figure 3A Order and Consecutive Numbering Sequence Figure 3B Order and Consecutive Numbering Sequence Measurement locations documented for certification and acceptance on the machine layout drawing and on any vibration data submitted shall follow the following convention:    • Station or Machine    • Component    • Position    • Orientation Reference Figure 3C Figure 3C Measurement Location Documentation Convention Other Component Symbols not listed above should be agreed upon by the machine tool builder and the purchaser on an as-needed basis. TRANSDUCER & MACHINE MOUNTING CONDITIONS VIBRATION TRANSDUCER MOUNTING At the designated measurement positions, suitable surfaces shall be provided such that the mounted transducer will attach securely. Hand-held pickups are not acceptable for measurement by this specification. For a magnetic base mounted transducer the location on a machine's surface at which vibration measurements are to be taken shall be machined, if necessary, such that the magnet base can be attached firmly without "rocking." For a stud mounted transducer the machine's surface at which vibration measurements are to be taken shall be in accordance with that specified by the transducer manufacturer (torque, grease, etc.) Designated transducer type to be specified by the purchaser. If an adhesive is used to attach either the transducer or a magnetic mounting pad, the upper frequency limit of the transducer shall be reduced by 20% of the manufacturer's stated resonance for "hard" adhesives and by 50% of the manufacturer's stated resonance for "soft" adhesives. Transducer manufacturer's specifications should be consulted. The vibration transducer as mounted must be such that the measurement system Amplitude accuracy over the selected frequency range equals or exceeds the requirements specified MACHINE MOUNTING Where a machine can be tested as an individual unit (e.g. motor, spindle, etc.) the machine must be mounted as specified Where an individual machine can be tested only as an assembled unit (e.g. motor/pump, motor/fan, etc.), the machine mounting conditions shall be as equivalent as possible/feasible to those to be encountered upon installation at the purchaser's site. Figure 4 Vibration Measurement Locations Motor - Gear Box Spindle System (e) Figure 4 Vibration Measurement Locations Continued TECHNICAL REQUIREMENTS VIBRATION MEASUREMENT UNITS Vibration data for machine certification and acceptance shall be expressed in the following measurement units: The "Peak" and "Peak-to-Peak" Vibration Amplitude Measurements will be a Calculated Peak not a True Peak. The Calculated Peak will be derived from the RMS level based on the following equations: Peak (P) = 1.414 x RMS Peak-to-Peak (P-to-P) = 2 x (P) = 2 x 1.414 x RMS If a "True Peak" is required, the units of vibration measurement will be designated by the words "True Peak". FREQUENCY BANDS The frequency range of measurement shall be divided into sub-groups called bands. The Fmin and Fmax for each band will be defined in units of frequency or orders of running speed of the machine.(Ref. Figure 5) Mandatory Bands Band 1 shall be (0.3 - 0.8) X Running Order Band 2 shall be (0.8 - 1.2) X Running Order Band 3 shall be (1.2 - 3.5) X Running Order Other Bands Bands 4 through N shall be defined by the specific machine tool application. Figure 5 Frequency Bands LINE AMPLITUDE ACCEPTANCE LIMITS For vibration level limits specified in terms of "LINE AMPLITUDE ACCEPTANCE LIMITS":    • A line of resolution will have a band width Df = 150 CPM unless specified otherwise, or unless the Df = 1500 CPM restriction would result in less than 800 lines of resolution over the frequency range specified for certification, in which case the resolution requirement will default to 800 lines. (Greater resolution may be required to resolve "Side Bands," or in Band 1 to resolve machine vibration between 0.3X and 0.8X Running Speed.    • The maximum amplitude of any line of resolution contained within a band shall not exceed the Line Amplitude Acceptance Limit      for the Band. BAND-LIMITED OVERALL AMPLITUDE ACCEPTANCE LIMITS For vibration level limits specified in terms of "BAND-LIMITED OVERALL AMPLITUDE ACCEPTANCE LIMITS" the Total vibration level "A" in a band, as defined by the following equation, shall not exceed the Overall Amplitude Acceptance Limit specified for the Band A = Overall vibration level in the Band Ai = Amplitude in the ith line of resolution in the Band (I=1) =The first line of resolution in the Band (i=N) = The last line of resolution in the Band N = The number of lines of resolution in the Band If the total energy in a peak is to be measured, a minimum of 5 lines of resolution must be used and the peak must be centered in the band. If a line of resolution is coincidental with the Fmin/Fmax Of two adjacent bands, that line of resolution will be included in the band having the lowest acceptance level limit. The amplitude range sensitivity of the FFT Analyzer shall be set to the maximum input sensitivity possible without overloading such that the actual measurement uses at least 80 dB of the Dynamic Range. Certification will be based on: • Hanning Window. • Four (4) averages (Linear non-overlapping). The transducer mounting shall be such that the measurement system Amplitude accuracy over the selected frequency range equals or exceeds the requirements. This may require the use of more than one accelerometer where potentially high frequencies might occur (such as gear mesh or harmonics of gear mesh) along with lower frequencies (such as due to unbalance, misalignment, looseness, etc.) ALIGNMENT All coupled rotating machines consisting of consecutive shafts connected through a coupling (whether rigid or flexible) shall be aligned within the tolerances specified by the purchaser in the "Request for Quote." If the Purchaser does not specify an alignment tolerance, the requirements of this Standard defaults to the tolerance limits specified in Alignment Specification Consideration shall be given to any "thermal growth" that may occur during the normal operation of the machine that would cause the machine to "grow out of alignment" to the extent that the alignment tolerances of this specification would not be met. BALANCING STANDARD KEY For rotating machines and machine components with a keyed shaft, balancing will achieved using a standard one-half key in the key seat in accordance with ISO 8821-1989. If a "full key", corresponding to the half key used for balancing, is not provided with the rotating machine, a tag, as shown below, will be attached to the machine indicating the dimension of the key used to perform the balance test. Figure 6 Balance Test Key Dimension The use of solder or similar deposits to achieve rotor balance is not acceptable. Any parent metal removed to achieve dynamic or static balance shall be drilled out in a manner which will maintain the structural integrity of the rotor. MACHINE QUOTATION, CERTIFICATION, AND ACCEPTANCE QUOTATION The Quotation shall specify that the equipment will meet the applicable vibration level limits in Section 9 of this Specification - or the vibration level limits specified by the purchaser in the "Request for Quote." The Quotation shall state the applicable specification vibration level limits being quoted. Any additional costs required to meet the specification limits shall be grouped in a separate section of the Quotation and titled "VIBRATION LIMITS." Costs must be itemized and sufficiently detailed to permit a complete evaluation by the Purchaser. MEASUREMENT REQUIREMENTS FOR MACHINE CERTIFICATION Vibration measurements shall: Be the responsibility of the supplier unless specified otherwise by the purchaser. Be performed by technically qualified person who is trained and experienced in vibration measurement. The technical qualifications of the person doing the vibration certification shall be submitted as a part of the machine vibration certification data. Be taken with the machine operating as specified in Section 9 Where "no load" is specified, no actual machining such as cutting, grinding, etc. is to be taking place during collection of machine vibration data. Where "rated load" is specified, rated operating load--either actual or simulated--will be applied during collection of machine vibration data. Prior to taking vibration measurements, the machine will be "run-in" until it reaches speed and thermal stability. Vibration data for machine certification shall be measured during "run-off' at the vendor's facility. Where it is impractical to set-up and test a complete machine at the vendor's facility, arrangements shall be made to perform the test at the purchaser's facility. Under this circumstance, shipment of the equipment does not relieve the vendor of the responsibility for meeting the specified vibration level limits. The purchaser shall have the option to verify vibration data of equipment during machine "run-off' at the vendor's test site prior to shipment The machine layout drawing shall be submitted as a part of the Machine Vibration Certification. Vibration measurement locations on the machine's surface at which vibration measurements are taken shall be designated on the drawing. At the option of the purchaser, Shaft speeds (RPM), gear type and number of gear teeth, gear mesh frequencies (CPM), bearing manufacturer's name, bearing type number and class, shall be identified on the machine layout drawing. Where gearboxes are involved, an insert such as illustrated in Figure 4-e shall be included on the machine layout drawing. ACCEPTANCE Authorization for machine/equipment acceptance based on the vibration limits of this specification requires signature by the purchaser's authorized representative. A copy of the acceptance must be sent to the plant's purchasing department before final acceptance is authorized.