Bonded wire strain gauges are used on the surfaces of different structures. This is the reason why they are referred to as bonded gauges. There are three types of bonded wire strain gauges. The first type is referred to as fine wire strain gauge, the second type is known as metal foil wire strain gauge while the third one is known as semi-conductor bonded wire strain gauge (Bonded Strain Gauges 3).
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The arrangement of fine bonded wire strain gauge is comprised of various parts. The first part is a wire of fine resistance which bends repeatedly to attain a diameter of 0.025 mm. The bending is aimed at increasing the wire length to make it possible for stress to be uniformly distributed.
The position of the resistance wire is between Teflon, Bakelite or paper which constitutes the carrier base. The function of the carrier base is to shield the gauge from getting damaged (Bonded Strain Gauges 2).
Fine bonded wire strain gauge has several advantages as compared to other types of bonded wire strain gauges. The first advantage is that it is highly accurate. The second advantage is that it has a linearity of +/- 1 percent while the third advantage is that it has a range of +/- 0.3 percent of strain.
However, it still has some limitations. The first limitation is that due to the fact that the gauge has a bond with the structure, it is restricted from detaching itself thus it is difficult to use it again. The second limitation is that it is an expensive gauge to acquire (Bonded Strain Gauges 3).
The second type of bonded wire strain gauge is the metal foil bonded wire strain gauge. It has an arrangement comprised of a metal foil whose thickness is 0.02 mm. Printed circuit technique is the method used to produce the metal foil. The foil is combined with lead through soldering in order to establish an electrical connection between a measuring device and the strain gauge.
The first advantage of this type of bonded wire strain gauge is that it can be produced in different shapes. The second advantage is that the gauge is characterized by an improved fatigue life while the third advantage is that it is highly sensitive and it remains stable even when temperatures are high. The fourth advantage is that peeling off of the backing is possible (Sharpe 282).
The third type of bonded wire strain gauge is referred to as piezo restive or semi-conductor strain gauge. This gauge is made up of a rectangular shaped element for sensing. After its manufacture, another process known as doping is carried out. The element for sensing is then placed on a backing made of stainless steel or plastic.
In order to link the strain gauge with a measuring device in an electric manner, gold leads are extracted from the element used in sensing. N-type which is also referred to as the negative and p-type commonly known as the positive are the two elements of sensing which are widely used.
In the negative type, there is a decrease in resistance in relation to tensile strain while in the positive one, an increase in resistance in relation to tensile strain is recorded.
This type of gauge has several advantages. The first advantage is that it has a huge gauge factor which makes it possible for minute strains to be determined. The second advantage is that it has satisfactory response frequency. The third advantage is that it has a sustainable fatigue life while the fourth one is that it has 2.3 per cent accuracy. However, this type of gauge has a number of limitations.
The first limitation is that it is brittle, a factor that prevents it from taking measurements of huge strains. The second limitation is that it does not have a constant gauge factor while the third limitation is that it has poor linearity. In addition, the gauge is also expensive to acquire (Bonded Strain Gauges 5).
Bonded Strain Gauges 2011. Web. <http://instrumentationandcontrollers.blogspot.com/2010/11/bonded-strain-gauges.html>.
Sharpe, William. Springer Handbook of Experimental Solid Mechanics. New York: Springer, 2009. Print.