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Moisture Meters- The Key Facts

August 9th, 2010 Comments off

Moisture Meters- The Key Facts

The measurement and detection of moisture and the meters used is a complex and important topic that is frequently misunderstood.

This article will outline the differences between the concepts of  ‘moisture measurement’ and ‘moisture detection’ as well as explain the most appropriate type of meter to use in different situations.

Moisture Measurement In Timber

The most common material in which moisture content can be ‘measured’ by using a moisture meter is timber. The typical tool used for this purpose is the widely available pin type meter (also known as an electrical resistance/conductance and destructive meter).

These instruments work by reading across the two pins and detecting the change in resistance when they come into contact with the timber.Pin meters will give a pretty good indication of the moisture content of timber. They are made and calibrated to do this on particular species of timber for example, Douglas Fir. These instruments work because the conductivity of timber (also known as the density), is reasonably constant throughout different timber types and is proportional to the moisture content. As there are timbers which have different densities to that which the instrument has been calibrated to, most meters are supplied with a set of tables which give the adjustments which need to be made dependant upon the type of timber being tested.

Limitations Of Pin Meters For Building Surveys

As described above, the common pin meter has been designed for use on timber and not any other materials. This fact is often not appreciated by many users who rely on pin meters to ‘measure’ moisture content in other materials such as masonry, plaster or wallpaper. This is not actually possible as there are major variations in, for example masonry and therefore no consistency between any two samples from different sites. The same holds for most common building materials.

All a pin type meter can indicate, at best, is whether moisture may be present but they can not measure the actual level of moisture in the material. The danger of using a pin meter is that the instrument only reads across the very small area between the pins. This is not such a problem with timber due to the homogenous nature of it. However, when looking for moisture in an internal wall, it would be necessary to make many pin holes all over the wall in order to get a thorough indication of whether there is a presence of moisture. This is time consuming and leaves behind unsightly holes. When faced with tiled areas (such as kitchens & bathrooms) the pin meter can not be pushed through tiles and as a result no readings can be taken or at best only a surface reading is obtained. The presence of certain substances on the surface of the material being tested, such as condensation and salts, will also affect the readings.

Thank-you to Mobile CAD Surveying for allowing us to copy this from their site.

For more information of a similar nature to this above, pelase visit the Mobile CAD Surveying Knowledge Base

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Surveying & Triangulation

August 5th, 2010 Comments off

Surveying & Triangulation

If you are going into the surveying industry then you need to know what survey equipment you will need. We have every type of surveying equipment that you can think of. We sell our survey equipment at unbelievably low prices; we always have specials so make sure to check back often.

Surveying Equipment

When looking for surveying equipment there are a lot of different things you need to take into consideration. What kind of surveying are you going to be doing, do you want to use a total system or would you rather use a theodolite, and how much can you afford to spend on your surveying equipment. The surveying equipment that we sell is the highest quality surveying equipment around.

The History Of Surveying And Survey Equipment

Surveying is the technique and science of accurately determining the terrestrial or 3D space position of points and the distances and angles between them. These points are usually, but not exclusively, associated with positions on the surface of the Earth, and are often used to establish land maps and boundaries for ownership or governmental purposes. In order to accomplish their objective, surveyors use elements of geometry (Latin: measuring the Earth), of engineering, mathematics, physics, and law.

Surveying has been an essential element in the development of the human environment since the beginning of recorded history (ca. 5000 years ago) and it is a requirement in the planning and execution of nearly every form of construction. Its most familiar modern uses are in the fields of transport, building and construction, communications, mapping, and the definition of legal boundaries for land ownership.

Historically, angles and distances were measured using a variety of means, such as chains with links of a known length, for instance a Gunter’s Chain (see Edmund Gunter), or measuring tapes made of steel or invar. In order to measure horizontal distances, these chains or tapes would be pulled taut, to reduce sagging and slack. Additionally, attempts to hold the measuring instrument level would be made. In instances of measuring up a slope, the surveyor might have to “break” the measurement that is, raise the rear part of the tape upward, plumb from where the last measurement ended.

Historically, horizontal angles were historically measured using compasses, which would provide a magnetic bearing, from which deflections could be measured. This type of instrument was later improved upon, through more carefully scribed discs, providing better angular resolution, as well as through mounting telescopes with reticles for more precise sighting atop the disc (see theodolite). Additionally, levels and calibrated circles allowing measurement of vertical angles were added, along with verniers for measurement down to a fraction of a degree such as a turn-of-the-century Transit (surveying).

The simplest method for measuring height is with an altimeter (basically a barometer) using air pressure as an indication of height. But for surveying more precision is needed. Toward this end, a variety of means, such as precise levels have been developed, which are calibrated to provide a precise plane from which differentials in height between the instrument and the point in question, typically through the use of a vertical measuring rod.

The basic tool is a theodolite, set on a tripod, with which one can measure angles (horizontal and vertical), combined with triangulation. Starting from a benchmark, a position with known location and elevation, the distance and angles to the unknown point are measured. A more modern instrument is a total station, which is basically a theodolite with an electronic distance measurement device (EDM). Still more modern is the use of satellite positioning systems, such as a Global Positioning System (GPS). Though GPS systems have increased the speed of surveying, they are still only accurate to about 20 mm. As well GPS systems do not work in areas with dense tree cover. It is because of this that EDMs have not been completely phased out. Robotics allows surveyors to gather precise measurements without extra workers to look through and turn the telescope or record data. A faster way to measure (no obstacles) is with a helicopter with laser echolocation, combined with GPS to determine the height of the helicopter. To increase precision, beacons are placed on the ground (about 20 km apart). This method reaches a precision of about 5 cm.

With the triangulation method, first, one needs to know the horizontal distance to the object. If this is not known or cannot be measured directly, it is determined as explained in the triangulation article. Then the height of an object can be determined by measuring the angle between the horizontal plane and the line through that point at a known distance and the top of the object. In order to determine the height of a mountain, one should do this from sea level (the plane of reference), but here the distances can be too great and the mountain may not be visible. So it is done in steps, first determining the position of one point, then moving to that point and doing a relative measurement, and so on until the mountaintop is reached.

Triangulation

In trigonometry and elementary geometry, triangulation is the process of finding a distance to a point by calculating the length of one side of a triangle, given measurements of angles and sides of the triangle formed by that point and two other reference points.

Some identities often used (valid only in flat or euclidean geometry):  The sum of the angles of a triangle is pi rad or 180 degrees. The law of sines – The law of cosines – The Pythagorean theorem Triangulation is used for many purposes, including surveying, navigation, metrology, astrometry, binocular vision and gun direction of weapons.

Many of these surveying problems involve the solution of large meshes of triangles, with hundreds or even thousands of observations. Complex triangulation problems involving real-world observations with errors require the solution of large systems of simultaneous equations to generate solutions.

Thank-you to Mobile CAD Surveying for allowing us to copy this from their site.

For more information of a similar nature to this above, pelase visit the Mobile CAD Surveying Knowledge Base

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The Mobile CAD Surveying Knowledge Base

July 14th, 2009 Comments off

Mobile CAD Surveyings Knowledge Base

Mobile CAD Surveyings Knowledge Base

Mobile CAD Surveying Knowledge Base

The Mobile CAD Surveying Ltd Knowledge Base is produced for customers and the general public who wish to learn more about surveying, surveying equipment and procedures. The Knowledge Base is regularly updated with useful and factual information by Mobile CAD Surveying staff in direct response to customer enquiries.

If you have a question and can’t find the answer here or would like to contribute to the Knowledge Base please email them sales@mobilecadsurveying.co.uk with your enquiries.

Surveying & Triangulation

Moisture Meters – The Key Facts

What is a Dumpy or Automatic Level and a Laser Level

What is GPS & Glonass

What is RTK

What is a Theodolite

Gradient Reference Chart

Laser Measures v’s Ultra Sonic Measures

Which Leica Disto Do I Require

Leica Disto FAQs

IP Ratings Explained

There are more facts being added all the time, so check back often

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