Exercise 3 – Data validation

Data is the fuel of reliability improvement. This is especially true in condition based maintenance. This exercise will provide you with a deep insight into the value of good data practices, particularly regarding the records of the  as-found condition of physical assets.

 

 

Detailed Explanation

Steps to follow

1

In this exercise we will examine some of the data validation tools in EXAKT.

Download the wheelmotor oil analysis data from wheelmotor.zip. (Not necessary if you are working from the CD and have hit "Get/Init datafiles")

2

This is a check for logical (chronolgogical sequencing) errors. Examine the Data Check report. It will give you an overall picture of the sample, and indicate  errors such as missing beginning or ending events.

Start “EXAKT for Modeling”, (resize windows so that these instructions and the EXAKT window can be viewed simultaneously)File, Open, Navigate to locate the file Mar2004CRC_WMOD (in c:\Program Files\Exakt\tutorial3\Mar2004CRC_WMOD if you extracted it from the CD), Open, Modeling (on menu bar), Select Current Model, CBM Model: PHM(no OC), OK, Activate Left pane (by clicking on it), Edit, Check Database, Data, Scroll down and look at this report, Reduce and Close the Report

3

Executing the instructions on the right should give you the following screen.

 

A) Left pane, Open DataCheck table, double-click on “Description” column heading, View (menu bar), Inspections, Include Events View, OK

 

B) Arrange windows and panes so that the Inspections and Events window covers the top two-thirds of the screen and the DataCheck window the bottom third.  The top window should have four panes.

4

The tables and views are  all in automatic synchronization. This makes it easy to find and correct errors, as we shall see in subsequent steps.

 

EXAKT has no way of distinguishing between missing ending events and “temporary” suspensions[1]. Therefore you will see many requests to “Check whether this history is temporary suspended or "EF/ES" is missing.” The user makes sure that all such indicated records correspond to units that are operating currently. EXAKT will then consider that they are indeed temporary suspensions. Otherwise the message means that you are missing an ending event, either an EF or an ES. You must manually add the missing record. If the lifetime corresponding to the message is in fact on going at the moment, then you must ignore this message.

DataCheck Window

5

The 47th record of the DataCheck table has the description “This record can't be properly identified. It has the same Ident, Date, WAge, and Event as the previous record:Id=5503R 2, Date=...”

DataCheck window, scroll to Record 47 and place cursor in Ident field of Record 47.

6

Note that record (819) is flagged in the Inspections table and the Events table likewise has its pointer positioned at record 404.

Inspections window, widen the Date column so the full date is visible, scroll up 1 row on the scroll bar so that record 818 is visible

7

Note that record 818 corresponds to an oil sample taken on the same equipment on the same day. EXAKT is suspicious about this and is asking you to verify the dates and working ages for these two. Maintenance planning personnel tell us that record 819 must be an error. Therefore we may delete it.[2]

Delete record 819 (by selecting the row (with Al = 143) and hitting the Delete key).

8

Here is a similar type of problem. But in this case two samples have the same working age but different calendar dates. EXAKT is not pleased with this situation and is asking you to do something about it.  You need to check if the equipment was really idle for one month.

DataCheck window, record 53, Inspections window, scroll up one row so that records 6204 and 6203 are visible.

9

Thus, does one go systematically through the database records, as indicated by the DataCheck table, correcting the anomolies that are pointed out by EXAKT.

Do not bother making any more corrections for purposes of this exercise. Close the Inspections, and DataCheck windows.

10

After following the instructions on the right you will have reproduced the graph below

View, Cross Graph, maximize window, Table: Inspections, Horizontal: WorkingAge, Vertical: SI, Condition: Si<1000, Show

11

After following the instructions on the right you will have reproduced the following graph.

Horizontal: Fe, Vertical Si, delete “Si<1000”, Show, reduce, X

12

Examine the OutputVarScript. It uses a succinct data query language to conveniently transform combinations of existing covariates into new covariates for building and testing risk models. The “*(=, >, or < statement)”, shown on several lines of this program, is read “where statement true”. The statement of interest is the next to last:

CorrSi=Si*(Si<>900)+1.2*Fe*(Si=900);

It is telling the program to return the actual value of Si where Si <>900 and to use  1.2*Fe where Si=900.

Database explorer pane (left pane), OutputVarScript, X

13

After following the instructions on the right you will have reproduced the graph shown below.

Modeling (on menu bar), Create Model Input tables, Complete data, View, Cross Graph, maximize, Table: C_Inspections, Horizontal: Fe, Vertical CorrSI, Show, reduce, X

14

EXAKT handles events (such as oil changes, adjustments, alignments, calibrations and other minor maintenance) that impact condition data in a correct manner. The instructions on the right will display the table illustrated below. It is often useful to display the events and inspections in a single table. Note the regularity of the oil change events.

 

For a period of 5 months, From 7/6/94 to 11/21/94 no oil change (OC) events are indicated, where oil changes were performed previously about every month. We suspect that the oil changes occurred but were not reported.

Modeling (on menu bar), Select Current Model, CBM Model: PHM(with OC), OK, Activate Left pane (Database explorer pane), Modelling (on menu bar), Create Model Input tables, Complete data, Database pane, C_Inspections, Scroll to record 356, reduce and close the  C_Inspections table

15

Executing the instructions on the right will display a graph similar to that found on page.  One history falls outside the 5-95% lines, violating the estimate of the proportional hazard model. One of the lifecycles does not fit the model. Why?

Modeling (on menu bar), Select Current Model, CBM Model: PHM(noHistExcl), Submodel: FeCorrSed, OK, Procedures panel, Modeling, Weibull PHM, In Order of Appearance, close the graph

16

Follow the instructions on the right and when we scroll down to the last row, we see the history number (also shown below) of the offending history. The number is found to be 64.

Database pane, Residuals: PHM(noHistExcl)(FeCorrSed) #1”, click on the “Residual” column header to order the records by Residual, scroll down to last row, note the History Number of 64, close the table

17

History numbers (such as 64) are applied by EXAKT to the life cycles in chronological order. We must identify which life cycle of which unit is the offending one. Following the instructions on the right, we can find the history (life cycle) is the 2nd history of unit 5509R. (see dialog box to far right).

Procedures panel, Decisions, All Histories, Select History 5501L[1] (That is the first lifetime of the left wheelmotor of haul truck 5501), hit the DnArrow key 63 times, Close

 

We need to examine the cause of the offending history. The instructions on the right reproduce the table and graph below. From this Figure, we observe that the cause of offending history is the unusually high values of Fe and Si not explained by a failure event. A reasonable solution to obtain a better fit model is to assume that a maintenance event was not properly recorded and to exclude this history from the model.

View, Inspections, Include Events View, View by history, Select All, Uncheck, move all variables to “Unselect” position, move Iron and Si to “Selected” position (as shown in image on the  right), OK

 

 

Select 5509R[2]

 

Further details and background of this exercise can be found in the wheelmotors report.


[1] A temporary suspension is a cut off of a life time that is still ongoing. It has been “temporarily” suspended by the snapshot of the data at the time of analysis.

[2] Deletions and changes should always be carried out on a copy of the database. You should keep a record of all changes that you have made to the data then save the summary with the database as a dated version. It is convenient to do this on a read-once CD. That way you can easily go back to some previous version of the database if you have made changes that need to be reversed. These are proper work habits for modelers.