TAPE EXTENSOMETER Model CONVEX-D. Roctest Limited, All rights reserved.

Transcription

1 INSTRUCTION MANUAL TAPE EXTENSOMETER Model Roctest Limited, All rights reserved. This product should be installed and operated only by qualified personnel. Its misuse is potentially dangerous. The Company makes no warranty as to the information furnished in this manual and assumes no liability for damages resulting from the installation or use of this product. The information herein is subject to change without notification. Tel.: ROCTEST (Canada, USA) (France) (Switzerland) E1062D

2 TABLE OF CONTENTS 1 PRODUCT INTRODUCTION TECHNICAL DESCRIPTION PERFORATED MEASURING TAPE AND REEL TENSION ADJUSTMENT KNOB DIGITAL INDICATOR TENSION ADJUSTMENT MODULE REFERENCE POINTS INSTALLING REFERENCE POINTS TAKING READINGS AND DATA COMPILATION TAKING READINGS SELECTING THE RIGHT INDEX HOLE SWITCHING INDEX HOLE TENSIONING ADJUSTMENTS DIGITAL INDICATOR DATA COMPILATION TEMPLATE FOR DATA COMPILATION DETAILED EXAMPLE FOR DATA COMPILATION TEMPERATURE CORRECTIONS MAINTENANCE CLEANING AND LUBRICATION VERIFICATION FRAME BATTERY REPLACEMENT MISCELLANEOUS CONVERSION FACTORS TEMPLATE FOR FIELD DATA SHEET E1062D

3 1 PRODUCT 1.1 INTRODUCTION The is a digital tape extensometer which quickly and accurately measures changes in distance between two reference points in any orientation. This design incorporates several improvements compared to other convergence instruments available on the market. 1.2 TECHNICAL DESCRIPTION The whole system comprises the following components: MAIN COMPONENTS (Tape reel not shown) Page 1

4 1.2.1 PERFORATED MEASURING TAPE AND REEL A perforated measuring tape is housed into a reel that is attached to the anchor block located on the main body. The tape is graduated in meters, centimeters and millimeters on one side, and in feet and inches on the other side. The index hole close to each two inches increment is imperial and the index hole closer to each 50 mm is metric TENSION ADJUSTMENT KNOB A tension adjustment knob is used in combination with a tension adjustment module in order to allow the user apply a constant and repetitive tension on the tape when alignment marks are aligned. The adjustment knob has a unique antibacklash tensioning mechanism ensuring a continuous accuracy in time. Page 2

5 1.2.3 DIGITAL INDICATOR A digital indicator has also been added in order to accurately read the relative change between two reference points. By turning the rotary protection drum, it is easy to get quick access to the digital indicator function keys through the opening provided for this purpose. ACRYLIC WINDOW In operation mode, the rotary protection drum is turned in such a way that the digital indicator is still readable but protected by a small acrylic window TENSION ADJUSTMENT MODULE The tension adjustment module comprises: A pivoting latch, to lock positively the tape, thus facilitating the instrument's handling. Alignment mark s magnifying module to optimize the visual alignment with two superimposed magnifying lenses. ALIGNMENT MARK S MAGNIFYING MODULE PIVOTING LATCH Page 3

6 1.2.5 REFERENCE POINTS The standard reference point consists of a stainless steel eyebolt attached to an anchor. The anchors, chosen to suit the application, are either groutable steel rebar anchors for installation in shallow drill holes, or expanding rock anchor bolts. The eyebolts can also be directly bolted or welded to structural steel beams. 2 INSTALLING REFERENCE POINTS A good anchoring of the reference points is required to reach the specified instrument accuracy. In soft fissured rocks and masonry, grouted anchors are recommended (Type A Refer to illustration from section 1.2.5). They are installed in drilled holes with a minimum diameter of 20 mm and a minimum length of 150 mm. The rebar anchor is grouted in the hole with an epoxy resin or a non-shrinking cement grout. For hard rocks and concrete, it is possible to use the expanding rock anchor bolts (Type B Refer to illustration from section 1.2.5). They are installed in a drilled hole with a minimum diameter of 13 mm and a minimum length of 35 mm. The rock bolts are secured by tightening down the bolt. The eyebolts must be locked in place with the lock nut against the head of the bolt or anchor. The precise alignment of the reference points is not required, since the tape extensometer can be used at an angle to the axis of the reference points. Page 4

7 3 TAKING READINGS AND DATA COMPILATION 3.1 TAKING READINGS Although simple, the requires a standard procedure in order to obtain reliable and precise measurements. The procedure below explains all the steps to achieve consistent measurements. 1. Reset (screw) the tension adjustment knob all the way in until the end stop is reached (screw the knob towards digital indicator). 2. Turn the rotary protection drum to access the digital indicator. Press the ON key (ON/OFF). Set the units (mm/inch) This sub-step is optional and should only be achieved when the zero set point has previously been altered. Press the "ZERO" key to reset the digital indicator to zero value (i.e. when the tension adjustment knob is completely screwed and has reached its end stroke). Note: Make sure the "ABS" key has not been pressed before trying to reset the "ZERO", otherwise it will not be possible to reset the zero without pressing again the "ABS" key. To check if the "ABS" key has previously been enabled, make sure the mention "INC" does not appear in the top left corner of the digital indicator. 3. Unscrew the tension adjustment knob (towards the reel) to its proper initial position, which have been pre-established according to the anticipation of movement direction (refer to the figure in section 3.1.1). 4. Flip the crank handle to unlock the reel. Release the tape by unlocking the pivot lock. 5. Secure the snap hook of the tape to the first reference point. Carry the towards the opposing reference point and secure the reel hook. Be careful not to bend or twist the tape to avoid false readings. 6. Wind the tape back with the crank to remove the sag and then pull the tape to insert the tightest index hole into the index pin without preloading the tensioning device. Secure the tape by closing the pivot lock. Refer to section for detailed instructions on how to select the right index hole. Page 5

8 7. Hold the main body of the with one hand and rotate the tension adjustment knob with the other hand until the tension reference marks are aligned. Slightly move the nose up and down a few times to balance the tensioning device and eliminate hysteresis. Readjust the tension marks with the tension adjustment knob if required. Refer to illustration of section to better understand how to correctly apply the tension to the tape. Note: Over tensioning the tape will result in loss of repeatability and accuracy. This step is essential for repeatable and accurate measurements. 8. On a field data sheet, identical as the one supplied in section 5.2, record the readings where the index pin was inserted in the tape, as well as the value from the digital indicator. 9. Take three consecutive readings following steps 7 and 8. Between each reading, reset measurements by releasing tension on the tape of about 6mm (1/4 in) on the digital indicator. 10. Remove the pivot lock and release the tension with the adjustment knob in order to be able to unhook the tape from the index pin. Remove the reel hook and wind back the tape as you go towards the other reference point where the swivel snap hook is located SELECTING THE RIGHT INDEX HOLE The tape extensometer comes with index holes punched every 50 mm or 2 inches. When the index hole is engaged and locked in the index pin, the is secured. The holes are punched at a precise distance, but can slightly vary. That is why it is important to set the right hole and always use the same hole at every measurement until full stroke is reached (50 mm MAX), then switch to the next index hole available. The tension adjustment knob has a full range of approximately 55 mm. For convention in operation mode, the adjustment knob is set at 0 mm when fully in (screwed) and close to 50 mm (and not 55 mm) when fully out (unscrewed). So, there is a 5 mm extra length stroke which is required to unhooked the tape from the index pin. If out of range, a part of the measurements will be lost when moving the pin to the next or previous hole. To avoid any measurement loss, record the first index hole and the digital indicator values as the initial reading. Then switch to the next hole and record again the new index hole and digital indicator values before the adjustment knob comes out of range. There might be some slight differences between both measurements. Before inserting the index hole, make sure the tension knob is properly set according to the anticipation of movement direction. Then insert the next index hole in the index pin so the tape is as tight as possible to cover maximum range. Page 6

9 If the expected movement direction is unsure, set the proper index hole so the tension adjustment knob sits at mid travel near 25 mm (look for reference line on the body or look at the illustration below to see the three different cases scenarios). If convergence is expected, set it closer to 50 mm (unscrewed), and if extension is expected, set it closer to 0 mm (screwed) to allow the maximum range for the next measurements with the same index hole. If getting close to one end of the tension adjustment knob, switch to the next index hole. A detailed example is available in section 3.2, which explains how to process data reduction. Refer to the illustration below to select the right index hole according to anticipation of movement direction. Page 7

10 3.1.2 SWITCHING INDEX HOLE As movement occurs, the tension adjustment knob will be screwed (or unscrewed) to readjust the alignment marks, thus the knob is getting closer to the minimum or maximum of its range. Before running out of range, it will be required to switch from the actual index hole to the new one. Before switching index hole, take a measurement from the actual one, and then switch to the next hole by following, once again, the reading procedure from section 3.1. There will be a slight offset between both measurements, which will be explicitly demonstrated with the example in section TENSIONING ADJUSTMENTS Tension the tape using the adjustment knob to align the marks. Refer to the illustration on the right to better understand the appropriate approach. Note: The accuracy of the is achieved through its design and its reliable components. On this new design, we have added a magnifying lens to help the user reach the required accuracy. Page 8

11 3.1.4 DIGITAL INDICATOR The digital indicator has an OFF/ON key. It also has a mm/inch key to switch from metric to imperial. A ZERO key allows the resetting of the digital indicator before taking a measurement. Finally, there is an ABS key used for absolute measurement (optional, according to the user s preferences). 3.2 DATA COMPILATION TEMPLATE FOR DATA COMPILATION Readings have to be recorded on a field data sheet supplied by the Roctest Group (refer to section 5 or to the Roctest Group website). Make a copy of the data compilation sheet before starting the convergence monitoring. When done, fill the Excel spreadsheet template which contains all the required formulas, including index hole offset compensations. This template is available by clicking the following link, under "": DETAILED EXAMPLE FOR DATA COMPILATION On the following page is a complete example on how to group and process field data. Two types of measurements are illustrated through this detailed example in order to achieve a final accurate reading between two monitored reference points: The first one is a standard measurement (without changing the index hole), The second one is the continuation of the previous standard example where an index hole offset is required. Reminder: Three successive readings are recommended, and the average is used to determine the final displacement between same reference points. To take the second and third readings, reduce the tension on the tape by turning the adjustment knob, and repeat steps 7 and 8 from section 3.1 TAKING READINGS. IMPORTANT: THE TAPE EXTENSOMETER IS DESIGNED TO MEASURE RELATIVE VARIATIONS IN DISTANCE, AND NOT FOR MEASURING ACTUAL DISTANCES. Page 9

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13 3.3 TEMPERATURE CORRECTIONS -The coefficient of thermal expansion for the steel tape. K tape = 11.6 x 10-6 meters / meter / ºC -The coefficient of thermal expansion for the the aluminium body of the Instrument. K body = 23 x 10-6 meters / meter / ºC The step below will show you how to make the temperature correction for the steel tape. If required a temperature correction can be done for the aluminium body of the instrument using the same method. Extensometer aluminium body length is approximately 445 mm. How to calculate the change in length of the steel tape: Length is the change in length of the tape due to temperature Tape Length is the summed of the readings on the instrument K tape is the coefficient of thermal expansion of the steel tape Temperature is the change in temperature T current - T initial Length = Tape Length x K tape x Temperature Corrected tape length = Tape Length + Length Exemple: Tape Length is 12.3 meters Temperature is 12 ºC K tape is 11.6 x 10-6 Length = 12.3 x (11.6 x 10-6 ) x 12 =0.0017m Corrected tape length = 12.3m = m Page 11

14 4 MAINTENANCE 4.1 CLEANING AND LUBRICATION Care should be taken to keep the instrument clean by wiping it with a cloth. Only the tape should be lightly oiled and wiped clean. Any other parts of the instrument (except the tape itself) must not be lubricated. A high quality lubricant has been applied at the factory prior delivery of the instrument on the adjustment knob mechanism and each sliding parts. 4.2 VERIFICATION FRAME An optional verification frame can be supplied. The frame is used to make sure the specified resolution and repeatability of the instrument remain unaffected by shocks, damage or wear. To take a reading on the verification frame, proceed as follows: 1. Attach the hooks on both the tape end and the extensometer head, to the two steel eyes of the verification frame. 2. Tension the tape using the adjustment knob so that the alignment marks are aligned. 3. Using the same field data sheet, note the readings from the digital indicator. 4. Repeat the previous steps (steps 2 and 3) three times and take an average of the readings. 4.3 BATTERY REPLACEMENT To remove the battery, hold the instrument with the digital indicator facing towards the floor. Then, remove the cover and battery using the gravity as help for manipulation. Use the same approach to put a new battery back in place (with the digital indicator facing towards the floor). Battery type: (SR V Silver Oxide Button Battery) Page 12

15 5 MISCELLANEOUS 5.1 CONVERSION FACTORS TYPE TO CONVERT FROM TO MULTIPLY BY LENGTH AREA VOLUME MASS FORCE PRESSURE & STRESS TEMPERATURE at 4 C Microns Millimiters Meters Square millimiters Square meters Cubic centimeters Cubic meters Liters Liters Kilograms Kilograms Kilograms Newtons Newtons Newtons Kilopascals Bars Inches head of water Inches head of Hg Pascal Kilopascals Kilopascals Kilopascals Inches Inches Feet Square inches Square feet Cubic inches Cubic feet U.S. gallon Can Br gallon Pounds Short tons Long tons Pounds-force Kilograms-force Kips Psi Psi Psi PsI Newton / square meter Atmospheres Bars Meters head of water Temp. in F = (1.8 x Temp. in C) + 32 Temp. in C = (Temp. in F 32) / E E6TabConv Page 13

16 5.2 TEMPLATE FOR FIELD DATA SHEET Page 14