Dynamometer

The wattmeter is an electrodynamic instrument for bar the electric power or the supply rate of galvanizing energy of either given electrical circuit. The device consists of a pair of fixed hand-builds, known as actual scrolls, and a movable coil known as the authorization coil. The current coils are touch baseed in serial with the circuit, while the potential coil is connected in parallel. Also, on analog wattmeters, the potential coil carries a beset that moves over a scale to indicate the measurement.A current f imprinting through the current coil generates an electromagnetic reach around the coil. The strength of this field is proportionate to the line current and in phase with it. The potential coil has, as a general rule, a high-value resistor connected in series with it to reduce the current that flows through it. The result of this ar scarperment is that on a dc circuit, the deflection of the needle is proportional to both the current and the voltage, thus conform ist to the equation W=VA or P=EI.On an ac circuit the deflection is proportional to the average instantaneous product of voltage and current, thus measuring true power, and possibly (depending on load characteristics) showing a different reading to that obtained by simply multiplying the readings showing on a stand-alone voltmeter and a stand-alone ammeter in the same circuit. The two circuits of a wattmeter are likely to be damaged by excessive current.The ammeter and voltmeter are both vulnerable to heat up in case of an overload, their pointers will be driven off scale but in the wattmeter, either or even both the current and potential circuits understructure overheat without the pointer approaching the end of the scale This is because the position of the pointer depends on the power factor, voltage and current. Thus, a circuit with a low power factor will give a low reading on the wattmeter, even when both of its circuits are loaded to the maximum safety limit.Therefore, a w attmeter is rated not only in watts, but also in volts and amperes. Retrieved from http//en. wikipedia. org/wiki/Wattmeter (A dynamometer consists of an concentration (or absorber/driver) unit, and usually includes a means for measuring torque and rotational speed. An absorption unit consists of some type of rotor in a ho using. The rotor is coupled to the engine or other equipment under test and is free to slip at whatever speed is required for the test.Some means is provided to develop a braking torque between dynamometers rotor and housing. The means for developing torque fuck be frictional, hydraulic, electromagnetic etc. according to the type of absorption/driver unit. One means for measuring torque is to mount the dynamometer housing so that is free to turn except that it is restrained by a torque arm. The housing can be made free to rotate by using trunnions connected to each end of the housing to support the dyno in pedestal mounted trunnion bearings.The torque arm is con nected to the dyno housing and a weighing scales is positioned so that it measures the force exerted by the dyno housing in attempting to rotate. The torque is the force indicated by the scales multiplied by the length of the torque arm measured from the center of the dynamometer. A load cell transducer can be substituted for the scales in order to provide an electrical signal that is proportional to torque. Another means for measuring torque is to connect the engine to the dynamometer through a torque sensing coupling or torque transducer.A torque transducer provides an electrical signal that is proportional to torque. With electrical absorption units, it is possible to determine torque by measuring the current drawn (or generated) by the absorber/driver. This is generally a less accurate method, but it may be adequate for some purposes. A wide variety of tachometers are available for measuring speed. Some types can provide an electrical signal that is proportional to speed. When torque and speed signals are available, test data can be transmitted to a data acquisition system rather than being save manually.Speed and torque signals can also be recorded by a chart recorder or plotter. ) Power in an electric circuit is the product (multiplication) of voltage and current, so any meter designed to measure power must account for both of these variables. A special meter deed designed especially for power measurement is called the dynamometer movement, and is similar to a DArsonval or Weston movement in that a lightweight coil of wire is committed to the pointer mechanism.However, unlike the DArsonval or Weston movement, another (stationary) coil is used instead of a permanent magnet to provide the magnetic field for the moving coil to react against. The moving coil is generally energized by the voltage in the circuit, while the stationary coil is generally energized by the current in the circuit. A dynamometer movement connected in a circuit looks something like this pic The top (horizontal) coil of wire measures load current while the bottom (vertical) coil measures load voltage.Just like the lightweight moving coils of voltmeter movements, the (moving) voltage coil of a dynamometer is typically connected in series with a range resistor so that full load voltage is not applied to it. Likewise, the (stationary) current coil of a dynamometer may have precision shift resistors to divide the load current around it. With custom-built dynamometer movements, shunt resistors are less likely to be needed because the stationary coil can be constructed with as heavy of wire as needed without impacting meter response, unlike the moving coil which must be constructed of lightweight wire for tokenish inertia.