Dynamometer | Eddy current dynamometer | Strain gauge transmission dynamometer | Advantages and Disadvantages |

By | February 4, 2019

Dynamometer | Eddy current dynamometer | Strain gauge transmission dynamometer | Advantages and Disadvantages | Limitations and diagram.

Dynamometer :

A) Eddy Current Dynamometer :

1) Eddy current is the type of absorption type dynamometer.
2) It consists of non-magnetic solid metallic rotor, which moves to the magnetic field of stator
The stator winding is excited by a D. C. supply as shown in Fig.

Dynamometer

Dynamometer

Fig. Eddy current dynamometer.

3) When the solid rotor moves in the field produced by stator windings an emf is produced in it resulting in a large loss of power due to eddy current.
4) This power is dissipated as heat in the rotor and therefore water is circulated through air gap between stator and rotor.
5) Torque on the stator casing may be measured in the usual manner.
6) Following are the few advantages and limitations :

A) Advantages of Eddy current dynamometer :

1) They are small in size, as compare to any other of the same capacity.
2) The absorption power can be changed by changing d. c. circuit.
3) It can measure high power output at all speeds.
4) Torque developed is smooth and continuous under all operating conditions.
5) The power range of eddy current brake is up to 300 h.p. and maximum speed is 6000 rpm.

B) Limitations / Disadvantages of Eddy current dynamometer :

1) It cannot produce any torque at zero speed.
2) It produces only small torques at low speed.

B) Strain gauge transmission dynamometer :

1) This is also inline rotating torque sensor, which measures torque.
2) Fig. 5.4.3 shows the arrangement of strain gauge dynamometer.

Fig. a) Strain gauge | b Equivalent circuit

Construction and measurement of strain gauge transmission dynamometer :

1) It consists of metal shaft fitted with bonded strain gauge.
2) Here strain gauges are fitted at 45o to shaft axis as shown in Fig. (a).

3) In this type of arrangement 2 strain gauges are subjected to tensile stress and while other is subjected to compressive stress.
4) Strain gauge 1 and 3 must be diametrically opposite to strain gauge 2 and 4.
5) Due to torsion, strain gauge senses compressive as well as tensile deformation.
6) Further these strain gauges are connected to the output of Wheatstone circuit.
7) The output of Wheatstone bridge is proportional to torsion and hence to applied torque on shaft.
8) The bridge power and output of bridge is connected to the sensor through slip ring and brushee as shown in Fig. (b).
9) Following are the few advantages of strain gauge dynamometer.

Advantages of strain gauge transmission dynamometer :

(1) It is sensitive to torque.
(2) It has full temperature compensation.
(3) It provides automatic compensation for bending axial loads.
(4) It gives an instantaneous result.

Disadvantages / limitations of strain gauge transmission dynamometer :

(1) The slip rings may wear out and causes maintenance problem.
(2) The device is generally expensive.
(3) Initial settings need skill and is time consuming,

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