intrinsically safe pressure transducer

The low differential pressure transmitter is a type of instrumentation equipment commonly used in modern industrial production, which can be called the “eye” of modern industrial production. In the production process, it can observe and control the pressure, flow, temperature, liquid level, and other measurement data of the entire production process. And then the data can be transferred to the logic algorithm in the central control system (DCS or PLC) through low DP data exchange. At the same time, adjustment is made by the regulator or control unit. Finally, the control of the production target values is completed. Thus, the low differential pressure transmitter is an important prerequisite for the establishment of a good control loop. Pressure transmitters and differential pressure transmitters are typical representatives of the “eye”, which are widely used due to their high precision and stability.

 

1. The classification of the low differential pressure transmitter 

The function of the low differential pressure transmitter, in simple terms, is to convert the displacement or force of the elastic load cell into a standard electrical signal. Based on the composition and working principle, it can be divided into force-balance transmitter and displacement transmitter while the latter is generally used in the glass production line. Based on the measurement accuracy and objective, it can be divided into the micro differential pressure transmitter, the differential pressure transmitter, and the pressure transmitter. And besides, according to the signal transmission and power supply mode, it can be divided into a two-wire transmitter and a four-wire transmitter.

 

2.  The application of the low differential pressure transmitter

Based on what we have learned, it is realized that the displacement transmitter is more approved by the market than the force-balance transmitter in today’s measurement field. The same is true in the design process of the glass production line. However, in terms of differences in measurement objectives and accuracy, there are still differences in the selection of the low differential pressure transmitter.

(1) The high-precision micro-differential pressure transmitter is used in the furnace to measure the pressure of the kiln, which is one of the fundamental safety and measurement objects. At this moment, the pressure pipe of P1 needs to go deep inside the furnace wall while the pressure of P2 is the atmospheric pressure at the temperature close to that of the furnace. The pressure pipe that is finally connected to the low differential pressure transmitter should be the average value of the pressure on both sides of the furnace. Next, based on the principle of the transmitter, the gauge pressure inside the furnace can be obtained through P1-P2.

(2) The low differential pressure transmitter and the orifice plate flowmeters throttling device can be used for the measurement of natural gas, hydrogen, oxygen, and combustion-supporting airflow. A disk with a central hole is inserted into the pipeline. When the fluid passes through the orifice plate, the cross-section of the flow beam is reduced, causing a local difference in flow velocity and a relatively significant pressure difference. The flow rate of the fluid is proportional to the square root of the pressure difference before and after the throttle element under certain conditions. In the formula, Q is the measured flow, F0 is the opening area of the orifice plate, α is the flow coefficient, ρ is the liquid density, P1 is the inlet pressure of the orifice plate and P2 is the outlet pressure of the orifice plate.

In addition to its important role in the key measurement areas in the glass production line, the low differential pressure transmitter has many derivative applications, such as the measurement of the height change of the glass liquid level and the liquid level height, etc, which will not be described in detail here.

 

3. The development of the low differential pressure transmitter

Compared with liquid, it is more complicated to measure gas flow due to its compressibility. The volumetric flow rate Q of the gas is a function of the differential pressure (P1-P2) and the density ρ while the density is a function of the current temperature and pressure of the gas. In the practical application, there will be a large measurement error due to the difference between the current density of the medium and the density during design. Therefore, temperature and pressure compensation should be performed on it.

In the past, designers install both thermal resistance and a pressure transmitter near the location where the gas pipeline is set up the flowmeter. All three groups of signals are entered into the DCS system, and the compensation calculation is completed with the formula in the computer system. However, this model is gradually being replaced nowadays. With the emergence of a new generation of multi-parameter intelligent transmitters, this type of transmitter comprehensively improves the accuracy, reliability, and long-term stability of the low differential pressure transmitter by using a microprocessor as a basis.

electronic pressure transducer

The intelligent or mechanized operation of all walks of life can’t be separated from the development of science and technology and machines, which also gradually reduces the load of manual labor, greatly improves the efficiency. Pressure transducer is the most common sensing instrument in industrial practice. It is widely used in various industrial automation environments, such as water conservancy and hydropower, intelligent buildings, aerospace, military, petrochemical and many other industries. However, because it is indirectly related to your daily life, you will not know much about it, so Alpha Instruments is going to talk about it in detail.

Pressure transducers can be divided into a variety of different types, such as heavy-duty type. It is usually used in transportation to maintain the performance of heavy-duty equipment mainly by monitoring the pneumatic, hydraulic, brake pressure and air brake and other key systems of pressure, flow, and liquid level. This pressure transducer has a housing, a metal pressure connection, and a setting device for a high-level signal output. It is cylindrical in appearance with a pressure connection at one end and a connector at the other. It can be used in extreme temperature and electromagnetic interference environment. Customers in the industrial and transportation fields can use the industrial pressure transducer in the control system to effectively monitor and feedback the pressure of cooling liquids, lubricating oil and other fluids. Once problems are found, timely measures can be taken to solve them.

The above is the main classification of pressure transducers and their application in the industrial field.

surface mount pressure sensor

The low differential pressure sensor is powered by 5V with an output of 0.25-4V. Although it is the analog output, the internal linearization and temperature compensation are all realized digitally, ensuring high accuracy and resolution ratios (up to 0.05 Pa). It is thus unsusceptible to temperature.

The low differential pressure sensor has two specific output modes, including linear and square output which are completely interchangeable. Relying on simple peripheral circuits, such as 0-10V output or other interfaces, high-quality transmitters can be produced.

Its leading performance is based on the integration of sensing elements, signal amplification, and A/D conversion into the same silicon chip. The thermal sensor element measures differential pressure. Compared with other thermal differential pressure sensors, it requires less air and can work under the extremely harsh environment in a safe and reliable way. Compared with the diaphragm sensor, the low differential pressure sensor has a wider measuring range, more stable performance and more excellent renaturation in the section of low differential pressure. In addition, the low differential pressure sensor can withstand large instantaneous pressure and is not sensitive to the installation direction.

The low differential pressure sensor has the following characteristics:

1. Accuracy:

(1) Digital accuracy: ±0.05%

(2) Full performance: ±0.25F.S

2. Strong performance for pressure measurement, differential pressure measurement and flow measurement

3. Range ratio: 100:1

4. Stability: 0.25%, 60 months

5. Measurement rate: 0.2S

6. Stainless steel cover that is easy to install and ensures excellent cold and thermal stability

7. Process connections are compatible with other products for optimal measurement

8. Adoption of the intelligent transmitter with a 16-bit computer

9. Standard current output of 4-20mA, protection mechanism for mis-wiring, environmental design, and compliance with RoHS standard

electronic pressure transducer

When it comes to pressure transducer, perhaps we are most familiar with its application in medical devices, such as ventilators, electronic blood pressure monitors and other products. But in fact, pressure transducers are also one of the most used measuring devices in automatic control in the petrochemical industry. In large-scale chemical projects, almost all pressure transducer applications are included, such as differential pressure, absolute pressure, gauge pressure, high pressure, slight differential pressure, high temperature, low temperature, and remote flange pressure transducer of various materials and special processing. Almost the petrochemical industry’s demand for pressure sensors is mainly concentrated in three aspects: reliability, stability and high precision. Among them, reliability and many additional requirements, such as turndown ratio, bus type, depend on the transmitter’s structural design, mechanical processing level and structural materials. The stability and high accuracy of the pressure transmitter are mainly guaranteed by the stability and measurement accuracy of the pressure transducer.

The measurement accuracy of the pressure transmitter corresponds to the measurement accuracy and response speed of the pressure transducer, and the stability of the pressure transmitter corresponds to the temperature characteristic, static pressure characteristic and long-term stability of the pressure transducer. The demand for pressure transducer uses in the petrochemical industry is reflected in measurement accuracy, rapid response, temperature characteristics and static pressure characteristics, and long-term stability.

The material of pure monocrystalline silicon has low fatigue, and the pressure transducer made of this material has long-term stability. At the same time, the pressure transducer is easy to be integrated with the temperature sensor, which increases the temperature compensation accuracy and greatly improves the temperature characteristics and measurement accuracy of the sensor, which can well meet the demand for pressure transducer in the petrochemical industry.

Pressure is one of the most important parameters in industrial production. In order to ensure the normal operation of production, pressure must be monitored and controlled to achieve automatic control, safety monitoring and alarm functions. Pressure transducers are widely used in pressure switches and vacuum equipment, flow control, air conditioning system fan control, etc. Accurate measurement is a key requirement, and the ability to withstand harsh environments is also important. The transducers produced by Alpha Instruments have always enjoyed high reputation and are your best choice!

electronic pressure transducer

1. Calibration is needed by pressure transmitter

After being used for a while, the measurement performance of the pressure transmitter may be changed, and the phenomena of zero drift and increasing measurement error will appear. Therefore, it is necessary to carry out regular calibration of the pressure transmitter. The calibrator should be 3 times more accurate than the required calibration accuracy. Standard pressure values of 0%, 25%, 50%, 75%, and 100% are input successively into the transmitter via the pressure calibrator in a forward and reverse manner, to detect whether the output signal of the electric current is within the allowed accuracy range. If out of range, it needs to be calibrated.

 

2. Calibration methods of pressure transmitter

The calibration methods are as follows (4~20mA output):

(1) Input the standard pressure of 4mA with pressure calibrator and adjust the ZERO potentiometer to make sure that the electric current output falls within the accuracy range;

(2) Input the standard pressure of 20mA with pressure calibrator and adjust the SPAN potentiometer to make sure that the electric current output falls within the accuracy range;

(3) ZERO and SPAN potentiometers are mutually restrictive. Repeat step (1) and step (2) until both the current outputs of 4mA and 20mA meet the accuracy requirements, and then check whether the current outputs of 25%, 50%, and 75% meet the accuracy requirements. If so, it indicates the calibration of pressure transmitter produced by pressure transmitter manufacturer is qualified.

Alpha Instrument Inc. is specialized in the development and manufacturing of low differential pressure sensors, which have been used in heating ventilation air conditioning, critical environment, medical industry, semiconductor equipment, and other fields. Our innovatively designed products provide long-term stability, higher sensitivity, and higher overvoltage capacity. Welcome to contact us to buy!

cost effective pressure sensor

Ⅰ. Extensive research fields on the pressure transmitter

Nowadays, extensive researches on pressure transmitter are carried out around the world, diving into almost every industry.

 

Ⅱ. Development trend of pressure transmitter

1. Intelligence

Due to the emergence of intelligence technology, some microprocessors can be added to the integrated circuit, equipping the pressure transmitter with functions of automatic compensation, communication, self-diagnosis, logical judgment, etc.

2. Integration

More and more pressure transmitters have been integrated with other measurement transmitters to establish measurement and control systems. An integrated system can improve operation speed and efficiency in process control and factory automation.

3. Miniaturization

There is a growing demand for micro pressure transmitters as this kind of transmitter can work under extremely harsh environments, which requires few maintenance and produces small environmental affects.

4. Standardization

A series of standards about the design and manufacture of transmitters have been established.

5. Generalization

Another development trend of pressure transmitter lies in its expansion from the mechanical industry into other fields, such as automotive components, medical instruments, and energy and environment control systems.

negative pressure transducer

Ⅰ. Preparation work before installation of pressure transmitter

1. Check the equipment: Since the equipment is designed by different pressure transmitter suppliers and features various models, it is necessary to determine the transmitter corresponding to each tag number according to the range, design and installation mode, and the material required by the process medium.

2. Determine the installation position: A variety of pressure transmitters can be installed anywhere if they are waterproof and dustproof. However, considering the convenience of daily operation and maintenance, and to extend service life and ensure reliability, the installation position should meet the following requirements:

(1) There is enough working space around, and the distance from adjacent objects (in any direction) is more than 0.5m;

(2) There is no serious corrosive gas around;

(3) It is not exposed to the surrounding thermal radiation and direct sunlight;

(4) To prevent the interference caused by the vibration of transmitter and pressure conducting tube (capillary), the pressure transmitter should be installed in the place without vibration.

 

Ⅱ. Installation requirements of pressure transmitter

1. Installation requirements of pneumatic pressure transmitter

(1) The pressure transmitter should be installed on the vertical or horizontal pipeline without strong vibration.

(2) The surrounding environment should be free of impurities corrosive to carbon steel, copper and alloy.

(3) For the convenience of maintenance and zero adjustment, adequate space should be reserved on the top and sides of the equipment.

(4) The pressure transmitter should be installed near (generally no more than 5m) the site requiring pressure measurement as much as possible.

(5) When the measured pressure is zero after installation, the output pressure of pressure transmitter should be 20KPa, otherwise it should be adjusted.

(6) The air source used for pressure transmitter should be filtered and purified compressed air.

 

2. Installation requirements of electric pressure transmitter

(1) Installation requirements for measuring gas pressure

A. When measuring the gas pressure, the pressure-relief point of the pressure measuring pipeline must be selected at the upper half of the pipeline to prevent liquid accumulation in the pipeline.

B. Flush valve should be installed at the front of pressure transmitter to prevent liquid or dirt from entering the transmitter.

C. When installing the pressure transmitter on the pipe throttling device, the pressure measuring point must be located within the area where the vertical line and the horizontal line meet at a 45-degree angle.

(2) Installation requirements for measuring steam pressure

When measuring the steam pressure, the pressure measuring point must be located within the area where the vertical line and the horizontal line meet at a 45-degree angle. The gas collector should be installed at the highest point of the pressure measuring point and the gas should be discharged regularly to ensure the measurement accuracy of the transmitter.

(3) Installation requirements for measuring the pressure of corrosive medium

When measuring the pressure of corrosive medium, an isolation device should be installed in front of the pressure transmitter and space liquid should be injected into it.

cost effective pressure sensor

The static characteristic of the low differential pressure sensor refers to the relationship between input and output when the input quantity is in steady state or a slowly changing signal. On account of at this time the input quantity and output quantity are not related to time, so the relationship between them, that is, the static characteristic of the low differential pressure sensor can be an algebraic equation without time variables, or using the input quantity as the abscissa and the corresponding output quantity as the ordinate to describe the characteristic curve. The main parameters that characterize the static characteristics of the low differential pressure sensor are linearity, sensitivity, hysteresis, repeatability, drift, etc.

(1) Linearity:

Linearity refers to the degree to which the actual relationship curve between the output quantity and input quantity of the low differential pressure sensor deviates from the fitting straight line. It is defined as the ratio of the large deviation value between the actual characteristic curve and the fitting straight line to the full-scale output value within the full range.

(2) Sensitivity: 

Sensitivity is an important indicator of the static characteristics of a low differential pressure sensor. It is defined as the ratio of the increment of the output quantity to the increment of the corresponding input quantity that caused the former. And the sensitivity is represented by S.

(3) Hysteresis: 

The phenomenon that the input and output characteristic curves of the low differential pressure sensor do not coincide during the change of the input quantity from small to large (positive stroke) and from large to small (reverse stroke) is called hysteresis. For the input signals of the same size, the positive and reverse stroke output signals of the low differential pressure sensor are not equal, and this difference is exactly called the hysteresis difference.

(4) Repeatability:

Repeatability refers to the degree of inconsistency of the characteristic curve obtained when the input quantity of the low differential pressure sensor changes continuously for several times in the same direction within the full range.

(5) Drift:

The drift of the low differential pressure sensor refers to the phenomenon that output quantity of the differential pressure sensor changes with time when the input quantity is unchanged, which is called drift. There are two reasons for drift: one is the structural parameters of the low differential pressure sensor itself; the other one is the surrounding environment (such as temperature, humidity).

cost effective pressure transducer

In the process of using the low differential pressure sensor, various bad experiences may occur due to inattention to some details. Today some experience of using the low differential pressure sensor is summarized to share with you, hoping to help you solve problems quickly.

1. The low differential pressure sensor has a large deviation compared with the pointer pressure gauge.

The appearance of deviation is a normal phenomenon, just confirm the normal deviation range. Due to the small measuring range of the low differential pressure sensor, the sensing element will affect its output. The pressure sensitive part of the low differential pressure sensor should be axially perpendicular to the direction of gravity during installation and adjust the zero position of the low differential pressure sensor to the standard value after the installation and fixation.

 

2. When the pressure goes up, while the output of the low differential pressure sensor can not go up.

 

In this case, check whether the pressure interface is leaking or blocked firstly, if it is confirmed not, check the mode of connection and the power supply, if the power supply is normal, simply pressurize to see whether the output changes or check whether the sensor zero position has output if there is no change, the sensor is damaged, which may be a problem caused by the instrument damage or other links of the entire system.

3. The output signal of the low differential pressure sensor is unstable

This failure may be a problem with the pressure source. The pressure source itself is an unstable pressure, which is most likely due to the weak anti-interference ability of the instrument or low differential pressure sensor, and the severe vibration of the sensor itself as well as the sensor failure.

electrical pressure transducer

The low differential pressure sensor divides the pressure into two types: positive pressure and negative pressure. The former is used for protective isolation, and the latter is used for isolation and control of infectious diseases transmitted through the air. For example, hospital wards, operating rooms, pharmacies, clean rooms for pharmaceuticals and semiconductor production, life science laboratories, and animal and botanical gardens use positive pressure protection, while the hospital wards for tuberculosis, measles, chickenpox, or SARS patients and biosafety laboratories are isolated by negative pressure to form a protective space for the public.

The low differential pressure sensor, also called negative pressure sensor / positive pressure sensor, is used to accurately measure the small pressure difference between the key area and the adjacent area (usually the adjacent corridor or lobby). These pressure gradients can prevent airborne infectious diseases or pollutants from spreading from the protected area to the contaminated area, and vice versa.

The critical medical environment has the characteristics of extremely low differential pressure measurement, with a full scale of 25Pa (0.0036 PSI). With the increasing importance of building energy consumption, the environmental differential pressure requirements are continuously decreased under the premise of ensuring safety.