Types of pressure sensors

Checking the serviceability of the pressure sensor

If the oil indicator lights up or begins to flicker, you need to check the pressure sensor; it is often the cause of the problem.
The sensor must be carefully inspected; if there are grease leaks around it, most likely the membrane is damaged; accordingly, the rod does not open the indicator circuit, and it continues to burn or flicker. Then it is unscrewed with a key and thoroughly cleaned.

Video: How to check the emergency oil pressure sensor

For diagnostics, you will need a regular pump and a multimeter set to ohmmeter mode. The sensor fitting must be connected to the pump, its terminal to the positive of the ohmmeter, and the negative terminal to be short-circuited to the housing. In this case, the device should show some electrical resistance.

Afterwards, several strokes of the pump are required, and the ohmmeter should show an open circuit, that is, the resistance should reach infinity. In this case, the sensor is working; if not, it requires replacement. After installing the new sensor, the engine starts and the indication disappears. If it remains, you need to look for the reasons for the motor malfunction.

It is more difficult to diagnose the condition of the control sensor, since it is difficult to regulate the pressure readings with the pump. To do this, a special insert for two outputs is installed in the mount under the sensor. The sensor itself and an analog pressure gauge, specially verified, are inserted into them. After starting the engine, compare the readings of these two devices and draw a conclusion about the serviceability of the device.

Seal

Piezoelectric sensors

The piezoelectric element is the basis of the device design. When deformation occurs, the piezoelectric element begins to generate a certain signal. The element is installed in the medium whose pressure needs to be measured. During operation, the current in the circuit will be directly proportional to the change in pressure.

Such devices have one feature - they do not allow monitoring pressure if it is constant. Therefore, it is used exclusively in cases where the pressure is constantly changing. At a constant value of the measured value, no electrical pulse will be generated.

Types and varieties of excess pressure sensors

DI according to the type of operation can be divided into two large groups: analog and digital. The difference between them lies in the principles of operation, control and signal transmission. In general, all such devices are made in approximately the same way and are a system with a sensor unit and a control unit. It is in these blocks that an analog or digital principle of operation and data transmission can be used.

There are different types of sensors based on the media they can work with. There are multifunctional varieties, as well as instruments for measuring pressure in liquid or gaseous media. Some models can work in aggressive conditions, for example, used in the chemical industry. Such models are equipped with additional protection.

As additional elements to such devices in industry, pressure difference sensors (differential) are used, which allow measuring pressure levels at the points of difference between high and low. The devices are easily installed in a common network and allow you to read and analyze maximum information from control areas. Indicators can be monitored by any means, including software.

The available range of similar products should be indicated:

• Sensors for general use (universal);
• Differential models;
• Models separately for high and low pressure;
• Devices equipped with special relays;
• High-precision instruments designed for special environments.

Areas of application

The gauge pressure meter is used as a control element in a wide variety of fields. These can be systems for monitoring and regulating low- and high-temperature media, including viscous liquids and polymers. Similar products are also widely used as measuring elements for gases. As for the spheres, excess pressure sensors are used in industry, aircraft manufacturing, shipbuilding, supplying high-temperature gases and liquids, in housing and communal services and other areas.

The selection of sensors is large enough to cover the possibility of solving pressure control problems in almost any situation and in any system. The devices differ in sensitivity, type of mounting socket, and type of electrical connection. The choice is made based on the required measurement parameters, and most importantly, based on the working environment, especially if it has a certain aggressiveness towards metals. Each device has a detailed description of acceptable operating conditions.

Advantages and quality characteristics

Unlike standard sensors, devices for working with excess pressure necessarily have an increased degree of insulation of internal units, as well as housing strength. The sensors are capable of operating in a wide temperature range - from -40 to +80 degrees Celsius. The products are protected from moisture and dust and equipped with an intrinsic safety system.

The price of the product is low and depends on its type, as well as technical features. Before sale, all meters undergo special testing for data accuracy, durability and safety. You can buy an excess pressure sensor at by placing an order on the page with the selected devices.

is one of the leading manufacturers of products for industrial automation in Russian cities: Moscow, St. Petersburg, Novosibirsk, Yekaterinburg, Nizhny Novgorod, Kazan, Chelyabinsk, Omsk, Samara, Rostov-on-Don, Ufa, Krasnoyarsk, Perm, Voronezh, Volgograd , Krasnodar, Ryazan.

Types of pressure sensors

Thus, in the food and chemical industries, an intelligent absolute pressure sensor that measures relative to absolute vacuum has become widely used. Note that it is precisely this measurement that is used in gas, steam and thermal energy metering units to bring the flow rate to standard conditions.

A differential pressure sensor allows you to solve problems of measuring the flow of the measured medium. The principle of its operation is to measure the pressure difference between two cavities - positive and negative. Can be used to measure flow using restriction devices. The constriction device in the pipeline represents a local resistance, when passing through which the nature of the flow changes. Immediately before the constriction device, the pressure of the medium increases, and after it it decreases. The greater the difference at the inlet and outlet of the restriction device, the greater the flow rate of the medium flowing through the pipe.

In addition, such a sensor allows you to take into account the volume of liquid not only in the pipe, but also in the container by measuring the pressure of the liquid column on the positive membrane and, if necessary, measuring the negative pressure cavity under the dome of the container, to eliminate the influence of saturated vapors. This method is called hydrostatic.

In systems of automatic monitoring, regulation and control of technological processes, one cannot do without such a device as an excess pressure sensor. It can be used as part of water heat supply systems, and also be included in units for commercial and technological metering of liquids, gas and steam.

Mechanical and electronic pressure switches

An uncontrolled drop in pressure levels in the heating system can lead to serious problems. There can be many reasons for such a situation. To ensure the integrity and trouble-free operation of the entire system, special protective fittings are used, which includes a pressure switch (PR). These devices are designed to help avoid an emergency decrease in pressure levels, and therefore prevent airing, improper circulation, and boiling of heating equipment.

At NPP Proma you can buy a pressure switch at a fairly attractive price. At the same time, uncompromising product quality is guaranteed. Our own developments with the help of a special design bureau and high-tech production allow us to be confident that the pressure switches we offer for boilers strictly correspond to all the declared characteristics.

Pressure transducer. general information

Model range of overpressure sensors

Tasks and examples for selecting a specific type of sensor

The semi-batch reactor problem

Let us assume that there is a semi-continuous reactor with a capacity of 1000 L with 50 kg of zinc inside under a pressure of 1 atm. and a temperature of 25°C. 6M hydrochloric acid flows into the reactor at a rate of 1 L/min and reacts with zinc to produce zinc chloride for use in another process.

A) What factors should be considered?

B) Tell me if the valve fails at an operating pressure of 4 atm. (i.e. it will not close and the reactor will be flooded with HCl) What pressure can you safely set the breakpoint to?

C) What type of sensor should be used?

Solution:

Factors to consider:

1. Process Hydrochloric acid is very, very corrosive (especially at such a high molarity), and thus whatever sensor you choose must be able to withstand the corrosive nature of the process.

Shutdown point

Taking into account the rapid increase in pressure as estimated in point (2) and valve failure at 4 atm, the cut-off point should be approximately 3 atm

Sensor type:

Given the types of sensors we have discussed, we can immediately dismiss vacuum sensors as they operate at very low pressures (almost a vacuum, hence the name). We can also discard differential pressure sensors since we are not looking for differential pressure across the tank.

Since we want to achieve high sensitivity, we must use electrical components

Considering the pressure range (3 atm; max ~ 0.3 MPa), a capacitive element would be optimal because it is durable and works well in a low pressure system.

Taking into account the corrosion activity in a system containing HCl, a membrane can be used as an elastic element. The membranes are also quite durable and provide fast response times.

This combination will likely be housed in a durable, glycerin/silicone filled housing to protect the sensor from degradation.

So, in the end, we select a sensor that will use a diaphragm as an elastic element, a capacitive element as an electrical component, and a corrosion-resistant housing.

Example 2

Your manager told you to add a pressure sensor to a very expensive and important piece of equipment. You know that a piece of equipment operates at 1 MPa and at very high temperatures

Which sensor would you choose?

Solution

Since the piece of equipment you are dealing with is very expensive, you need a sensor that has high sensitivity. An electrical sensor would be suitable because you could connect it to a computer for a quick and easy reading. Additionally, you should choose a sensor that will operate at 1 MPa and can withstand high temperatures. From the information presented in this article, you know that there are many sensors that will operate at 1 MPa, so you must decide regarding other influencing factors. One of the most sensitive electrical sensors is the capacitive type sensor. It has a sensitivity of 0.07 MPa. A capacitive sensor usually has a diaphragm as an elastic element. The membranes have a fast response time, are very accurate and operate at 1 MPa.

Types of pressure sensors and their purpose

Sensors for measuring pressure are presented in several modifications, differing in technical capabilities. Depending on the model, the sensors are designed to operate with different pressure and temperature ranges of the working environment. As a standard, the devices have transistor or analog control outputs for transmitting output signals.

A separate group of devices is distinguished - pressure sensors-relays, which have a main or additional relay control output. Pressure switches are distinguished by their versatility of use and lower cost compared to other types of devices.

The main criterion for choosing a sensor is the type of pressure being measured, based on which all devices are divided into:

• absolute pressure sensors for monitoring readings relative to absolute zero,
• differential (relative) pressure sensors for measuring readings relative to a set value,
• gauge pressure sensors for measuring excess readings relative to atmospheric pressure,
• hydrostatic sensors for measuring the hydrostatic pressure of the control medium,
• vacuum (vacuum) sensors for measuring the corresponding type of pressure.

Pressure sensors are available as separate devices or can be integrated into multifunctional devices. The choice of pressure sensor depends on the characteristics of the substance being measured, the operating environment conditions, the range being measured, as well as the level of sensor sensitivity and measurement accuracy.

You can select and buy a pressure sensor in the RusAutomation online store...

Types of sensors

Oil sensors are classified according to the principle of their operation. There are two main types of these devices:

1. Low pressure alarm sensors that send a signal to a lamp that lights up on the instrument panel when the lubricant level in the engine is critically low.
2. Sensors measuring engine lubrication pressure, showing the current indicator displayed on the dashboard on a digital or dial indicator.

Mechanical design

The mechanical pressure sensor is currently practically not used. It consists of two parts - membrane and measuring. They are connected to each other by a tube filled with oil. After starting the engine, the oil pressure increases and the membrane bends. It moves, causing the rod of the measuring part of the device to move. This movement is transmitted through a special mechanism to the arrow of the sensor’s analog scale, as a result of which the driver sees the current oil pressure in the system.

These sensors are bulky and there are problems with their accuracy, such as thermal expansion of the oil. Nevertheless, based on such devices, diagnostic verified pressure gauges have been developed, with the help of which you can monitor the actual pressure in the engine lubrication system.

Electrical and electronic

An electric or electronic oil pressure sensor is installed on the vast majority of modern cars. There are differences between these two types:

1. The electronic or emergency pressure sensor operates as a logical element in yes or no mode. If it lights up while the engine is running, this is a signal to the driver that the pressure has dropped below the permissible norm.
2. An electrical or oil control sensor, similar to a mechanical one, shows the oil pressure in the engine in real time. All data is displayed on a display or arrow indicator.

In some cars, for example, powerful tractors or sports models, both sensors are installed in parallel so that the driver can monitor the condition of the engine and react in time to oil starvation, and at the moment of a critical drop in pressure, stop immediately to avoid engine damage.

The emergency sensor is a membrane mechanism with a metal rod to which a contact is attached. The second contact is fixedly attached to the sensor body. When the engine is not running, they are in the closed position and the lamp on the instrument panel is on. After starting, the pressure increases and the membrane bends under the pressure of the engine oil, the rod begins to move and the circuit opens - the indicator on the instrument panel goes out. If the pressure is not enough to bend the membrane, the circuit does not open and the lamp continues to burn.

The operating principle of the control one is similar - it also works from a membrane that bends under oil pressure. But a slider is attached to it through a movable mechanism, moving along the rheostat, changing the resistance and current strength in the circuit. Depending on this, the measuring part of the sensor provides the current oil pressure in the engine lubrication system. Sometimes, instead of a rheostat, such devices use semiconductor or bimetallic converters, but the principle of their operation remains unchanged and depends on the movement of the membrane.

Working principle of the water pressure sensor

A pressure sensor is a device whose physical parameters change depending on the pressure of the medium being measured; these can be gases, liquids, steam. When the measured medium in which the pressure sensor is located changes, its output unified pneumatic, electrical signals or digital code also changes.

Principles of using a pressure sensor

The device consists of a primary pressure transducer, which includes a sensing element and a pressure receiver, a secondary signal processing circuit, housing parts of various designs and an output device.

The main difference between each pressure sensor is the accuracy of pressure registration (measurement ranges from 0 ... 6 bar to 0 ... 60 bar), which depends on the principle of converting pressure into an electrical signal: piezoresistive, strain gauge, capacitive, inductive, resonant, ionization.

Methods for converting pressure into an electrical signal

• strain gauge

The sensing elements of the sensors are based on the principle of measuring the deformation of strain gauges soldered to a titanium membrane, which is deformed under pressure.

• piezoresistive

Based on integral sensitive elements made of monocrystalline silicon. Silicon converters have high time and temperature stability. To measure the pressure of clean, non-aggressive media, so-called Low cost solutions are used - solutions based on the use of sensitive elements either without protection or with silicone gel protection. To measure aggressive media and most industrial applications, a pressure transducer is used in a sealed metal-glass housing, with a stainless steel separating diaphragm that transmits the pressure of the measured medium through a silicone liquid.

• capacitive

Capacitive converters use the method of changing the capacitance of a capacitor when the distance between the plates changes. Ceramic or silicon capacitive primary pressure transducers and transducers made using an elastic metal membrane are known. When the pressure changes, the membrane with the electrode is deformed and the capacitance changes. In a ceramic or silicon cell, the space between the plates is usually filled with oil or other organic liquid. The disadvantage is the nonlinear dependence of the capacitance on the applied pressure.

• resonant

The resonance method is based on wave processes: acoustic or electromagnetic. This explains the high stability of the sensors and the high output characteristics of the device. Disadvantages include the individual characteristics of pressure conversion, significant response time, and the inability to carry out measurements in aggressive environments without losing the accuracy of the device readings.

• inductive

Based on registration of eddy currents (Foucault currents). The sensitive element consists of two coils insulated between each other with a metal screen. The transducer measures the displacement of the membrane in the absence of mechanical contact. An alternating current electrical signal is generated in the coils in such a way that the coils are charged and discharged at regular intervals. When the membrane is deflected, a current is created in the fixed main coil, which leads to a change in the inductance of the system. Shifting the characteristics of the main coil makes it possible to convert the pressure into a standardized signal, its parameters directly proportional to the applied pressure.

• ionization

Ionization method - recording the flow of ionized particles. Tube diodes are an analogue. The lamp is equipped with two electrodes: a cathode and an anode, as well as a heater. In some lamps the latter is absent, which is due to the use of more advanced materials for electrodes. The advantage of such lamps is the ability to record low pressure - right up to deep vacuum - with high accuracy. However, it should be strictly taken into account that such devices cannot be operated if the pressure in the chamber is close to atmospheric. Therefore, such converters must be combined with other pressure sensors, for example, capacitive ones. The dependence of the signal on pressure is logarithmic.

Recording pressure sensor signals

Signals from pressure sensors are slowly changing. This means that their spectrum lies in the ultra-low frequency region. In order to digitize such a signal with high accuracy, it is necessary to suppress the high-frequency part of the spectrum, which consists entirely of interference. This is especially true in industrial settings. Integrating ADCs are used specifically for inputting slowly varying signals. They do not measure the instantaneous value of the signal (which changes under the influence of interference), but integrate the signal function over a given period of time, which is certainly less than the time constant of the processes occurring in the controlled environment, but is certainly greater than the period of the lowest frequency interference

What are the differences between a pressure sensor and a pressure gauge?

A pressure gauge is a device designed to measure (not convert) pressure. In a pressure gauge, the readings of the device depend on the pressure, which can be read from its scale, display or similar device.

Need a pressure sensor?

To select the required pressure sensor to work with a frequency converter or other device, please contact the electrical engineering company ENERGOPUSK: (495) 775-24-55.

Pressure Sensors

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Sensitivity

Different processes require different levels of precision. In general, the more accurate a sensor is, the more expensive it is, so it will be cost-effective to select sensors that can best meet the required accuracy. There is also a trade-off between accuracy and the ability to quickly detect changes in pressure. Therefore, in processes where pressure varies greatly over short periods of time, it is not practical to use sensors that take longer to give accurate pressure readings, even though they could give more accurate readings.

Types and operation of excess pressure sensors

The most common are piezoelectric, strain gauge and capacitive analogue or digital gauge pressure sensors. Both groups of sensors are integrated into a common automated process control system. The sensors consist of a cavity with a sensitive sensor and an electronic unit with additional devices. Pressure affects the sensor, which changes its conductive characteristics. The electronic unit recognizes changes in the state of the sensor, generates an output electrical signal and controls additional devices (displays, alarms, relays). A number of sensor models are capable of measuring excess pressure in aggressive environments.

Capacitive devices

These devices are the most popular because they have a simple design, operate stably and are easy to maintain. The design consists of two electrodes located at a certain distance from each other. It turns out to be a kind of capacitor. One of its plates is a membrane; pressure (measurable) acts on it. As a result, the gap between the plates changes (proportional to the pressure). From your school physics course, you know that the capacitance of a capacitor depends on the surface area of ​​the plates and the distance between them.

When working in a pressure sensor, only the distance between the plates changes - this is quite enough to measure the parameters. Electronic oil pressure sensors are built according to exactly this scheme. The advantages of this type of structure are obvious - they can work in any environment, even aggressive ones. They are not affected by large temperature changes or electromagnetic waves.

Industrial applications of pressure sensors

To measure the excess pressure of the working medium in pipelines, mechanical instruments are used that are reliable and do not depend on the presence of electric current. They are used to determine the characteristics of the working environment “on site”. More advanced electrical devices are used to construct mnemonic diagrams and remote control of pipeline fittings or units. They usually work in tandem with mechanical ones.

Without reliable pressure transducers, the operation of heat and water supply networks is impossible.

Performances

Sensor selection criteria

For a pressure-controlled system to operate correctly and efficiently, it is important that the pressure sensor used can provide accurate readings as needed and over an extended period of time without the need for repair or replacement while the system is operating. There are several factors that influence the suitability of a particular pressure sensor for a particular process.

The main ones are:

• characteristics of the substances used in the environment in which the device will be used;
• environmental conditions;
• pressure range;
• the level of accuracy and sensitivity required in the measurement process.

Sensor device

For this device, the parameters may change depending on changes in the parameters in the measured medium, for example, liquid, gas, or steam. In the sensor, the characteristics of the measured medium are converted into a unified code for displaying indicators on a pointing device.

The sensor consists of a primary transducer, which includes a sensing element - a pressure receiver, secondary signal processing circuits, and various parts of the housing. In some cases, it is equipped with sealing parts for operating conditions in humid and aggressive environments.

Optoelectronic sensors

They simply detect pressure and have high resolution. They have high sensitivity and thermal stability. They work on the basis of the interference of light, using a Fabry-Perot interferometer to measure small movements. Such electronic pressure sensors are extremely rare, but are quite promising.

Main components of the device:

1. Optical converter crystal.
2. Diaphragm.
3. Light-emitting diode.
4. Detector (consists of three photodiodes).

Fabi-Perot optical filters, which have a slight difference in thickness, are attached to the two photodiodes. Filters are silicon mirrors with a reflective front surface. They are coated with a layer of silicon oxide, and a thin layer of aluminum is applied to the surface. The optical transducer is very similar to a capacitive pressure sensor.

Classification of devices according to operating principle

Based on the principle of operation or the method used in converting the input signal into an electrical output, measurement sensors are classified:

• Strain gauge method. Sensing parts measure resistance when exposed to a strain gauge attached to an elastic element, which deforms when exposed to pressure.
• Piezoresistive method. Works on the basis of integrated sensitive parts made of silicon. Silicon converters are highly sensitive due to the ability to change the resistance of the semiconductor. To measure characteristics in non-aggressive environments, Low cost is used - a method of equipment design when the sensitive element is not equipped with any degrees of protection. In the case of operation in an environment where it is possible that the sensor may be exposed to an aggressive substance, the sensitive element is equipped with a sealed housing with a separating diaphragm made of steel, which transmits pressure through silicon liquid.
• Capacitive method. The main part of a sensor operating using this method is a capacitive cell. Its work is to change the electrical capacitance between the capacitor and the measuring membrane, depending on. The main advantage is protection from deformation; in the absence of pressure, the membrane restores its shape, and calibration of such a sensor is not required. And also the high stability of characteristics is due to the small influence of temperature error due to the small volume of liquid that fills the internal volume of the cell.
• Resonance method. The basis for work on this principle is the change in the resonance frequency of an oscillating element during its deformation. Disadvantages include a long response time and the inability to work in aggressive environments without loss of measurement accuracy.
• Inductive method. Based on registration of vortex bonds. The measuring element consists of two insulated coils with a metal screen. The transmitter measures the displacement of the membrane without actual contact between the two surfaces. Electric current is generated in the coils in such a way that the charge and discharge of the coil occurs at equal intervals of time. When the position of the membrane changes, a current is created in the fixed coil, followed by a change in the inductance of the system. The displacement of the main coil data makes it possible to convert the data into a standard signal, which in its parameters is proportional to the applied pressure.
• Ionization method. It works on the principle of registering a flow of ionized particles, like a lamp diode. The lamp is equipped with two electrodes, a cathode, an anode, and a heater in some cases. The advantage is the ability to record data in low-pressure environments, including vacuum, but such equipment cannot be operated at atmospheric pressure.
• Piezoelectric method. The idea is based on the piezoelectric effect, in which a piezoelectric element creates an electrical signal proportional to the effect of the measured medium on it. Used to measure constantly changing acoustic and pulsed environments. Has a wide range of dynamic and private data measurement. It has low weight, dimensions and high reliability when used in harsh conditions.

Conclusions:

Application and selection of excess pressure sensors

Selecting excess pressure sensors is a technically complex task that depends on the type of pressure, characteristics of the medium being measured, external conditions, metrological parameters of the sensor, type of sensor connection and its additional indication capabilities, variety of analog output signals, support for generally accepted digital industrial protocols, etc. d. Before purchasing an overpressure sensor for standard use, it would be more advisable to choose it from the most commonly used models:

• industrial gauge pressure sensor DMP331 for general use
• sensor models DMP 333, DMK 331 for measuring medium and high pressure
• DMP 331P sensor for the food industry with different connection types
• precision sensor DPS 300 for particularly low gas pressures
• indicator sensors, alarm sensors and relay sensors
• specialized sensors (high-precision, hydraulics, freon, viscous or aggressive media)

Additional functions greatly influence the cost of the device and the price of excess pressure sensors can vary significantly. To buy the right sensor at the best price, contact our specialists.