Selecting the Right Moisture Meter
Here at Test Equipment we supply a range of moisture meters, which are used extensively in a wide range of industries to undertake accurate moisture content measurements in various materials. One of the reasons for deciding to write this article was because across these industries, the capabilities of different moisture meters and the way in which they work is very misunderstood on the whole. What one moisture meter is suitable for, another one may not be, and although all moisture meters do the same thing - measure moisture content, the way that they do it and display the results is very different indeed.
The main, and most obvious difference is pin and pinless technology. Some meters use pins, which the user nees to push into the material being measured to obtain a reading. The pinless meters are non-destructive and do not leave any marks behind, and are therefore more widely used today than the moisture meters which use pins. Some years ago, we supplied far more moisture meters using pins than we do today. In recent years there has been a shift away from the pin type moisture meters, to the pinless ones as the technology and accuracy improves. The pin meters work in a very simple manner - they measure moisture by passing a small electrical current across the pins and through the material being measured. The conductivity of the material influences the passage of this current (the resistance changes) and you get a moisure reading in percent. With the pinless moisture meters, they too pass an electric field into the material and measure it, but this time the field extends into the material to a depth of typically 20mm to 50mm and as a result the moisture content is measured not between two pins, but in a cross sectional area of the material. The reading obtained is also 0-100 but this is not always a moisture content by percentage, but represents the moisture meter's dynamic scale (in other words 0 is the lowest end of the scale that the moisture meter can read and 100 is the top of it's scale).
Pin or Pinless Moisture Meter Technology ?
Because the pin type moisture meter is easier and simple, it still has a dedicated following, but there are limitations. For instance, they are not easy to use with certain materials, such as concrete as it is too hard and means drilling holes for the pins to be correctly inserted. The other thing is that the moisture content is more of a surface reading (between the tow pins). Finally, the last drawback is the pin holes that are left behind, which may be OK for some applictions, such as measuring timber or certain types of building materials, but if measuring a nice polished wooden floor or a nicely decorated house, it may have re-percussions.
The pinless meters also have their bad points as well as their good points. For example, a pinless moisture meter uses what is known as a relative or comparative method. This requires that the user places if somewhere dry and sets it to a reference point, or sets it to zero. As it is moved across the surface of something, the reading changes relative to the zero reading. This is not a moisture content in percent but a reading as a percentage of the meters maximum scale. However some of the better featured moisture meters have scales loaded into them, so that they can measure by pinless technology and still give the reading as a percentage content by weight in certain materials.
For example the VI-D4 can measure concrete, cement, and anhydrite screed moisture by percent. The VI-D6 can measure moisture content by weight in percent in concrete and a huge range of timbers. The GM-200 which is the most popular moisture meter in our product line up can measure percent by weigh in hardwood, softwood, gypsum (plasterboard), concrete and various other building materials. However what has to be understood here is that ALL of these meters can measure ANY material in relative mode, which is perfect for applications where the user needs to know if something has moisture or not, rather than requiring an exact moisture content by percentage weight.
The latest technolgoy in pinless moisture meters, the FLIR MR160 even has infrared guidance built into it, which uses a very basic thermal image to guide the user to areas of moisture content. That meter would require a whole new discussion, so the link to it is right here.