An Indicating instrument should be provided with the following torques:
- Deflecting torque
- Controlling torque or restoring torque
- Damping torque
Deflecting torque(Td):
Deflecting torque refers to the force that acts on a moving coil when it is placed in a magnetic field. The Deflecting torque cause the moving system and pointer of the instrument to move from its zero position. This force causes the coil to rotate and is used in a variety of mechanical and electrical devices, including electric motors and galvanometers. The deflecting torque is created due to the interaction between the magnetic field and the current passing through the coil. The amount of torque generated depends on the strength of the magnetic field, the current passing through the coil, and the orientation of the coil in relation to the magnetic field.
In devices such as galvanometers, the deflecting torque is used to measure the strength of an electrical current. As the current flows through the coil, it experiences a force due to the magnetic field, which causes the coil to rotate.
Controlling torque(Tc):
The Controlling torque limits the movement of the pointer and ensures that the magnitude of deflection is unique & is always the same for a given value of the electrical quantity to be measured. Torque control refers to the ability to regulate the rotational force applied by a motor or engine. This is important in many applications, such as robotics, manufacturing, and automotive industries, where precise control of torque is critical. It is also called restoring torque.
To control torque, various methods can be used, including adjusting the current supplied to the motor, varying the voltage applied to the motor, or changing the resistance of the motor. The following two methods can be provided by controlling torque.
- Spring control method
- Gravity control method
Spring control method:
Two phosphor bronze hair springs of spiral shape are attached to the spindle of the moving system of the instrument. One spring is mounted near one end of the spindle( near the pointer) and the second spindle is at the other end. A spring is used to apply a force that counteracts the force being applied to the system. The amount of force applied by the spring can be adjusted by changing its tension or compression.
Spring control is commonly used in various applications, including valves, brakes, and clutches. For example, in a valve, a spring can be used to regulate the flow of a fluid by applying a force that opposes the pressure of the fluid.
The advantages of using spring control include simplicity, reliability, and low cost. However, it may not provide the same level of precision as other methods, such as electronic or hydraulic control.
Gravity control method:
In gravity-controlled instruments, a small weight is attached to the spindle of the moving system. Due to the gravitational pull, a control torque acting in the opposite direction to the deflecting torque is produced whenever the pointer tends to move away from its initial position. Gravity control is a theoretical method of controlling gravity, which is the fundamental force that attracts two bodies toward each other.
Gravity control remains a subject of intense research and speculation in the scientific community, and its potential implications for technology and space exploration are vast. However, the development of practical gravity control methods is still a distant prospect, and further scientific breakthroughs and advancements in technology will be required to make it a reality.
Damping Torque(Tdp):
The Damping torque minimizes the oscillations of the pointer about its final steady state deflection and makes it steady. Damping torque is a torque that is introduced into a mechanical system to reduce oscillations or vibrations. It is commonly used in various applications, including machinery, vehicles, and structures, to improve stability, reduce wear and tear, and prevent damage. The introduction of damping torque can have various effects on the system's behaviour, depending on the damping level, frequency response, and other factors. In some cases, it can improve the system's response to external forces or disturbances, while in others, it can reduce its natural frequency or limit its range of motion.
Overall, damping torque is a useful tool for controlling oscillations and vibrations in mechanical systems, and its proper application can enhance performance, safety, and durability. following are the different methods that can be used to provide the Damping torque.
- Air friction damping
- Fluid friction damping
- Eddy current damping