Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
2002-09-12
2004-11-30
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S039000, C702S064000, C702S083000, C702S094000, C702S104000, C073S001820, C073S602000, C073S624000, C073S627000, C073S862638, C073S001880, C073S129000, C324S207160, C324S613000, C324S608000, C417S012000, C417S018000, C417S053000, C340S650000
Reexamination Certificate
active
06826490
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a transducer calibration system and, in particular, to a transducer calibration apparatus and method for automating transducer calibration or configuration including transforming an output of a transducer and thus, the use of the transducer, from a first target object material used to calibrate the transducer to a second different target object material being subsequently monitored by the transducer.
BACKGROUND OF THE INVENTION
As is well known in the art, machinery protection systems are designed to employ a variety of transducers and display appropriate machinery parameters. Alarms are generated based on the measurements made by the employed transducers and when conditions exceed user-established limits the alarms can be used to automatically shut down the machine and/or to annunciate machinery problems to operators and other plant personnel.
Proximity probe protection systems which analyze and monitor, for example, rotating and reciprocating machinery are well known in the art. These systems typically include one or more proximity probes which can be defined as noncontacting eddy current displacement devices operating on the eddy current principle for measuring displacement motion and position of an observed conductive target object relative to one or more of the displacement devices. Typically, each proximity probe is located proximate a target object being monitored such as a rotating shaft of a machine, an outer race of a rolling element bearing, or a piston rod of a machine and is operatively coupled to signal conditioning circuitry which in turn is coupled to a monitor or analyzing apparatus for data reduction and display. By known techniques, these systems analyze and monitor rotating and reciprocating machinery for providing, inter alia, indications of incipient problems. A variety of proximity probes, signal conditioning circuitry and monitors are at the present time being sold by the assignee of this application, Bently Nevada, LLC of Minden, Nev.
Ideally, proximity probe systems are manufactured to meet published performance specifications. They have a specified linear range and an average scale factor over that linear range. Typically, transducers are calibrated or measured against a particular material and one common standard is for a transducer to be calibrated or measured against 4140 steel of which many rotating shafts are made.
However, there are cases where the material of a target object to be monitored by a transducer is not the same as was used to calibrate that transducer. For example, in reciprocating compressors piston rods are generally not 4140 steel. Notwithstanding the above, cost reduction, ease of stocking spare parts and logistics often dictate that a standard transducer (e.g., calibrated or measured against 4140 steel) be used. Hence, in order to use a standard transducer to monitor the movement of a piston rod, the linear range and average scale factor of the standard transducer when it is viewing the piston rod material must be identified and only then can the average scale factor and linear range be used by the monitor to accurately calculate piston rod movement.
The following discussion describes a current method of determining the transducer performance when different materials are used for the measurement target. A specific example of setting up a piston rod monitoring system will be employed in delineating the current method. When setting up a piston rod monitoring system the user must generate a transducer curve for the compressor piston rod. A precision micrometer can be used to run or generate a transducer curve and one such precision micrometer for generating a transducer curve for, inter alia, setting up a rotating shaft or a piston rod monitoring system is sold at the present time by the assignee of this application, Bently Nevada, LLC of Minden, Nev. under the name 3300 XL Precision Micrometer. This particular precision micrometer has collets to fit both metric and English 5 mm, 8 mm, 11 mm, and 14 mm probes and includes means for a removable target button.
When employing the 3300 XL Precision Micrometer the probe fits into a probe-mounting collet that holds the probe stationary. A specially made target button can be constructed of the shaft or rod material and can be attached to the micrometer shaft. As the user moves the micrometer, the target button is moved toward or away from the probe tip. The target button simulates the rod or shaft and it's proximity to the probe tip. The target button must be made of the same material as the piston rod or shaft that is to be monitored.
However, this method is problematic because in many cases the customer does not have a target button made of the same material as the piston rod or even the shaft. In that case, a shaft micrometer apparatus such as the one sold at the present time by the assignee of this application, Bently Nevada, LLC of Minden, Nev. under the name 3300 XL Shaft Micrometer can be used to run a transducer curve.
This particular precision shaft micrometer apparatus includes a strap which is attached to a mounting base through eyelets, is wrapped around the target (piston rod), and is tightened to hold the mounting base firmly in position. A probe-mounting collet holds the probe in the mounting base parallel to the micrometer. As the user moves the micrometer the probe moves toward or away from the target (piston rod). Thus, a proximity probe/transducer, signal conditioning circuitry, a shaft micrometer including mounting means, a monitor, and a multimeter can be employed as is known in the art and in accordance with the following procedure for generating the transducer system curve when viewing a piston rod.
First, the probe is mounted adjacent the target and the transducer system is zeroed by adjusting the probe in a probe adapter until its tip is flush with the target while the micrometer is at zero. A set screw in the adapter is tightened to hold the relative locations of the probe with the micrometer. For the first gap reading the micrometer is, for example, backed off 10 mils (or 250 micrometers) if using an 11 or 14 mm probe or it is backed off 5 mils (or 125 micrometers) if using an 8 mm transducer. The gap voltage is read from the multimeter and is recorded by hand in a gap voltage row of a table. The process is repeated until a predetermined number of gap voltages are recorded. Next, incremental scale factor values (ISF values) are calculated by taking the difference between adjacent gap voltages and dividing by, for example, 10 mils (250 micrometers) for 11 mm or 14 mm probes or dividing by 5 mils (125 micrometers) for 8 mm probes. The incremental scale factors are recorded. Then a graph is plotted of voltage values versus probe gaps.
Next, the user determines the linear range of the transducer from the information gathered according to the following criteria:
1) By visual inspection the user determines the endpoints of the linear area of the curve;
2) From these endpoints, an Upper Gap Voltage and a Lower Gap Voltage are determined for defining the outer edges of the usable range of the transducer and are preferably chosen from the incremental voltages listed in the gap voltage row;
3) Additionally, the user is suppose to verify that for the range identified the incremental scale factors are within 10% of the average scale factor (ASF). The ASF is defined as: ASF=|(Upper Gap Voltage−Lower Gap Voltage)|/Total Range, where the Total Range=Upper Gap−Lower Gap (in mils or micrometers). For example, if the Upper Gap Voltage is a negative 18.3 volts, the Lower Gap Voltage is a negative 4.1 volts, the Upper Gap is equal to 90 mils and the lower gap is equal to 20 mils then the Total Range is 70 mils (Total Range=90 mils−20 mils=70 mils) and the Average Scale Factor is 203 mV/mil (ASF=|(−18.3−−4.1)|/70=203 mV/mil);
4). If the less than or equal to 10% deviation requirement isn't met the user
Foster Ingrid M.
Hala Roger A.
Barlow John
Bentley Nevada, LLC
Bhat Aditya
DeBoo Dennis A.
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