Shaft guide alignment using a decelerometer

I work in an underground gold mine in the north of Darkest Peru. The company has recently commissioned an 800 metres long vertical shaft with the purpose to transport personnel, material and waste. It has four compartments, two for skips and other two for a cage and its counterweight. Since it was a new shaft we thought everything was in good working conditions but it wasn't the case because we found that there were friction between skips and their metallic guides in several locations along the shaft. This was causing rapid wearing of skips' roller guides (We had one roller guide completely worn out after just three days). There even were some places where friction was strong enough to produce sparks.

This situation frightened the mine's management people so experts were hired to look at this problem. Few days later we got the visit of two guys from Tiley Associates who performed a shaft guide alignment test using a decelerometer. The idea of the test is to correlate acceleration measurement vs shaft's depth. Places with high acceleration measurement are an indicator of guide missalignment. The following criteria is used to determine wether the situation is critical or acceptable.

• Critical guide missalignment: acceleration measurement is greater than 0.5g or lower than -0.5g. Requires to take immediate corrective action.
• Bad missalignment: acceleration measurement between -0.5g and -0.25g or between 0.25g and 0.5g. Corrective action should be scheduled during the next planned maintenance.
• Acceleration between -.025g and 0.25g can be taken as acceptable missalignment.

Note 1: This criteria is valid under the consideration that shaft's structural integrity is in good conditions. 

Note 2: g=9.8m/s2.

Our technicians used the information from the Tiley report to improve guide alignment and results started to show immediately: Smooth cage and skips movement, no sparks and a significant reduction of guide rollers wearing. With these results in mind, our company decided that alongside periodical Tiley assessment we should perform an internal assessment more often so any problem can be spotted while it is in its early stages. For that to be done a decelerometer has been bought. In matter of weeks we developed a template in excel that uses raw input data from decelerometer and shows acceleration vs depth which is valuable information when performing shaft inspection.

Raw data from decelerometer is given in the following format:

Station_code    GMS
Sampling_rate   50.000000
Start_date      23.05.2018
Start_time      18:10:35.000
Time:sec   X0HNE,g    Y0HNN,g    Z0HNZ,g
0.0000000000e+00 6.7869942000e-04 6.1697539000e-04 4.8637476000e-04
2.0000000000e-02 6.2969107000e-04 6.0955791000e-04 5.4756897000e-04
4.0000000000e-02 5.9445804000e-04 6.0002115000e-04 5.5737064000e-04
6.0000000000e-02 7.1790610000e-04 5.6717231000e-04 5.1789905000e-04
8.0000000000e-02 7.4996021000e-04 5.8041781000e-04 5.1339558000e-04
1.0000000000e-01 6.1141228000e-04 5.5710573000e-04 5.6372848000e-04
(...)

First 4 rows show information of the station, date, time and sampling rate. From the 5th row we can notice withdrawn data from the station: Time vector and gravity acceleration in X, Y and Z axes.

g vs depth graph

X and Y axes give information about lateral movement of skips along the shaft while Z axes provides vertical acceleration. Speed and position can be obtained by integrating and double integrating acceleration values. Some help and guidance can be found in this Wikihow post.

Knowing alignment conditions beforehand allowed us to do inspections in less time and saved us thousands on rollers replacements so implementing this activity is highly recommended.