1.3. Classification of pressure measuring instruments and their main technical characteristics

Strain gauge transducers

The principle of operation of strain gauge transducers is based on the dependence of the electrical resistance of the metal. Strain gauges are placed on the elastic sensing element of the pressure gauge. The change in their resistance is converted into an electrical signal and transmitted to secondary devices. To measure high and ultra-high pressures in laboratory practice, deadweight pressure gauges are used. You can purchase industrial equipment in the online store "Industrial Automation"

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Types and work

Devices for measuring pressure are called pressure gauges. In technology, it is most often necessary to determine excess pressure. A significant range of measured pressure values ​​and special conditions for measuring them in various technological processes determine the variety of types of pressure gauges, which have their own differences in design features and operating principles.

Types of pressure

• Atmospheric pressure is generated by the Earth's atmosphere.
• Vacuum pressure is pressure that does not reach atmospheric pressure.
• Excess pressure is a pressure value that exceeds atmospheric pressure.
• Absolute pressure is determined from the value of absolute zero (vacuum).

Electronic models

Electronic blood pressure monitors operate using the oscillometric method. In their case, the use of a stethoscope is not required, the total numbers will be automatically shown on the screen. Measuring pressure with an electronic tonometer is extremely convenient for people with poor hearing and vision. One of the advantages is the ability to determine the number of heartbeats and the presence of arrhythmia. The results obtained can be saved in the device memory. Unlike a mechanical tonometer, even a child can use an electronic device, since measuring blood pressure is very simple and sometimes just pressing 1-2 buttons is enough.

An electronic tonometer can be automatic or semi-automatic. In the first case, it is enough to put on the cuff and press the button to start determining blood pressure. Semi-automatic blood pressure monitors are cheaper, but you have to pump the air manually. After reaching the required pressure, the device itself releases air.

The following algorithm will help you understand how to correctly measure pressure using semi-automatic tonometers:

• fix the cuff 3 cm from the elbow;
• pump air until the device is tightly connected and stop;
• look at the final result shown on the display.

With an automatic tonometer, the procedure is even easier. How to measure pressure correctly can be seen below:

• Fix the cuff and press the button located on the display.
• After completing the operation of the device, look at the display to familiarize yourself with the result.

Liquid pressure gauges

The operating principle of liquid pressure gauges is simple. The pressure in them is measured by the height of the liquid in the column. The design of such devices consists of two communicating vessels with a working fluid. One end of the vessel is connected to the medium whose pressure needs to be measured, the other end remains open. Pressure affects the liquid in the vessel and it begins to move from one elbow to another. The fluid difference will be proportional to the excess pressure. Also, using a liquid pressure gauge, you can measure vacuum and pressure difference. But such a device cannot measure pulsating pressure.

Instructions for using a mechanical tonometer

The instructions below will help anyone understand how to measure pressure with a mechanical tonometer:

• The person should sit on a chair with his back and legs straight. Next, you need to place your hand on the table, on which the pressure will be measured with a tonometer. If a person is right-handed, then it is better to carry out the procedure on the left limb, and vice versa. For a more accurate result, doctors advise taking measurements on both hands in turn.
• A cuff is placed on the arm 3 cm from the elbow bend and secured with Velcro.
• The stethoscope membrane is applied to the bend of the elbow.
• With the help of a bulb, air is supplied to the cuff. You need to stop pumping it 30 units after the last pulse beat heard.
• After reaching the required point, you need to turn the wheel a little under the pear. Air should come out no faster than 2 units per second. The first beat heard will be the upper pressure reading, and the last one will be the lower one.

This algorithm of actions represents the auscultatory measurement technique invented by N. S. Korotkov at the beginning of the twentieth century. In the absence of a stethoscope, the question of how to measure blood pressure becomes more pressing. The palpation method for determining values ​​can help here. The technique will generally be identical to the auscultatory type, but in this case, instead of a stethoscope, the index and middle finger are used. The measurement accuracy does not change and the palpation method is well suited for people who have hearing problems.

There are certain rules by following which you can learn how to measure blood pressure correctly. Their list is as follows:

• Before measuring the baby’s blood pressure, he needs to be told about this procedure and asked to wait a couple of minutes. Usually this method helps, but in the case of children it is better to use automatic blood pressure monitors, as they show the result faster.
• Even the most modern blood pressure monitors will not show accurate numbers if a person is cold or hot. In one case, the vessels narrow and the pressure rises, and in the other they expand and it drops.
• Before measuring your blood pressure, it is advisable to rest for half an hour to calm down and relax.

Strain gauges

Such pressure gauges operate on the principle of deformation of the measuring element. A spring, membrane or bellows can be used as an elastic element. Spring devices contain an oval tube, which is bent around a circle and connected through a special mechanism to an arrow. Diaphragm pressure gauges use a special membrane as the main element. The pressure bends the membrane and information about this is transmitted through the transmission mechanism to the pointer. A bellows pressure gauge, as the name suggests, is equipped with a bellows - a corrugated tube into which pressure is applied. Under pressure, the bellows stretches and information about this is sent to the arrow. Diaphragm and bellows devices are often used to measure low pressures. Electrical modifications of deformation pressure gauges make it possible to record and remotely transmit data.

Operating principle of the device

A device for measuring blood pressure, regardless of whether it is mechanical or automatic, works according to one principle, namely:

• The cuff is put on.
• Air is pumped into it to compress the artery.
• The air is gradually removed from the cuff and the first pulse beat is recorded, which is the upper blood pressure (systolic).
• The last beat shows the lower (diastolic) blood pressure.

The value between the upper and lower readings is the pulse pressure. All modern semi-automatic, automatic and mechanical tonometers operate on this principle.

Sometimes the tonometer shows different pressure on the right and left arm. If the difference does not exceed 15 units, then there is usually nothing to worry about, but when it is greater than this indicator, then you need to be examined.

Differences in pressure can be caused by malfunctions of internal organs, VSD, diseases of the cardiovascular system, as well as simple stress and overwork. A slight increase in indicators on the left hand, especially if the person is left-handed, is allowed due to the nutrition of this limb by the aorta itself.

To understand how to correctly measure pressure yourself, you need to become more familiar with the features of the selected device. It is equally important to learn the rules that must be followed to obtain accurate data.

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