© Measurand 2008

 

 

 

What is the recommended installation procedure for SAA?

Measurand has developed a small-bore casing method of installation as described in our installation manual. Installation technique depends upon:

 

• The expected magnitude of the deformation
• Soil conditions
• Whether or not the SAA should be retrieved
• Whether or not earthquake data is important

 

In all installations, if the SAA is not directly in a drilled hole in rock or concrete, we strongly recommend placing it in 27mm (1.049”) ID PVC electrical conduit. It is held snugly in the conduit by unique self-adjusting joints. If deformations are modest, the SAA can be pulled out of the conduit by hand. In these cases the conduit could be grouted into a larger borehole. If large deformations are expected, then it is recommended to use sand between the small-bore casing (conduit) and the larger borehole (usually lined with 2-4” (50-100 mm) casing).

 

Wet sand is easier to install than dry sand, but may be undesirable if earthquakes are to be measured, due to liquefaction. A summary of installation options is described in the following table

(1” PVC = 27mm, 1.049” electrical conduit):

 

Measurand can supply small-bore casing if required (it is more difficult to source in Europe). Before substituting, please consult Measurand first.

 

Is it possible to use SAA in soil saturated by water?

Yes. SAA’s outer covering is impermeable to water It has been pressure tested to 980 kPa in a 100 m water column. 1” conduit (either PVC electrical conduit or metal) is recommended for all installations since it serves as a pressure barrier when it is dry inside and allows us to use SAA to greater depths. The outer covering of the SAA must not be punctured at any time as this will allow moisture to penetrate and the performance of the SAA will be compromised.

 

What are the limits for length and number of sensors at large depths?

A standard SAA has one foot segments which contain sensors. Segments are grouped into groups of 8 called an octet. Each octet has its own microprocessor for handling data communication. Each microprocessor adds a load to the RS485 communications protocol used by the SAA. After approximately 200’ (61 m) of SAA, a repeater must be used to help compensate for the amount of information being sent.

 

Each joint of the SAA can support a 700 lbs. (320kgf) tensile force.  If the SAA is being hung, the weight of the array cannot exceed this specification. Each joint of the SAA can support 50 lbs. of compressive force. If the array is being anchored, the weight of the array cannot exceed this specification. The mass of an SAA per unit length is ~ 500 g / m (0.1 lbs / ft).

 

To avoid exceeding the above physical limitations, we recommend using several 1” (27 mm) casings to hold several arrays, and staggering the installation elevations of the arrays. The SAAs should be supported by stainless braid surrounding the SAA and extending it to the surface, or a combination of braid on the SAA and cable extending to the surface. Azimuth control, if needed, can be achieved by adding our magnetometer option to the bottom of each array. Otherwise, the software can be set to calculate magnitude of deformation without azimuth calculation.

 

 

Figure 1 Staggered SAAs for Monitoring Greater Depths

 

 

 

What is the accuracy and sensitivity of SAA in collecting data?

The SAA calculates the position of its segments progressively from one end (the reference end) to the other. Tilt of each segment is relative to the gravity vector, and is measured using a long-term averaging technique. This method provides absolute tilt at each segment to a high accuracy, uninfluenced by previous segments. Tiny, random errors in relative displacement between the two ends of a segment are propagated from one end of the array to the other. By nature, some errors will be positive, and some will be negative.

 

A long-term (1.5 year) study of several field arrays involving over 4000 wireless data collections shows the long term accuracy to be 1.5mm (0.06”) for 32m (104’) arrays, or approximately 0.047 mm/m = 0.005% for lengths near 32 m. This figure refers to the long-term ability to track deformations relative to a starting deformation.

 

Short-term resolution is 0.5mm (0.02”) for 32m (104’) arrays, or approximately 0.0017% for lengths near 32 m. This refers to the ability to track very small changes in deformation over a short time period (minutes or hours) relative to a starting deformation.

 

See SAA_specifications.pdf in the “downloads” section of our website for information on accuracy at other array lengths.

 

Another figure of interest is the long-term accuracy of reporting the “absolute” 3D shape (relative to the gravity vector rather than a starting shape). We know from the above that over a long time period (years) we can track the 3D shape to 0.005% (1.5 mm) if the length of the SAA is approximately 32 m. This gives us confidence in specifying an accuracy for the absolute shape of 1.5 mm at 32 m (the same as the long-term accuracy relative to a starting shape), so long as the absolute shape is defined as that of the center lines of the segments, not that of the outer coverings. The coverings of the array are not uniform to 0.005%, so will introduce errors in the “absolute” shape, depending on how the array is held to a comparison surface. However, it is rarely required to know the absolute shape to better than a few mm, so more detailed discussion of the “absolute shape” specification is more of an academic exercise than a real requirement.

 

 

Is it possible to reuse an SAA?

The SAA’s design and the recommended installation procedures allow it to be installed in the ground and later retrieved. By not having to be in a slotted casing like inclinometers, the likelihood of retrieval when deformation occurs is much higher. The current design of the SAA has jointed segments every 30 cm/1 ft. Because of this, the SAA is capable of being pulled through bent sections of the casing that is it installed in. Inclinometers are not as robust to such deformations since they are typically installed in 50 cm or 100 cm segments and require good alignment for the inclinometer to travel smoothly.

 

With proper care, an SAA can be reused for other applications. The following guidelines should be heeded:

 

– Do NOT bend the joints beyond 45°

– Do NOT exceed the maximum 700 lbs pull strength of the SAA

– Do NOT exert more than 50 lbs of compressive force on the array when inserting in a borehole

– Do NOT expose the protective covering of the SAA to abrasive materials

– Do remove sharp edges from pipe before installing a SAA

– Do inspect SAA for cuts or other damage before inserting into casing

– Do NOT pull on communications cable to remove an SAA. Pull on the SAA and the suggested webbing only

 

Most customers have been leaving the SAA installed at a location for a long period of time.They are receiving data on a daily basis for years at a time.

 

The New York State Department of Transportation and a geotechnical company in New York have successfully installed and later retrieved an SAA and used it at another site.

 

Installation methods can be suggested to ease in the retrieval of an SAA.

 

 

What mining software can use SAA-collected data?

SAA comes fully supported with software to process and view the data:

• 3D visualization is provided

• Processing settings can be selected

• Alarm settings can be configured

 

Acceleration and 3D position data can be exported in ASCII and Matlab formats for use with other applications.

 

Using the export facility available in Measurand’s software would be the best way to get data from the array into other mining software.

 

 

How durable is SAA and what is its life expectancy?

The accelerometers used in SAA are the best in the industry: Analog devices MEMS. MEMS accelerometers were developed for the automotive industry for airbag deployment and have a lifetime rating of 20 years because of the safety issues. Their lifetime is expected to be well beyond that when in the ground, due to lesser temperature extremes than automotive. MEMS accelerometers have no moving or sliding parts, only tiny pure-silica structures that bend slightly. They are rated to withstand 5,000-10,000 G (e.g. they easily withstand dropping on concrete floor).

Compromises to SAA’s lifetime typically are caused in its protective covering, which have been pressure tested to 980 kPa in a 100 m water column. A cut could lead to water intrusion. In any properly-executed installation, there will be no cuts. Current SAAs have waterproof bulkheads at both ends and every 8 segments.

 

The bulkhead at the cable end prevents water intrusion from a damaged cable. Again, properly-maintained and installed cables should not have water in them. Any SAA is repairable on an ‘octet basis’ (8 segments).

 

SAA has proven to outlast slope inclinometer installations due to its ability to withstand significant shear forces. SAAs installed over two years ago are still in operation today. In one aggressive slide area, the SAA has outlasted more than 17 manual inclinometer boreholes.

 

What services are available with SAA purchase?

Installation Services: For first time installations, Measurand recommends that installation staff from Measurand assist in on-site installation and training. Typically, installation assistance includes insertion of SAAs in small-bore casing, assistance with cabling, and commissioning of earth-station equipment. Training includes outlining the principles of installation, and overview of Measurand software. We recommend including installation assistance at the time of order.

 

Repair/Modification Services: An SAA can be returned to Measurand for repair. If an array is cut or overbent, normally the damage will be confined to one octet (group of eight segments). Other segments are protected by waterproof bulkheads at octet boundaries. Damage will be assessed and an estimate for repairs will be issued before repairs are undertaken. Arrays may be made longer or shorter at Measurand, on an octet basis.

 

Support Services: Measurand does not charge for standard support – question and answer type support. If an Earth Station is installed with a connection to Measurand’s central servers for data conversion and Internet access, yearly charges for data processing and wireless services apply.

 

What is the simplest SAA setup?

Field SAAs can be directly interfaced to a laptop or other PC using a serial interface kit available from Measurand. This permits real-time visualization of the array using SAARecorder, and export of data including vibration, absolute shape, and shape relative to a “starting” shape. Exports may be viewed in SAA3D, which enables viewing “deformation surfaces” and deformation vs. time.

 

An example of this setup is an SAA installed in a borehole and visited periodically to collect deformation data and compare it to a “starting” deformation.

 

What is a typical field setup?

A typical field installation includes an SAA connected to a data concentrator and wireless modem. Power is supplied by a solar panel and deep-discharge battery, enabling years of unattended operation. The data concentrator collects data and sends it by wireless ftp to Measurand servers. The data are translated into viewable form and made available to customers on the internet, using SAA3D, Measurand’s 3D deformation viewer. Normally the transmission is made every day, but this rate can be increased or decreased using the same wireless link. Similarly, frequency of collection, alarm limits, and approximately 17 other variables can be set wirelessly.

 

Options for field installations include extra cable for arrays (15 m, or 50’ are included with each array), a MUX switch allowing up to four SAAs to share the same wireless modem, various communication packages including one-year or multi-year cellnet service, installation and training package, and alternate short-haul or wired communication setups.

 

How much cable comes with an SAA and what does it do?

15 m (50 feet) of cable is standard with an SAA. The cable carries power to the array and communicates with the in-array microprocessors to obtain vibration or deformation data using the serial RS485 digital communication standard. Two wires handle power; another two handle all communication. The cable includes extra wires for increased current capacity and a shield drain.

 

How much cable may I add between an SAA and its data concentrator or a PC?

Since data are communicated digitally between the SAA and its computer, and the RS485 standard is used, long cables are possible. Without taking special precautions regarding power drop and communication limits, a typical 32 m (104’) SAA can have a cable at least 65 m (200 feet) long. With some modifications (wire size, type of cable), it is possible to extend the length to over 300 m (1000 feet) in many cases. SAAs have been operated at the end of a 1000’ wireline. We recommend always checking first with Measurand to review your cable requirements. Some attention must be paid to shielding and/or twisted pairs.

 

What about lightning strikes?

Measurand shall not be responsible for lightning damage to equipment or personnel. To minimize risk of lightning damage, ensure that the cabinet containing Measurand equipment is metallic and grounded to a specification at least as stringent as that for grounding of domestic or industrial electrical entrances in the jurisdiction of the equipment location. It is further recommended that cables between the cabinet and Measurand sensors be contained in grounded metallic conduit. Additional protection may be obtained by installing grounded conductive rods near any exposed equipment, the rods extending at least 1 m higher than any equipment and of a type approved for lightning protection. All grounds shall be arranged to minimize conduction of atmospheric currents through any cables travelling to Measurand equipment, or through the conduit containing the cables.

 

How long can I expect SAA to last?

In over two years of operation, we have seen no drift over 1.5 mm. We expect the same result after 20 years, based on:

a) the MEMS were designed for airbag deployment in the auto industry. Auto industry specifications require no drift over a 20 year period usually, certainly 10 or 15.

b) Consideration of the materials should give the reasonable observer comfort based on: pure silicon structures, tiny dimensions (microns, sub-mm), hermetic sealing.

c) There is no source of drift in the electronics, most of which are digital. Any analog paths use multiple levels of voltage regulation.

d) All sensors are compensated for temperature changes, using multiple regression and temperature poses, applied through calibration files in the software. Temperature is measured using digital ICs, not cheap and variable thermistors.

e) If water enters the array (only possible through misuse), it will be stopped by bulkheads placed every 2.4 m along the array. It will lead to obvious signal degradation, in which case the array can be repaired on an octet basis (every 8 segments, 2.4 m). In the early stages of water ingress it would be possible for the ingress to masquerade as a soil deformation. We recommend against mis-using the arrays wherever possible.

 

 When do I have to re-calibrate an SAA?

For the reasons above, and from experience with arrays operating continuously in the field for over two years, we expect no requirement for re-calibration of an installed array.

 

An array can be re-calibrated for vertical pose, but this should never be required for field installations. If it is, something is wrong. In some of the software used to track absolute shape rather than shape relative to a starting shape, it is possible to make the starting shape a "virtual" vertical line. This would be the only justifiable re-calibration of the vertical pose, and is often used for convenience in shaker-table research.

 

Between installations, SAA can be re-calibrated for torsional offset at the joints, which can arise from treatment during removal or storage, and lead to some error in azimuth, but not magnitude. This can be done easily by the user in the field.

 

Can I build a long SAA in the field from shorter pieces?

SAAs are built in 8-segment increments. We do not provide pieces of arrays, because  it is difficult to ensure water-tightness in the field. b) heat is required to seal the coverings and it is difficult to prevent damage to the array in the field due to over-heating. It is possible to send an SAA back to Measurand to be lengthened, shortened, or to have a broken portion replaced.

 

How are data stored and retrieved from an SAA?

There are several methods for accessing and storing data on the array. Data retrieval can be as simple as providing power to the array and taking a reading in real time when the array is attached to a PC, to a more sophisticated connection using cellnet modems and solar panels to communicate to Measurand’s location in Canada, from which you can access the data anywhere there is an Internet connection. Once we know where the arrays would be installed, and how often you need the data, we can make a recommendation and provide pricing on this aspect of the installation.   

 

Some customers choose to use Measurand’s data concentrator to store the data locally for each array. The data concentrator activates the array at designated times and stores the data, usually on a daily basis. Customers can select time of capture and duration of capture, along with many other parameters by connecting a PC to the data concentrator. A PC can be attached at any time to the data concentrator to download the data it has stored. Measurand can supply conversion software that will take the raw data stored on the data concentrator, and convert it to a format that Measurand’s SAA3D viewer software can use to display the data.

 

Each array requires its own data concentrator. The more robust installation is known as an Earth Station. It includes a data concentrator, solar panel, cellnet modem, charge regulator, antenna and necessary cables. Multiple arrays can be supported by one cellnet modem.

 

Measurand’s FTP site makes it possible to have the raw data converted and loaded to a password protected server. There is an annual fee for this service. Measurand has tested the cellnet service in Europe, North America and Japan. There is an annual fee for this service which can vary by where the array can be located.

 

Other options exist for communication if the cellular option is not available where the SAA would be installed.

 

How does the cellnet installation work?

Our most common installation for field arrays is the "cellnet" installation, where data are sent at intervals (usually once per day) to our FTP server. Another server processes the data to make it viewable by SAA3D. The customer then uses SAA3D to download the latest data and view it. The DC can be re-configured over the cellnet to collect at different intervals, to average a different number of samples, and about 18 other variables.

 

The DC can store approximately 3 years of shape data if a 32 m array is read about once per day. Normally it sends data every day, so there is no issue of storage running out. Once the memory is full, or at any time, it can be erased by command over the cellnet (the ftp link described above), or it can be allowed to go in a circle, writing over the oldest data.

 Is an SAA able to take readings even if a segment or segments are cut off from the array?

Generally if there is damage, it will affect at least one octet (8 segments). However, if one octet is damaged, then often the  other   octets will continue to function. Sometimes the data from a damaged octet is not important, such as when it is in soil that  is not moving.