Differential manometer: the principle of operation, types and types. How to choose a differential pressure gauge

Pressure in gaseous and liquid media is one of the most important indicators, the measurement of which is required for the maintenance of communication and technological systems. The working objects include various filters, pipeline systems, air conditioning and ventilation devices. Using a differential manometer, the user not only reveals the characteristics of the operating pressure, but also gets the ability to record the difference between the dynamic values. Knowledge of this data facilitates system monitoring and improves operation reliability. In addition, the dif- manometers are also used to measure the flow of liquid, gas or compressed air.

Principle of operation

In most manometers, the technology for determining and calculating data is based on deformation processes in special measuring blocks, for example, in bellows. This element acts as an indicator that perceives pressure differences. The unit also becomes a differential pressure converter - the user receives information in the form of moving the pointer arrow on the device. In addition, data can be presented in the Pascals, covering the entire measurement spectrum. This way of displaying information, for example, provides a differential pressure gauge Testo 510, which during the measurement eliminates the need to keep it in your hand, as special magnets are provided on the back of the device.

In mechanical devices, the main indicator is the position of the arrow controlled by the lever system. The movement of the pointer occurs until the differences in the system cease to affect a certain force. A classic example of this system is the differential pressure gauge DM 3538M, which provides a proportional transformation of the delta (pressure difference) and provides the result to the operator in the form of a unified signal.

Classification

In view of the complexity of the pressure measurement processes , the characteristics of the working media and the further conversion, there are several variants of differential pressure gauges for operating under different conditions. By the way, the differential manometer, whose operation principle is largely determined by its design, is oriented in its device to the possibility of application in specific environments - hence, classification is made from this. So, manufacturers produce the following models:

• A group of liquid differential pressure gauges, which includes float, bell, tube and ring modifications. In them, the measuring process takes place on the basis of the parameters of the liquid column.
• Digital differential manometers. They are considered to be the most functional, since they make it possible to measure not only the characteristics of pressure drops, but also the velocity of compressed air streams, moisture and temperature parameters. A bright representative of this group is the differential manometer Testo, which is also used in environmental monitoring systems , in aerodynamic and environmental studies.
• Category of mechanical devices. These are bellows and diaphragm versions that provide measurement by monitoring the characteristics of a pressure sensitive element.

Two-pipe models

These instruments are used to measure pressure values and to determine the differences between them. These are devices with a visible level, which is usually represented in a U-shape. By design, this differential manometer is an installation of two vertical communicating tubes, which are fixed on a wooden or metal base. An obligatory component of the device is a plate with a scale. In preparation for the measurement, the pipes are filled with a working medium.

The flow of the measured pressure begins in one of the pipes. Simultaneously, the second tube interacts with the atmosphere. During the measurement of the delta, both tubes undergo a measured pressure. A two-pipe differential pressure gauge with liquid filling is used to measure the vacuum indices, pressure of non-aggressive gases and air media.

Single-pipe models

Single-tube diffanometers are usually used if it is necessary to obtain a result of high accuracy. In such devices, a wide vessel is used, on which the pressure with the greatest coefficient acts. The only tube is fixed to the plate with a scale showing these differences, and communicates with the atmospheric environment. In the process of measuring pressure drops, the smallest of the pressures interact with it. The working medium is poured into the differential pressure gauge until the zero level is reached.

Under the influence of pressure, a certain fraction of the liquid flows into the tube from the vessel. Since the volume of the working medium that has moved to the measuring tube corresponds to the volume that emerged from the vessel, the single-tube differentialometer measures the height of only one liquid column. In other words, the measurement error is reduced . Nevertheless, devices of this type are not spared from shortcomings.

Deviations from optimal values may be due to the temperature expansion in the instrument's measuring components, the density of the working medium, and other errors, which, incidentally, are characteristic of all varieties of the diffusers. For example, a differential digital pressure gauge, even taking into account corrections for density indices and temperature coefficients, also has a certain error threshold.

Membrane Diffmanometers

The main subtype of mechanical differential pressure gauges, which is also divided into devices with metal and nonmetallic measuring elements. In devices with a flat membrane made of metal, calculations are made based on fixing the characteristics of deflections in the measuring component. Distributed and differential pressure gauge, in which the membrane acts as a dividing wall for the chambers. At the moment of deformation, the counteracting force is formed by a cylindrical spiral spring unloading the measuring element. This is how the two different pressure values are compared.

Also, some modifications of the membrane devices are provided with protection from unilateral action - this feature of the design allows them to be used in the measurement of overpressure indicators . Despite the active introduction of electronics into the metrological branch as a whole, membrane measurement instruments remain in demand and even indispensable in some areas. For example, the high-tech differential DMC-01m digital type manometer, despite its ergonomics and high accuracy, has a number of limitations for use in environments where membrane devices can be used.

Bellows versions

In such models, the measuring element is a corrugated metal box, supplemented by a spiral spring. The plane of the device is divided by the bellows into two parts. The greatest effect of pressure falls on the chamber outside the bellows, and the smallest - in the inner cavity. As a result of the effect of pressures with different forces, the sensing element is deformed in accordance with a value proportional to the desired index. These are classical differential pressure gauges, showing the results of measurements by an arrow on the dial. But there are other representatives of this family.

Other mechanical versions

Circular, float and bell devices for measuring the difference in pressure are less common. Although among them there are relatively accurate non-recessive and self-recording models, as well as devices with contact electrical devices. Data transmission in them is provided remotely again, by means of electrical communication or pneumatics. To determine the expenditure indicators on the basis of variable differences, mechanical devices with summing and integrating additions are also produced.

Digital Differential Meters

Devices of this type, in addition to the basic functions of measuring the difference in pressure, are able to determine the dynamic characteristics of working media. Such devices are marked DMC-01m. Differential pressure gauges, in particular, are used in ventilation systems for production facilities, it is possible to calculate gas consumption figures, taking into account temperature corrections, and also to record average costs for measured items. The device is equipped with a microprocessor, which automatically keeps records of measurements and the accumulation of information on the flue. All received information about the results of work is displayed on the display.

Recommendations for selection

Calculation operations with pressure indicators require the use of a reliable device that best meets the operating conditions. In this regard, it is important to determine the list of functions that the device will perform. For example, the differential pressure gauge Testo 510 is able to provide accurate readings with temperature compensation and provide data on a digital display. In some cases, a signaling model is required, so you should consider the availability of this option.

For the most correct data in advance, you need to compare the characteristics of the device with the ability to operate in a specific working environment. Not all devices can be used in oxygen, ammonia and freon environments. At least, their accuracy can be low.