ST350 Strain Transducer 2/08 C o p y r i g h t © 2 0 0 8 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The ST350 STRAIN TRANSDUCER is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for thirty-six (36) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
ST350 Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. Introduction ...............................................................1-1 1.1 Typical Application .............................................................................. 1-1 2. Specifications............................................................2-1 3. Sensor Alignment and Installation .........................
ST350 Table of Contents B. ST350 Accuracy Verification .................................. B-1 B.1 Verifying the Accuracy of ST350 Strain Transducers......................... B-1 B.1.1 Introduction ............................................................................... B-1 B.1.2 Background................................................................................ B-1 B.1.3 Factory Calibrations................................................................... B-1 B.1.4 Temperature Effects......
Section 1. Introduction This manual provides information for interfacing the ST350 Strain Transducer to Campbell Scientific’s Dataloggers. Unless otherwise specified, all part numbers are Campbell Scientific's. This manual contains information on sensor specifications, operating principles, installation, alignment, and calibration. The multiplier and offset values given here are based on calibration data obtained from the Bridge Diagnostic’s Calibration Sheet (see example Appendix C).
Section 1.
Section 2. Specifications Effective gage length: 3.0 in (76.2 mm). Extensions available for use on R/C structures. Overall Size: 4.375 in x 1.25 in x 0.5 in (111 mm x 32 mm x 13 mm). Cable Length: 10 ft (3 m) standard, any length available. Material: Aluminum Circuit: Full wheatstone bridge with four active 350 Ω foil gages, 4-wire hookup. Accuracy: ±2%, reading individually calibrated to NIST standards. Strain Range: Approximately ±2000 εμ. Force req’d for 1000 με: Approximately 17 lbs.
Section 2.
Section 3. Sensor Alignment and Installation 3.1 Alignment The BDI ST350 will only measure strain in the axis in which it is aligned with, therefore the more accurate the alignment, the more accurate the measurements will be. The easiest way to align a transducer is to mark a “grid” type pattern for both the proper foot placement and measurement axis. First, locate the center-line of the gaging area in both the longitudinal and transverse directions.
Section 3. Sensor Alignment and Installation 3” SURFACE PREP. LOCATIONS FIGURE 3-2. Surface Preparation - Location 3.2 Installation Once surface preparation is complete, the transducer can be installed using the selected mounting technique (see Sections 5- Mounting of Sensors to Various Surfaces). The two marks 1.5 inches from the center-line are used to locate the transducer longitudinally; align these marks with the center of the transducer feet.
Section 3. Sensor Alignment and Installation 3.3 Adjusting Excessive Transducer Offset If it is determined that zeroing cannot be accomplished with the Wheatstone Bridge circuit, then it is possible that the transducer has either been damaged or deformed slightly. In many cases the deformation is caused by a thermal change in the gage due to weather changes, such as location of the sun. In this case, the offset can be adjusted by simply loosening one nut and allowing it to return to a “zero-stress” state.
Section 3.
Section 4. Wiring 4.1 Initial Check-Out Upon receiving new transducers, it is important to check that they are in proper working order. Using an ohmmeter, read the resistances between the black and red wires and then the green and white wires, both readings should be very close to 350Ω. If they are not, the unit may be unusable and should be returned to BDI either for repair or replacement.
Section 4. Wiring tension provides a positive output signal and compression a negative signal. If a tension force provides a negative signal (and vice-versa), the user should either switch the signal leads or make appropriate adjustments to the signal conditioning. NOTE Before going to the field, Campbell Scientific highly recommends that a simple validation be performed by the user to ensure that signal conditioning, gains, and calibration factors are being properly applied.
Section 5. Mounting of Sensor to Various Surfaces 5.1 General In most situations, other than reinforced concrete, the most efficient method of mounting a transducer is using the tab/glue method. This method is the least invasive and is truly a “non-destructive testing” technique. Below is an outline for implementing the glue/tab technique. Tips and alternative mounting techniques for different mounting surfaces can be found in the following sections. 1.
Section 5. Mounting of Sensor to Various Surfaces NOTE For closest Loctite Distributor call: 1 (800) 243-4874. Once testing is complete, carefully loosen the 1/4-20 nuts from the tabs and remove transducer. If one is not careful, the tab will pop loose from the structure (particularly when testing concrete structures) and the transducer may be damaged. Use vice grips to remove the tabs from the structure.
Section 5. Mounting of Sensor to Various Surfaces 5.2.2 Reinforced Concrete NOTE See “Instructions for Using ST350 Strain Transducer Extensions on Reinforced Concrete Structures” in Appendix A for extension attachment instructions and important information regarding the use of transducer extensions. 1. Examples: Bridges, building components (columns, joists, floor systems, etc), foundations, piles. 2. Methods for attaching the ST350 Strain Transducer to reinforced concrete: a. Tab/Glue: See above. b.
Section 5. Mounting of Sensor to Various Surfaces c. NOTE 5-4 - Tighten the washers against the concrete by twisting the nut with an open-end wrench. It is important to set the stud before attaching the extension to prevent damaging the gage. Once secure, leave the nut on the bolt to hold the washers in place. - Apply adhesive to the tab and push unit to mounting location. Pull back tab, leaving a patch of adhesive on the structure.
Section 5. Mounting of Sensor to Various Surfaces 3. - Slide the drilling jig over the stud and align it with the second hole location. - Drill the second 1/4” hole and follow the previous steps for securing the second concrete anchor. - Remove the washers and nut from this stud. - Slide the transducer end over the stud without washers and the extension end over the one with washers. - While holding the transducer assembly in place, screw nuts on the studs and tighten with an open-end wrench.
Section 5. Mounting of Sensor to Various Surfaces - When a transducer is attached to an extension it is significantly more vulnerable to damage. A five gallon bucket is a good way to transport multiple gages while extensions are installed. Put the extension downward into the bucket and loop the cable over the transducer to help prevent cable tangles. 5.2.3 Pre-stressed Concrete 1. Examples: Bridges, building components (columns, joists, floor systems, etc), foundations, piles. 2. 3.
Section 5. Mounting of Sensor to Various Surfaces - If the Tab/Glue method is being used ensure that the area is clean of dust before installing the gage. A can of compressed air or an air compressor is a great way to ensure a dust-free gluing area. 5.2.4 Timber 1. Examples: Bridges, building components (columns, joists, floor systems, etc), piles. 2. 3. Methods for attached ST350: a. Tab/ Glue: See above. b. 2.
Section 5.
Section 6. Calibration and Validation Calibration is performed on each sensor prior to shipping from the Manufacturer and a Calibration Certificate is shipped with each sensor. This certificate certifies that the sensor is traceable to NIST Standards. If this sensor is out of specification it can be sent to Campbell Scientific, Inc. for recalibration.
Section 6.
Section 7. Maintenance, Replacement Parts, and Repairs 7.1 Maintenance The ST350 Strain Transducer has been designed to minimize the amount of maintenance required to keep the transducers operational. Before each use it is recommended that every transducer be visually inspected for damage and powered on to ensure it is working properly. This should be done two to three weeks before the testing date in case any repairs are required.
Section 7. Maintenance, Replacement Parts, and Repairs FIGURE 7-2. Proper Connection to Data Acquisition System for Tension and Compression Debris and glue removal from foam areas between transducer body and lid: This area should be cleared of any debris or glue. The easiest way to remove any sort of obstruction from the foam area is by using a dental pick. Glue can be chipped away and debris, such as sand, can be pulled to the surface and wiped away.
Section 7. Maintenance, Replacement Parts, and Repairs transducer must have at least a one foot cable exiting the transducer body. This cable can be spliced to a new cable of the proper length. If a transducer is damaged beyond repair, the transducer will be replaced at a discounted price. Please contact Campbell Scientific's Customer Service Department to obtain authorization for return of the unit.
Section 7.
Section 8. Datalogger Programming This section is for users who write their own datalogger programs. A datalogger program to measure this sensor can be created using Campbell Scientific’s Short Cut Program Builder Software if using LoggerNet or by using PC9000 software for the CR5000 or CR9000X. Short Cut or PC9000 are used to create the datalogger program, the sensors should be wired to the channels shown in the wiring diagram created by either program.
Section 8. Datalogger Programming CallTable (MFGTRUSS) NextScan EndProg '***** Program End ***** 8.2 CR5000 Example 'CR5000 Example using Strain Transducer from BDI ST350 'CR5000 Program created using PC9000 (5.
Section 8.
Section 8.
Appendix A. Special Instructions for using ST350 A.1 Instructions for Using ST350 Strain Transducer Extensions on Reinforced Concrete Structures Special gage-lengthening extensions have been designed for use with the ST350 Strain Transducers in order to measure surface strains on reinforced concrete (R/C) structures. The aluminum extensions simply increase the transducer gage length to allow an “averaged” strain value to be recorded in the presence of cracks associated with most R/C structures.
Appendix A. Special Instructions for using ST350 very heavy, we recommend that the gain level for the STS be set to 500. It should be noted that in most cases, the live-load strain magnitudes recorded by BDI on reinforced concrete structures have been less than 100 με. TABLE A-2. Maximum Strain Ranges Multiple of Original Length Actual Gage Length w/ Extension Maximum Strain Range Approx. Conc. Stress for f’’c = 3,000 psi Approx. Conc. Stress for f’’c = 4,000 psi Approx. Conc.
Appendix A. Special Instructions for using ST350 4. Using an extension jig as seen in FIGURE A-1, insert a tab into slot. Set the transducer over the tab into the transducer hole closest to the cable exit and loosely thread on a nut. FIGURE A-1. Extension Jig FIGURE A-2. Drawing Extension Jig 1. There is a machined hole in the non-cabled end of the transducer that will capture a standard ¼ 20 hex head bolt (see FIGURE A-3).
Appendix A. Special Instructions for using ST350 from gage is used, the measurement from the hole closest to the cable exit to this hole is 24 inches. The next hole down the extension is 21 inches and so on. Using the tab jig, insert a tab into one of the slots and in the other the Extension Alignment Tab as seen below in FIGURE A-4. Insert the Tab into the hole marked with the desired gage length and the Extension Alignment Tab in to the hole next to it (see FIGURE A-5).
Appendix A. Special Instructions for using ST350 IMPORTANT: Once the extensions have been installed, the transducers are much more susceptible to damage during handling due to the large extension “lever”. To minimize possible damage, place the transducer/extension assemblies in a plastic five-gallon bucket with the extension ends down. This will allow for many assemblies to be carried at once and still be relatively protected. FIGURE A-6.
Appendix A. Special Instructions for using ST350 1965 57th Court North, Suite 106, Boulder, CO 80301-2826 Ph: 303.494.3230 Fax: 303-494-5027 www.bridgetest.
Appendix B. ST350 Accuracy Verification B.1 Verifying the Accuracy of ST350 Strain Transducers B.1.1 Introduction Often, our customers like to verify the accuracy of their new ST350 Strain Transducers, something that we encourage them to do. However, there are several pitfalls that can be made while trying to check these sensors out in the laboratory. Having fielded similar questions from several customers, we have assembled the following explanations to help avoid some of these problems.
Appendix B. ST350 Accuracy Verification differences in load (truck) placement. Thus, one can expect that every field test can have an error of two micro-strain. This, of course, is insignificant for quantifying the behavior of a large civil structure. B.1.4 Temperature Effects The ST350 Strain Transducers have been designed for recording Live Load strains only. Hence it is assumed that there will be little to no temperature change during any short time-span testing sequence.
Appendix B. ST350 Accuracy Verification Trying to measure the strain on a 2" wide strip of metal that is 1/8" thick and mounted as a cantilever beam is not a good verification test for these sensors. The primary problem with a thin bending specimen is that a large degree of curvature is required to obtain a small level of surface strain. In other the words, the transducer will simply be bent rather than elongated.
Appendix B. ST350 Accuracy Verification BDI addresses strain measurements on reinforced concrete is to use gage extensions, effectively amplifying the strain over anywhere from two to eight gage lengths, then taking an average. We accept the idea that concrete strains are not as accurate as those taken on steel structures, and attempt to maximize the accuracy with the gage extensions. This approach amplifies the signal, thus also improving the signal to noise ratio.
Appendix B. ST350 Accuracy Verification Magnitude of Applied Loads: Calibration tests should always be run up near the maximum safe linear range of the system. This will give the required confidence that the outputs from the transducers are indeed linear over the range of stresses of interest. Recording Data: It is VERY important to record the data continuously, rather than discreetly.
Appendix B.
Appendix C. Calibration Sheets C.1 Example of Calibration Sheet — BDI Supplied FIGURE C-1.
Appendix C. Calibration Sheets C.2 Example of Calibration Sheet — CSI Supplied Certificate of Calibration CUSTOMER: Company Name: Campbell Scientific, Inc Street/City/State: 815 W 1800 N, Logan, UT 84321 CSI Sales No.
Index A I Adjusting Excessive Offset .................................. 3-3 Alignment ST350................................................. 3-1 Alternative Mounting Techniques – ST350 ......... 5-1 Appendix A Attaching the Concrete Extension....................A-2 Recommended Gage Length Limits.................A-1 Using ST350 on Reinforced Concrete .............A-1 Appendix B Accuracy Verification for ST350.....................B-1 Background ......................................................
Index S Sensor ST350 Adhesive Information....................................... 5-1 Adjusting Excessive Offset .............................. 3-3 Alignment......................................................... 3-1 Alternative Mounting Techniques.................... 5-1 Calibration and Validation ............................... 6-1 Compliance Statement....................................... 3-3 Excitation Voltage............................................ 4-1 General ...................................
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