Home > What is a pressure transmitter

What is a pressure transmitter


What is a pressure transmitter?



What is a pressure transmitter?

This article introduces the basic concepts of pressure transmitters,

the history of pressure transducers,

the working principle of pressure transmitters,

classification, main performance and advantages, and so on.


The concept of pressure transmitter

Pressure transmitter, or pressure transducer,

is a device that converts pressure into pneumatic or electric signals,

for control and remote transmission.


Pressure transducers can convert the physical pressure parameters,

such as, gas and liquid sensed by the load cell sensor,

into standard electrical signals (such as 4~20mADC, etc.),

to supply secondary instruments.

Such as indicating alarm, recorder and regulator for measurement, sign and process change.



The concept of pressure transmitter

History of pressure transmitters


The development of pressure  transducers has generally gone through four phases:


(1) Early, pressure transmitters use large displacement working principles,

such as mercury float differential pressure gauges and bellows type differential pressure transmitters. These transmitters are low precision and cumbersome.


(2) In the 1950s, there was a higher precision force-balanced differential pressure transmitter,

but the feedback force was small,

the structure was complicated, and the reliability, stability and vibration resistance were poor.


(3) In the mid-1970s, with the advent of new processes,

new materials, and new technologies, especially the rapid development of electronic technology,

displacement transmitters with small size and simple structure appeared.


(4) In the 1990s, the rapid development of science and technology,

the accuracy of transmitter measurement improved,

and developed into intelligence.

Digital signal transmission is more conducive to data acquisition.

Different types of diffused silicon piezoresistive transmitters,

capacitive transmitters, differential inductive transmitters, and ceramic capacitive transmitters have emerged.


What is a pressure transmitter?

How does the pressure transmitter work?

Working Principle of pressure transmitter

Pressure transmitter is the most used sensor in industrial practice. It is used in various industrial self-control environments,

involving water conservancy and hydropower,

railway transportation, intelligent building,

production automation, aerospace, military, petrochemical,

oil well, electric power, ship, machine tools,

pipelines and many other industries.

The following introduces the principle and application of some common pressure transmitters.


1. Principle and application of strain gauge pressure transmitter

There are many types of mechanical sensors, such as:

resistance strain gauge pressure transmitter,

semiconductor strain gauge pressure transmitter,

piezoresistive pressure transmitter,

inductive pressure transmitter,

capacitive pressure transmitter, and resonant pressure transmission. And capacitive accelerometers, etc.

But the most used is a piezoresistive pressure transmitter,

which has a very low price, high precision and good linearity. Below we mainly introduce such sensors.

When we understand the piezoresistive pressure transmitter,

we first understand the components of the resistance strain gauge. A strain gauge is a sensitive device,

that converts the strain change on the device under test into an electrical signal. It is one of the main components of a piezoresistive strain transmitter.

The most widely used resistance strain gauges,

are metal resistance strain gauges and semiconductor strain gauges. The metal resistance strain gauge has two kinds of:

filament strain gauges and metal foil strain gauges.

Usually, the strain gauge is bonded to the mechanical strain matrix by a special adhesive.

When the stress changes, due to the force of the substrate,

the strain gauges are also deformed together,

so that the resistance of the strain gauge is changed,

thereby The voltage applied to the resistor changes. The strain gauges have a small change in resistance when stressed.

Typically, such strain gauges form a strain bridge and are amplified,

by a next instrumentation amplifier,

and transmitted to the processing circuit (usually A/D conversion). And CPU) display or actuator.


Internal structure of metal resistance strain gauge

FIG 1. Internal structure of metal resistance strain gauge


As shown in FIG. 1. It is a structural schematic diagram of a strain gauge,

which is composed of a base material,

a metal strain wire or a strained foil, an insulation protection sheet, and a lead wire.

Depending on the application,

the designer can design the resistance of the strain gauge.

But the range of resistance should be noted:

the resistance is too small,

the required drive current is too large, and the heat of the strain gauge causes the temperature to be too high.

Used in different environments,

the resistance value of the strain gauge is changed too much,

the output zero drift is obvious, and the zero adjustment circuit is too complicated.

The resistance is too large, the impedance is too high,

and the ability to resist external electromagnetic interference is poor. Generally, it is about tens of euros to several tens of kiloohms. The working principle of the resistance strain gauge


The working principle of the metal resistance strain gauge is a phenomenon,

in which the strain resistance adsorbed on the base material changes,

with the mechanical deformation,

which is commonly called the resistance strain effect.

The resistance value of the metal conductor,

can be expressed by the following formula:

where:

ρ - the resistivity of the metal conductor (Ω·cm 2 /m)

S - the cross-sectional area of the conductor (cm 2 )

L - the length of the conductor (m)


Taking wire strain resistance as an example,

when the wire is subjected to an external force,

its length and cross-sectional area will change.

It can be easily seen from the above formula that the resistance value will change,

if the wire is subjected to an external force.

When it is stretched,

its length increases, and the cross-sectional area decreases, and the resistance value increases.

When the wire is compressed by an external force,

the length is decreased and the section is increased,

and the resistance value is decreased.

As long as the change in resistance is measured

(usually the voltage across the measured resistance),

the strain of the strained wire is obtained.


2. Principle and application of ceramic pressure transmitter

The corrosion-resistant pressure transmitter, has no liquid transfer,

the pressure acts on the front surface of the ceramic diaphragm,

causing a slight deformation of the diaphragm.

The thick film resistor is printed on the back of the ceramic diaphragm and connected,

into a Wheatstone bridge ( Closed bridge),

due to the piezoresistive effect of the varistor,

the bridge produces a linear voltage signal proportional to the pressure,

which is proportional to the excitation voltage. The standard signal is calibrated to 2.0 / 3.0 according to the pressure range. 3.3 mV/V, etc., compatible with strain gauge sensors. With laser calibration, the sensor has high temperature stability and time stability. The sensor comes with temperature compensation of 0 to 70 ° C and can be in direct contact with most media.


Ceramic is a recognized material that is elastic,

resistant to corrosion, abrasion, shock and vibration.

The thermal stability of ceramics,

and its thick film resistance allow it to operate over a temperature range of -40 to 135 ° C,

with high precision and high stability.

The degree of electrical insulation is >2kV,

the output signal is strong, and the long-term stability is good. High-performance, low-priced ceramic sensors will be the development direction of pressure  transducers. There is a trend to replace other types of sensors in Europe and the United States.

In China, more and more users use ceramic sensors,

instead of diffused silicon pressure transmitters.


What is a pressure transmitter?

3. Principle and application of diffused silicon pressure transmitter

The pressure of the measured medium,

acts on the diaphragm of the sensor (stainless steel or ceramic),

causing the diaphragm to produce a micro-displacement proportional,

to the pressure of the medium,

causing the resistance value of the sensor to change,

and detecting the change by electronic circuitry,

and The conversion outputs a standard measurement signal corresponding to this pressure. 


4. Principle and application of sapphire pressure transmitter

Using strain-resistive operation, silicon-sapphire is used as a semiconductor sensor with unparalleled metrology.


The sapphire is composed of a single crystal insulator element,

which does not cause hysteresis, fatigue and creep;

sapphire is stronger than silicon,

has higher hardness and is not afraid of deformation;

sapphire has very good elasticity and insulation properties (within 1000 OC),

so use Semiconductor sensitive components made of silicon-sapphire are insensitive to temperature changes,

and have excellent operating characteristics even under high temperature conditions;

sapphire has excellent radiation resistance;

besides, silicon-sapphire semiconductor sensitive components have no pn drift.

So, the manufacturing process is simplified,

the repeatability is improved, and high yield is ensured.


Pressure sensors and transducers,

made of silicon-sapphire semiconductor sensitive components,

operate under the toughest operating conditions,

with high reliability, high accuracy, minimal temperature error and cost-effectiveness.


The gauge pressure sensor and pressure transmitter consist of a double diaphragm:

a titanium alloy measuring diaphragm and a titanium alloy receiving diaphragm.

A sapphire sheet, printed with a heterogeneous epitaxial strain sensitive bridge circuit,

is soldered to the titanium alloy measuring diaphragm.

The pressure to be measured is transmitted to the receiving diaphragm

(the receiving diaphragm and the measuring diaphragm are connected by a tie rod).

Under the action of pressure, the titanium alloy receiving diaphragm is deformed.

After the deformation is sensed by the silicon-sapphire sensing element,

the bridge output changes,

and the size of the change is proportional to the measured pressure.


The sensor's circuitry ensures power to the strained bridge circuit,  

and converts the strain bridge's unbalanced signal,

into a uniform electrical signal output (0-5, 4-20mA or 0-5V).

In the absolute pressure sensor and pressure transmitter,

the sapphire sheet is connected with the ceramic base glass solder,

to act as an elastic element,

to convert the measured pressure into strain gauge deformation for pressure measurement.


5. Principle and application of piezoelectric pressure sensor

Piezoelectric materials used in piezoelectric sensors include:

quartz, sodium potassium tartrate, and dihydrogen phosphate. Among them, quartz (silicon dioxide) is a kind of natural crystal. The piezoelectric effect is found in this crystal.

In a certain temperature range, the piezoelectric property always exists,

but after the temperature exceeds this range,

the piezoelectric property is completely Disappeared

(this high temperature is the so-called "Curie point").

Since the electric field changes little with the change of stress

(that is, the piezoelectric coefficient is low),

quartz is replaced by other piezoelectric crystals.

Potassium sodium tartrate has a large piezoelectric sensitivity and piezoelectric coefficient,

but it can only be applied in a low room temperature and humidity environment.

Dihydrogen phosphate is an artificial crystal,

that can withstand high temperatures and relatively high humidity,

so it has been widely used.


The piezoelectric effect is also applied to polycrystals,

such as the current piezoelectric ceramics,

including barium titanate piezoelectric ceramics, PZT, tantalate-based piezoelectric ceramics,

lead magnesium niobate piezoelectric ceramics, and the like. Piezoelectric effect is the main working principle of piezoelectric sensors.

Piezoelectric sensors cannot be used for static measurement,

because the electric charge after external force is saved,

only when the loop has an infinite input impedance.

This is not the case,

so this determines that the piezoelectric sensor can only measure dynamic stresses. Piezoelectric sensors are mainly used in the measurement of acceleration, pressure and force. A piezoelectric accelerometer is a commonly used accelerometer.

It has the characteristics of simple structure,

small size, light weight and long service life.

Piezoelectric accelerometers have found wide application in vibration and shock measurements:

in plane, automobiles, ships, bridges and buildings,

especially in the aerospace and aerospace fields.

Piezoelectric sensors can also be used to measure:

the measurement of combustion pressure inside the engine.

and the measurement of vacuum.

It can also be used in the military industry,

for example, to measure the change in the pressure of the gun bullet in the moment of firing,

and the shock wave pressure of the muzzle. It can be used to measure large pressures as well as to measure small pressures.


Piezoelectric sensors are also widely used in biomedical measurements. For example, ventricular catheter microphones are made of piezoelectric sensors. Because measuring dynamic pressure is so common, piezoelectric sensors are widely used.


What are the types of pressure transmitter?

Among the various types of instruments,

transducers are the most used and widely used,

and the transmitters are generally divided into pressure transmitters and differential pressure  transducers.

Transmitters are used to measure pressure, differential pressure, vacuum, level, flow and density. The transmitter has two-wire system and four-wire system.

There are many two-wire transmitters;

there are intelligent and non-intelligent points, and there are more intelligent transmitters;

there are pneumatic and electric parts, and most of the electric transmitters.

Besides, according to the application,

there are intrinsic safety type (intrinsic safety type) pressure transducer,

and explosion-proof type pressure transducer;

according to the application conditions, the main types of transmitters are as follows:


Low (micro) pressure / low (micro) differential pressure transmitter;

medium / medium differential pressure transmitter;

high pressure / high differential pressure transmitter;

absolute / vacuum / negative pressure differential pressure transmitter;

high temperature / Pressure, differential pressure transmitter;

corrosion resistant / pressure, differential pressure transmitter; easy to crystal / pressure, differential pressure transmitter.


Transmitter selection is usually based on installation conditions,

environmental conditions, instrument performance, economy, and media usage.

In practical applications, it is divided into direct measurement and indirect measurement;

its uses include process measurement, process control and device interlocking.

Common transmitters include ordinary pressure transmitters, differential pressure transmitters,

single-lamp transmitters, dual-lamp transmitters, and plug-in flange transmitters.


types of pressure transmitter

Main performance and advantages of pressure transmitters

Pressure transmitter main performance

1. When the pressure transmitter is used, the measured medium is extensive,

and it can measure oil,

water and paste compatible with 316 stainless steel and 304 stainless steel,

and has certain anti-corrosion ability;


2, pressure transmitter has high accuracy, high stability,

the use of imported original sensors, good linearity, high temperature stability;


3. The pressure transmitter is small in size, light in weight, easy to install, debug and use;


4. The pressure transmitter is a stainless steel fully enclosed casing, which is waterproof;


5. The pressure sensor directly senses the measured liquid level pressure,

and is not affected by the foaming and deposition of the medium.


Main advantages of pressure transmitter

1. The pressure transmitter has the characteristics of reliable operation and stable performance;


2. V/I integrated circuit for pressure transmitter,

less peripheral components, high reliability,

simple and easy maintenance, small size, light weight, easy installation and debugging;


3, aluminum alloy die-casting shell, three-terminal isolation, electrostatic spray protection layer, durable;


4, 4-20mA DC two-wire system signal transmission, strong anti-interference ability, long transmission distance;


5. The pressure transmitter has three indicator heads: LED, LCD and pointer. The on-site reading is very convenient. Can be used to measure viscous, crystalline and corrosive media;


6, pressure transmitter with high accuracy and high stability.

Besides, to the original imported sensor has been corrected by laser,

the comprehensive temperature drift,

and nonlinearity of the whole machine in the operating temperature range,

are finely compensated.


Application of pressure transmitter in various industries

Pressure transmitter is a used sensor in industrial practice.

It is widely used in various industrial self-control environments,

involving water conservancy and hydropower, railway transportation,

intelligent building, production automation, aerospace, military, petrochemical, oil well, electric power, ship. , machine tools, pipelines and many other industries.

The pressure transmitter studio must directly contact the measured medium,

often operating in high temperature, low temperature, corrosion, vibration, shock and other environments.

Whether it can operate at the work site,

depends not only on the quality of the product, but also on the optimization. Engineering design, reasonable model configuration, and proper installation and maintenance. Pressure transmitters are an indispensable key component in the fluid industry. Pressure transmitters are mainly used in the following areas:


1. Petroleum, petrochemical, chemical, and throttling devices provide accurate flow measurement and control. It can measure the pressure and level of pipes and tanks.


2. Power, city gas,

and other company businesses need high stability and high precision measurement.


Third, pulp and paper, used in places requiring chemical-resistant liquids, corrosion-resistant liquids.


4. Steel, non-ferrous metals, ceramics, used for furnace pressure measurement and other places requiring high stability, high-precision measurement, etc., used in places where stable measurement is required under strict control (temperature, humidity, etc.).


5. Machinery and shipbuilding are used to strictly control the places,

where high-precision conditions are required for stable measurement.


In general, pressure transmitters are primarily used to measure the pressure,

and level of the media.

In our industrial production, the application is very extensive.


Xi'an Huaheng Instrument specializes in the production of pressure transmitters,

using imported high-quality diffusion silicon and ceramic pressure sensors as sensitive components,

using dedicated integrated modules, fine temperature, zero point, full-range,

and nonlinear compensation to achieve liquid, gas, steam, etc.

Accurate measurement and transmission of media pressure changes.

Realize the ideal monitoring of pressure medium changes in various places in industrial,,

and mining enterprises,

research institutes and other departments.


Application of pressure transmitter in various industries

How to select Pressure transmitter?

1. According to the type of pressure to be measured

Pressure types include gauge pressure, absolute pressure, and differential pressure.

Gauge pressure refers to the pressure based on the atmosphere,

less than or greater than atmospheric pressure;

absolute pressure refers to the absolute pressure zero as the benchmark,

higher than the absolute pressure;

differential pressure refers to the difference between the two pressures.


2. According to the measured pressure range

In general, the actual measured pressure is selected as 80% of the measurement range.


Consider the largest pressure of the system.

In general,

the pressure transmitter pressure range should be at a largest,

of 1.5 times the largest system pressure.

Some water pressure and process control, with pressure spikes or continuous pulses. These spikes may reach 5 or even 10 times the "largest" pressure, which may cause damage to the transmitter. Continuous high-voltage pulses that approach,

or exceed the transmitter's largest rated pressure,

reduce the useful life of the transmitter. Yet, increasing the transmitter's rated pressure will sacrifice the resolution of the transmitter. A buffer can be used in the system to attenuate spikes, which can slow down the sensor's response.


Pressure transmitters are designed to withstand largest pressure,

in 200 million cycles without degrading performance.

A compromise solution between system performance

and transmitter life can be found when selecting a transmitter.



3. According to the measured medium

According to the different measurement media,

it can be divided into dry gas, gas liquid,

strong corrosive liquid, viscous liquid, high temperature gas liquid, etc.

According to the correct selection of different media,

it is beneficial to extend the service life of the transmitter.


4. According to the maximum overload of the system

The maximum overload of the system,

should be less than the overload protection limit of the transmitter,

otherwise it will affect the service life of the transmitter,

or even damage the transmitter. Usually the pressure overload of the pressure transmitter is twice the full scale.


5. Accuracy level according to need

The measurement error of the transmitter is divided according to the accuracy level.

Different accuracy corresponds to different basic error limits

(expressed as the percentage of full-scale output).

In practical applications,

the selection is based on the control requirements of the measurement error,

and by the principle of economic use.


6. According to the system operating temperature range

The temperature of the measuring medium should be

within the working temperature range of the transmitter.

If it is used over temperature,

it will cause large measurement error and affect the service life of the transmitter. In the production process of the pressure transmitter, the temperature will be affected.

Measure and compensate to ensure that the measurement error,.

due to temperature is within the accuracy level required.

In the case of high temperature,

you can consider the choice of high temperature pressure transmitter,

or the installation of condensing tubes, radiators,

and other auxiliary cooling measures.


7. Depending on the compatibility of the measuring medium with the contact material

In some measurement applications, the measuring medium is corrosive.

In this case, materials compatible with the measuring medium,

or special processing must be used to ensure that the transmitter is not damaged.


8. According to the pressure interface form

A threaded connection (M20 x 1.5) is usually used as the standard interface.

9. According to the power supply and output signal

Usually the pressure transmitter is powered by a DC power supply,

and offers a variety of output signal options, including 4 to 20 mA. DC;, 0 ~ 5V. DC, 1 ~ 5V. DC, 0 ~ 10mA. DC, etc., can have 232 or 485 digital output.


10. According to the working environment of the site and other

Whether there is vibration or electromagnetic interference, etc.

Relevant information should be provided for selection to take appropriate action.

In the selection, other electrical connections, etc.

can also be considered on a case-by-case basis.



How do you calibrate a pressure transmitter?

Pressure transmitter calibration

1. Verification of basic error


(1) Close the positive and negative pressure valves of the pressure piping,

open the balancing valve, and connect the calibration circuit.

(2) Remove the positive and negative side exhaust plugs;

use air to blow the residual liquid in the positive and negative pressure chambers,

from the exhaust plug through the venting plug,

and turn on the power after checking and confirming.


(3) The pressure gauge is not pressurized,

the high and low pressure chambers are at zero atmosphere, and the output should be 4 mA. If the zero offset, you can adjust the zero potentiometer.


(4) After adjusting the zero position, pressurize to the upper limit of the range with a pressure gauge. The output should be 20 mA. If the full scale is offset, adjust the full-scale potentiometer.


(5) Repeat steps (1) and (2) until the output is 4 mA and the full-scale pressure output is 20 mA.


(6) The verification point will include not less than 5 points,

including the upper and lower limits.

The verification points should be distributed over the entire measurement range,

that is, the verification points are on the 0%, 25%, 50%, 75%, and 100% of the range.


(7) At the time of detection, the pressure signal is input from the lower limit value to each point check point,

and the output value is read and recorded up to the upper limit;

then the pressure signal is changed in the reverse direction,

to each verification point, and the output value is read and recorded.

Up to the lower limit. The test of such an up and down stroke is taken as one cycle. 3 cycles are required for doubt and arbitration


Verification.


(8) The basic error of the transmitter is calculated according to the following formula: △A=Ad-As:


△A——The basic error value of each test point of the transmitter (in absolute error mode, mA or Kpa);

Ad——the actual output value (mA or Kpa) of each test point of the transmitter's upper stroke or lower stroke;

As——The theoretical output value (mA or Kpa) of each test point of the transmitter.


2. Verification of return error

Verifying the return error of the transmitter,

is performed with the basic error of the verification transmitter.

The return error is calculated according to the following formula:

△h=│Ad1-Ad2│

where:

△h——return error value (in absolute error mode, mA or Kpa);

Ad1, Ad2——representing each verification point up and down.

The actual output value of the stroke is taken as the arithmetic mean (mA or Kpa) for each of the three cycles.


3. The basic error and return error,

should meet the requirements of the respective tolerances of the transmitter.

When the allowable error is expressed in absolute error mode,

it can be calculated according to the following formula: △=±Am·C%


△——allowable error (mA or Kpa) expressed in absolute error mode;


Am——the output range (mA or Kpa) specified by the transmitter;


How to install Pressure transmitters

Read the product sample and instruction manual before installing the pressure transmitter.

The pressure interface,

should not leak during installation to ensure the correct range and wiring.

The outer casing of the pressure sensor and transmitter should be grounded. The signal cable should not be mixed with the power cable. Strong electromagnetic interference should be avoided around the sensor and transmitter.

Pressure transmitter installation:

There are several types of pressure transmitters installed. Currently, there are: 


(1) Direct pipe installation, which is simple in installation and less in material.

Direct pipe installation pressure transmitter

Direct pipe installation pressure transmitter


(2) Flange mounting


 Flange mounting  of pressure transmitter

Flange installation is used for liquid level measurement,

and the liquid level is measured by the static pressure of the liquid.


(3) Bracket installation (tube-mounted flat bracket)

image

Most of them adopt this type of installation, which is easy to install and maintain.

In the past, the instrument box was used as a protection pressure transmitter,

to protect it from dust and rain.

Yet, the pressure transmitter is now well protected, and the protection level is IP65.

The working environment temperature is -40 to +75 °C,

which is resistant to vibration, dust and rain, and is maintenance-free for 5 years.


Routine maintenance of pressure transmitters

Pressure (differential pressure) transmitter is divided into:

pressure transmitter, absolute pressure transmitter,

differential pressure transmitter,

low, medium and high differential pressure transmitter,

high static pressure change according to the pressure of the measured medium.

The transmitter, etc., converts the pressure

(differential pressure) signal into a standard electrical signal (4-20 mA),

for remote transmission, and can measure pressure, flow, and liquid level.


Daily maintenance and regular maintenance of pressure transmitters:


2.1.1 Perform a sanitary cleaning once a week to keep the transmitter and its accessories clean;


2.1.2 Check the pressure piping and valve joints for leaks once a week. If there is leakage, it should be treated as soon as possible.


2.1.3 Monthly inspection of the transmitter parts intact, no serious corrosion, damage;

nameplate, logo clear and correct;

fasteners should not be loose, the connector is in good contact, the terminal wiring is firm;


2.1.4 Check the on-site measurement line once a month,

including whether the input and output circuits are intact,

whether the line is disconnected, short-circuited, and whether the insulation is reliable.


2.1.5 Check the accuracy of the zero point and display value of the instrument every month. The zero point and display value of the transmitter are accurate and true.


2.1.6 Calibrate regularly according to the transmitter calibration cycle. 2.1.7 Periodically discharge, condense or vent the transmitter.


2.1.8 Periodically fill the isolation fluid for the transmitter,

with the isolation fluid from the source line or measuring component. 2.1.9 Regularly purging the pressure guiding tube of the easily blocked medium. 2.2 When the transmitter is deactivated for a long time, the door should be closed once.


2.3 When the transmitter is running, its housing must be well grounded.

The transmitter used to protect the system,

should have measures to prevent power failure,

short circuit, or open circuit.


2.4 In the winter season,

the instrument should be inspected for the source,

and pipeline insulation and heat supply,

so to avoid the damage of the source pipeline or the measuring component of the transmitter

(the climate in the south is high, generally it is not necessary to keep the pipeline insulated).


2.5 Develop a detailed sewage disposal plan and discharge regularly


The main discharges are mainly for instruments that are easy to condense,

easy to crystallize, and easy to deposit. This work should be tailored to local conditions.


(1), sewage objects


The sewage is mainly for differential pressure transmitters and pressure transmitters.

The measurement medium contains dust,

grease, fine particles and the like deposited in the pressure guiding tube

(or deposited in the pressure regulating valve),

which directly or indirectly affects the measurement.

The discharge cycle can be planned by the instrumentation staff,

according to the practice and executed regularly.


(2), regular discharge should pay attention to:


a. Before the sewage is discharged,

it must be contacted by the craftsman to get the approval of the craftsman.


b. Before the flow or pressure regulation system discharges the sewage,

it should be automatically switched to manual,

to ensure that the opening of the regulating valve does not change.


c. For the differential pressure transmitter,

the three-valve positive and negative pressure-receiving valve is closed,

before the sewage is discharged.


d. Place the container under the sewage valve,

and slowly open the positive and negative pressure guiding pipe drain valve,

to prevent materials, and dirt from entering the container,

to prevent the material from being directly discharged into the trench. Otherwise, it will pollute the environment and cause waste. e. Due to the poor quality of the valve, the switch of the sewage valve will not be dead after several times.

The emergency measure is to add a blind plate,

to ensure that the drain valve is not leaking, so as not to affect the measurement accuracy.


f. Open the three-valve positive and negative pressure-receiving valve,

loosen the sewage (exhaust) screw,

on the body of the differential pressure transmitter for sewage discharge,

and complete the tightening of the screw.


g. Observe the on-site indicating instrument until the output is normal. If the system is adjusted, it will be switched manually and automatically.


What is the difference between pressure transmitter and differential pressure transmitter?



The difference between pressure transmitter and differential pressure transmitter


The pressure transmitter is composed of a load cell sensor (also called a pressure sensor),

an amplifying circuit and a supporting structural member.

It can convert the physical pressure parameter changes,

such as gas and liquid,

measured by the load cell sensor into electrical signals (such as 4~20mA, etc.),

to provide indications, alarms, recorders, conditioners,

and other secondary instruments for display, sign and Change.


QQ截图20190118141354_meitu_1


The difference between pressure transmitter and differential pressure transmitter


Pressure transmitters are used to measure the level,

density and pressure of liquids, gases or vapors and then converted to a 4-20 mA signal output.


Differential pressure transmitters are also called differential pressure transmitters.

They are mainly composed of load cell sensors,

module circuits, display heads, case and process connectors.

It can convert the received gas, liquid and other pressure difference signals,

into standard current,

and voltage signals to supply secondary instruments such as:

alarms, recorders, regulators, etc. for measurement, sign and process change.


The measurement principle of the differential pressure transmitter is that:

the process pressure and the reference pressure respectively.

act on the two ends of the integrated silicon pressure sensitive component,

and the differential pressure causes the silicon wafer to be deformed

(the displacement is small, only μm level),

so that the silicon wafer is used.

A fully dynamic Wheatstone bridge,

made of semiconductor technology,

outputs an mV-level voltage signal,

proportional to the pressure driven by an external current source.

Due to the excellent strength of the silicon material,

the linearity and variation index of the output signal are high.

In operation, the differential pressure transmitter converts the measured physical quantity,

into a mV-level voltage signal,

and sends it to a differential amplifier with a high amplification factor,

that cancels the temperature drift.

The amplified signal is converted into a corresponding current signal by voltage-current conversion,

and then subjected to nonlinear correction, and a standard current-voltage signal,

corresponding to the input pressure is generated.


The above is the simple difference,

between the differential pressure transmitter and the pressure transmitter in the working principle.


A pressure transmitter converts a practical pressure value,

into a regulated electrical signal output.

The differential pressure transmitter compares the pressure difference between the two pressure values,

and converts this difference into a canonical signal output

(practice is to do subtraction and then output the difference).


The differential pressure transmitter measures the difference in pressure,

between two (inside the container) gas or liquid as a relative amount.

The pressure transmitter measures the pressure of a single

(inside the container) gas or liquid in an absolute amount.


The pressure transmitter converts the actual pressure value,

into a regulated electrical signal (eg 0-10 VDC) output,

and the differential pressure transmitter,

compares the pressure difference between the two pressure values,

converting this difference into a specification Signal output

(practice is to do subtraction, then output difference).

The differential pressure transmitter has two interfaces,

measuring the differential pressure between the two ports,

and the pressure transmitter is an interface, measuring gauge pressure or absolute pressure.


Simply put, the pressure transmitter measures the pressure at one point.

The differential pressure transmitter measures the pressure difference between two points

(high pressure side and low pressure side).

If the low pressure side is directly connected to the atmosphere,

the differential pressure transmitter can also be used as a pressure transmitter.



Pressure transducer diagram

Pressure transducer


Pressure transducer


Pressure transducer



 Read more:   

 Common Pressure Transmitter Failures And Troubleshooting

Fault Diagnosis And Analysis Of Intelligent Pressure Transmitter

How to improve the service life of smart pressure transmitters

How to select the model of pressure transmitter

The Working Principle Of The Pressure Transmitter

What Is An Absolute Pressure Sensor/Transmitter?