It is customary to refer to a phase meter as a device of an electrical measuring series, the function of which is to measure the phase angle relative to a pair of electrical oscillations with a constant frequency. For example, using such a device, you can determine the angle showing the phase shift in a three-phase voltage network. This is its main area of application. In this article, we will consider the device and the principle of operation of the phase meter, as well as the rules for using this device.
Content:
- Briefly about the phase meter
- Electrodynamic
- Digital
- User manual
Briefly about the phase meter
When the device is connected to the measurement circuit, it is connected simultaneously to current and voltage circuits. If it is necessary to work with networks that have three voltage phases, then the device is connected simultaneously to all these voltage phases. The current connection is made to the secondary windings of the transformer.
The device uses a simplified connection diagram. Therefore, it will be easy to figure out the purpose of the phase meter yourself. The current connection is carried out in two phases, therefore the third phase is determined based on the addition of the vectors of only a pair of currents (meaning the measured phases). Also, the purpose of the phase meter is to measure the power factor. In simple language, this device is also referred to as a cosine meter.
At the moment, there are two types of phase meters, the scope of which is to determine the power factor. It is a digital and electrodynamic device. Let's consider them in more detail.
Electrodynamic
An electrodynamic phase meter is often referred to as an electromagnetic phase meter. The design of this type of meter is based on a circuit of the simplest type with a ratiometric direction mechanism, which makes it possible to carry out work on measuring the phase shift. This phase meter contains a pair of frames, rigidly connected to each other. There is an acute angle between them equal to 60 degrees. The frames are mounted on axles that are fixed in supports, so there is no mechanical counter-moment in the device.
There are certain conditions that can be set only by shifting the phases of the currents in the circuits of such frames. The movable component of the phase meter is rotated by an angle equal to the angle, which characterizes the phase shift index. A linear scale on the device makes it possible to record the result of the measurement.
Let's consider the principle of operation of an electrodynamic phase meter. In such a device there is a fixed-type coil with a current and a pair of coils in a movable form. Each of the coils of the moving type has its own currents that create magnetic fluxes in the stationary and in the moving coils. Therefore, it can be assumed that the streams of the coils that interact generate a pair of torques. The values of these moments are largely in direct proportion to the location of the pair of coils relative to each other, as well as the angle by which the moving components of the phase meter are rotated. These moments are directed in different directions, opposite to each other. The average values of these moments are dependent on the currents that flow in the moving coils and on the current in the stationary coil. There is also a dependence on the design of the coils and on the phase angle between the coils.
Thus, the mobile component of the phase meter will rotate under the work of these moments until the state of equilibrium will not be obtained, which will be caused by the equality of the moments themselves following the results of the turn. The very same scale of such a device can have a gradation in the system of power factors, which will be convenient for carrying out a number of measurements.
The disadvantage of electrodynamic phase meters is mainly the direct dependence of the readings obtained on the frequency value. In addition, there is also a large power consumption from the source, which is being researched.
Digital
This type of phase meter is manufactured in several ways. For example, a compensation-type phase meter has one of the highest degrees of accuracy, despite the fact that it is performed manually. The principle of operation of the compensation phase meter is completely different. In such a device there is a pair of sinusoidal voltages. In this case, the purpose is to determine precisely the phase shift between them.
Initially, the voltage is applied to the so-called phase shifter controlled by a special code directly from the control device. The phase shift will change gradually until it reaches a state of in-phase. During tuning, the sign of the shift of these phases is determined using a phase-sensitive detector.
The output signal is fed directly from this detector to the control device. The control algorithm is implemented directly by the pulse coding method. After equilibration, the phase shifter input code will show the amount of phase shift. This is its basic principle of operation.
Today, digital phase meters use the principle of discrete counting in their work. This method works in two stages. Initially, there is a process associated with the transformation of the phase shift into an indicator of a signal that has a certain duration. Then the very length of this impulse changes with the help of a discrete counting. This device includes a phase-to-pulse converter, a time selector, a discrete pulse generator, as well as a counter and a control device. It is important to know that digital phase meters have a smaller measurement error, because calculations are carried out at the expense of several periods.
User manual
The best manual explaining how to use the phase meter is its instruction manual, which must be included in the package. Before starting work, you must perform a number of sequential actions. It is important first of all to make sure that the frequency range meets the metrological characteristics, as well as that the external conditions are consistent with the operating conditions. After that, you can already assemble the circuit.
So, the operation of the phase meter should be carried out in the following sequence:
- Initially, you must carefully read the instructions for use attached to the device, where you can learn about its purpose and rules of use.
- With the help of the corrector, the arrow is set at the zero value mark.
- It is necessary to see that all buttons are in the depressed position.
- Connect the input probes to the appropriate connectors.
- Now you need to turn on the network button. At this moment, a special indicator should light up.
- Further, you should not immediately start measuring, since the device needs time to warm up. This procedure will take about a quarter of an hour.
- Now we find the signal voltage from the input side.
- We press one of the buttons depending on the required voltage and set the required frequency range.
- After that we press «> 0
- Channel probes are plugged into the 4-pole input.
- Next, set the switch for the limits to the "20" position.
- After that, the arrow of the meter itself is set using the regulator "> 0
It is much easier to use a digital phaser. The video review below clearly shows the operation of this device:
Now you know how to use a phase meter and what this device is for. We hope the provided material was useful and understandable for you!
You probably don't know:
- Why is phase imbalance in a three-phase network dangerous?
- How to use the phase indicator
- How to distribute the load across phases
