What Are the Different Types of Strength Dynamometer?

The DC power dynamometer adopts a double-excitation DC motor. The external excitation can expand the speed adjustment range of the dynamometer. When the inverted drag machine is used as a motor, a series winding with the same magnetic field direction and the externally excited magnetic field can be used to make the dynamometer have a large torque at low speeds, which is very necessary for the startup of power machinery.

DC power

When the output shaft of the power machine under test is connected with the rotor of the DC electric dynamometer to rotate, the armature winding cuts the magnetic field lines of the stator winding magnetic field and generates induced electromotive force in the armature winding, that is, a system opposite to the direction of rotation Dynamic torque, at this time, the motor operates as a generator to achieve the purpose of measuring power as a load. On the contrary, when an armature circuit has a current passing through it, it will be subjected to electromagnetic force in the magnetic field to generate a driving torque in the same direction as the rotation direction. At this time, the motor operates as a motor and is used to drag the power machinery to rotate.

Whether it is used as a generator for power measurement or as a motor for dragging, when the stator is subjected to the rotor torque through a magnetic field, it is also subjected to a counter torque of the same magnitude and opposite direction. This torque can be measured by the force measurement mechanism. found out. Since the swing direction of the dynamometer changes with the use of the dynamometer and the rotation direction of the rotor, the force acting on the dynamometer mechanism can only be allowed to act in one direction, so the force arm and the dynamometer mechanism generally pass through Four-bar linkage is connected. A ring-shaped tension pressure sensor is widely used as a force measurement mechanism, and this force measurement mechanism can be directly connected to the force arm of a dynamometer.

There are two types of control methods for DC electric dynamometers: load resistance control and automatic feeding network control. The characteristics of DC electric dynamometers are related to the control methods. They must be based on the experimental purpose and test methods of power machinery, as well as power and economic aspects. A variety of factors are considered comprehensively, and the control method of the dynamometer is selected. ^[1]

The characteristic curve of the DC power dynamometer is shown in Figure 2. A: The working range of the DC power dynamometer is determined by the characteristics of the DC motor. Corresponds to the maximum excitation current and the minimum load resistance. B: Maximum torque line, limited by the mechanical strength of the armature C: Because the allowable temperature rise and insulation voltage of the motor have certain restrictions, if the temperature rise is constant, the current I through the armature winding must not exceed a certain maximum Value D: Mechanical strength E: No-load line ^[2]

The DC electric dynamometer is composed of a DC balancing machine, a converter unit, an excitation unit, and a load resistance, which are relatively complicated. The magnetic field of the DC balancing machine adopts complex excitation, that is, self-excitation and other excitation. Its stator magnetic field is generated by its own DC and externally supplied DC power. This way of generating excitation can expand the adjustment range of the dynamometer.

The converter unit is also called a generator set. It consists of a three-phase asynchronous motor and a DC motor. It has two working states:

When the internal combustion engine is working, the DC balance motor is driven. At this time, the DC balance motor is used as a generator. The DC balance motor DC motor three-phase asynchronous motor power grid.

Drag the DC balance motor of the internal combustion engine as the motor. The power grid three-phase asynchronous motor DC motor DC balance motor DC balance motor of the internal combustion engine and the DC motor of the converter unit need DC excitation source. Excitation DC power is supplied by the excitation unit. ^[2]