Strain Gauge Rosettes | Resistances Heating | Indirect resistance Heating

Here we learn about Strain Gauge Rosettes with diagram

Strain Gauge Rosettes

~ Multiple grid or rosettes are a group of gauges bonded to the same supporting material in definite relative
positions.

~ When two 0r more grid elements are configured in a definite fashion for use at one point, then it is called a strain gauge rosette. In the use of a single element gauges, the orientation is a critical factor and are

useful only in known directions.
~ But, with the use of strain gauge rosettes, there is no restriction on the orientation and can be used to measure stress whose magnitude and direction are totally unknown.

~ Theoretically, it is possible  calculate all the desired information when a 3-gauge rosette is used for measurement at a point. The different types of strain gauge rosettes are shown in Fig. 5.6.7.
~ Depending upon the arrangement of the grids, we have the rectangular, delta and T delta rosettes.

Resistances Heating

~ When a resistance R carries a current I for t seconds, I" R t is the heat produced.
~ This heat is used for heating purposes.
~ There are two types of resistance heating, direct heating and indirect heating.

Direct Resistance Heating:

~ Usually, the body to be heated is called a charge. In the process of direct heating an electric current is passed through the charge itself.
~ If R is the resistance of the charge, I" R t is the heat produced.
~ As the heat is developed in the charge itself, this becomes a very efficient process of heating.
~ Water heater is a well known example of this type.
~ The immersion type water heater is shown in Fig. 11.3.1.
Fig..
~ The direct resistance heating has a high efficiency because the heat is produced in the charge itself.

Indirect resistance Heating :

~ Here a wire of nichrome, canthi (or some similar alloy) acts as a heating element.
~ If R is the wire resistance carrying current I, then I" R t is the heat generated.
~ This heat is transferred to the charge by conduction, convection or radiation.
~ Most of the resistance ovens work as indirect heaters where heat is transferred by radiation.
~ An electric iron as an example of indirect resistance heating where the heating element is in almost direct contact with the iron body and therefore the iron receives heat by conduction.
~ In case of electrical water boilers, or immersion heaters, heating element is immersed in water itself and heat is transferred to water by convection.
~ Room heaters, baking ovens, etc. are heaters where heat is transferred by radiation, resistance ovens are used for different purposes such as annealing and hardening of metals, drying and baking of pottery, staving of enameled ware, domestic cooking, etc.
~ In all these cases heat is radiated to the charge.

Aplications of indirect reslstance heating:

1. Cooking ovens
2. Water geyser
3. Room heaters
4. Furnaces
5. Pottery work
6. Heat treatment of metals