Вопросы, которые задают на интервью младшим механикам
Давайте проверим Ваши знания и ответим на 3 вопроса средней сложности, которые могут попасться на интервью.
1) Что такое DP transmitter и для чего он предназначен?
Differential pressure transmitter (исходя из названия) измеряет давление в нижней и верхней точках котла. При изменении давления – запускает насос подкачки воды. Смотрим картинки 1 и 2 ⬇️.
2) Почему важно держать средний уровень воды в Sight glass опреснителя?
Уровень в sight glass – это уровень нашего “brine” – излишка очень солёной воды (рассола / ропы), который с помощью эжектора откачивается за борт. Слишком высокий уровень говорит о низкой эффективности, а слишком низкий – о малом количестве воды в испарителе и слишком высокой эффертивности.
3) Что такое и от чего зависит “interface” в сепараторах?
“Interface” – это граница между водяным затвором и рабочей жидкостью сепаратора (масло/топливо). На него очень легко влияют изменения плотности, вязкости, температуры и текучести.
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Давайте поговорим о том, что это за тест и как его производить. Мало кто знает, что Аварийный дизель-генератор нужно регулярно тестировать и брать под.
ADNOC evaluation for Jack-Up barge – кому-то может показаться это обременительным и отбить охоту вообще связываться с этим процессом. Но если разобраться, что он из.
В этой статье я хочу раскрыть различия между Self Propelled JackUp barge, AHTS DP2 и General Cargo, исходя из моего опыта работы капитаном на данных.
Планирование грузовых операций на танкере – задача не из простых. Старпому нужно учесть множество факторов: Какой груз мы будем вести? Какой рейс будем совершать? Сколько.
Basics of Differential Pressure Transmitters
One of the most common, and most useful, pressure measuring instruments in industry is the differential pressure transmitter. This device senses the difference in pressure between two ports and outputs a signal representing that pressure in relation to a calibrated range.
Differential pressure transmitters may be based on any of the previously discussed pressure-sensing technologies, so this section focuses on application rather than theory.
DP transmitter construction and behavior
Differential pressure transmitters constructed for industrial measurement applications typically consist of a strong (forged metal) body housing the sensing element(s), topped by a compartment housing the mechanical and/or electronic components necessary to translate the sensed pressure into a standard instrumentation signal (e.g. 3-15 PSI, 4-20 mA, digital fieldbus codes):
Two models of electronic differential pressure transmitter appear in the following photographs, the Rosemount model 1151 (left) and model 3051 (right):
Two more models of electronic differential pressure transmitter are shown in the next photograph, the Yokogawa EJA110 (left) and the Foxboro IDP10 (right):
pressure-sensing element is housed in the bottom half of the device (the forged-steel structure) while the electronics are housed in the top half (the colored, round, cast-aluminum structure).
Regardless of make or model, every differential pressure (“DP”, “d/p”, or ΔP) transmitter has two pressure ports to sense different process fluid pressures.
These ports typically have 1/4 inch female NPT threads for convenient connection to the process. One of these ports is labeled “high” and the other is labeled “low”. This labeling does not necessarily mean that the “high” port must always be at a greater pressure than the “low” port.
What these labels represent is the effect any increasing fluid pressure applied to that port will have on the direction of the output signal’s change.
The most common sensing element used by modern DP transmitters is the diaphragm. One side of this diaphragm receives process fluid pressure from the “high” port, while the other receives process fluid pressure from the “low” port.
Any difference of pressure between the two ports causes the diaphragm to flex from its normal resting (center) position. This flexing is then translated into an output signal by any number of different technologies, depending on the manufacturer and model of the transmitter:
The concept of differential pressure instrument port labeling is very similar to the “inverting” and “noninverting” labels applied to operational amplifier input terminals:
Similarly, the “H” and “L” labels on a DP transmitter’s ports do not imply magnitude of input pressures; i.e. it is not as though the “H” port’s pressure must be greater than the “L” port’s pressure.
These symbols merely represent the different effects on the output signal resulting from pressure applied to each port. An increasing pressure applied to the “high” port of a DP transmitter will drive the output signal to a greater level (up), while an increasing pressure applied to the “low” port of a DP transmitter will drive the output signal to a lesser level (down):
The ability to arbitrarily connect a DP transmitter to a process in such a way that it is either direct-acting or reverse-acting is a great advantage.
In the world of electronics, we refer to the ability of a differential voltage sensor (such as an operational amplifier) to sense small differences in voltage while ignoring large potentials measured with reference to ground by the phrase common-mode rejection.
An ideal operational amplifier completely ignores the amount of voltage common to both input terminals, responding only to the difference in voltage between those terminals. This is precisely what a well-designed DP instrument does, except with fluid pressure instead of electrical voltage.
A DP instrument ignores gauge pressure common to both ports, while responding only to differences in pressure between those two ports. Stated in other words, a differential pressure instrument (ideally) responds only to differential pressure while ignoring common-mode pressure.
differential pressure transmitter together using pipe or tube, then expose both ports simultaneously to a source of fluid pressure such as pressurized air from an air compressor. If the transmitter is in good working order, it should continue to register zero differential pressure even as we vary the amount of static pressure applied to both ports.
So long as the applied pressures to each port are equal, the transmitter’s sensing diaphragm should experience zero net force pushing left or right. All force applied to the diaphragm from the “high” port’s fluid pressure should be precisely countered (canceled) by force applied to the diaphragm from the “low” port’s fluid pressure.
An electrical analogy to this would be connecting both red and block test leads of a voltmeter to a common point in an electrical circuit, then varying the amount of voltage between that point and earth ground. Since the voltmeter only registers differences of potential between its test leads, and those test leads are now electrically common to one another, the magnitude of common-mode voltage between that one point of the circuit and earth ground is irrelevant from the perspective of the voltmeter:
In each case the differential measurement device rejects the common-mode value, registering only the amount of difference (zero) between its sensing points.
The same common-mode rejection principle reveals itself in more complex fluid and electrical circuits.
Consider the case of a DP transmitter and a voltmeter, both used to measure differential quantities in a “divider” circuit :
In each case the differential measurement device responds only to the difference between the two measurement points, rejecting the common-mode value (97.5 PSI for the pressure transmitter, 97.5 volts for the voltmeter).
Just to make things interesting in this example, the “high” side of each measuring instrument connects to the point of lesser value, such that the measured difference is a negative quantity.
This nameplate tells us that the transmitter has a calibrated differential pressure range of 50” H2O (50 inches water column, which is only about 1.8 PSI).
However, the nameplate also tells us that the transmitter has a maximum working pressure (MWP) of 1500 PSI. “Working pressure” refers to the amount of gauge pressure common to each port, not the differential pressure between ports.
Taking these figures at face value means this transmitter will register zero (no differential pressure) even if the gauge pressure applied equally to both ports is a full 1500 PSI! In other words, this differential pressure transmitter will reject up to 1500 PSI of common-mode gauge pressure, and respond only to small differences in pressure between the ports (1.8 PSI differential being enough to stimulate the transmitter to full scale output).
Credits : Tony R. Kuphaldt – Creative Commons Attribution 4.0 License
DP Transmitter Interface Level Measurement Principle, Limitations, Selection, Installation, Design & Calibration
The principle of differential pressure level measurement is based on hydrostatic head.
Hydrostatic pressure measurement is the most common means for liquid and interface level measurements. For most applications, differential transmitters are preferred because the range selection is flexible and widely understood.
They are used with open and enclosed vessels. Differential transmitters are usually connected to the side of a vessel or tank with isolation facilities.
Table of Contents
Interface liquid–liquid level calculation example
The differential pressure,
DP = hinterface x g x [ ρ2 – ρ1 ] + ρ1 x g x H (Equation [1])
- At hinterface = 0 then DP = ρ1 x g x H
- At hinterface = H then DP = ρ2 x g x H
Figure – DP measurement
Following the principle, measurement of several interface layers can be considered by staging each interface level measurement. For an interface measurement between two liquids the limitation is derived from Equation [1].
The combination of density difference and the distance between the upper/lower nozzles should result in a minimum DP range of around 30 mbar.
Limitations
If both density values ρ2 and ρ1 are similar, the interface level measurement may nearly not be detected by the transmitter. This depends on the DP range, accuracy and distance between the upper and lower nozzles. This occurs typically for an interface measurement between oil and water the case of presence of “heavy” oil (the oil density value is nearly the same as the water density value).
Selection
Differential pressure measurement could be considered for most applications with liquid–gas or liquid–liquid interface level measurement.
Differential pressure transmitters can be used in severely turbulent, dirty, in presence of foam above the liquid or fouling service with diaphragm seals and capillaries.
Differential pressure transmitter with diaphragm seals and capillaries are preferred. This should be provided with a flushing ring mounted between the process flange and the diaphragm seal.
Capillaries should be specified at the correct length, without the need for coiling excess capillary that is surplus to the run. Capillaries should be protected from damage using a basic channel system, allowing sufficient bend radius for the capillaries.
Diaphragm material should be carefully selected according to the type of fluid (e.g. gold plated in presence of hydrogen).
The use of wet legs with intermediate liquids and zero adjustment implies more complex range calculation and higher maintenance needs. Differential pressure transmitter used without diaphragm seals and capillaries should have block and bleed valve manifolds as a minimum. In vapour or cryogenic services, the dry leg should have a self‐purge.
Figure – DP Impulse lines
Wet leg
If the ‘reference leg’ is filled with a liquid, a permanent zero offset will be created. This offset should be compensated.
The wetted leg liquid should be selected for avoiding the risk of evaporation and leakage.
Figure – DP Level vs density measurement
3. Symmetric and asymmetric capillaries
Differential pressure seal system is typically specified with identical capillary lengths and seal configurations on both the high and low pressure process connections. This type of system is traditionally specified because it compensates for temperature induced errors.
Figure – Process connection with diaphragm
In case there is a risk of freezing liquid in the chamber of the flange adapter/reducer or a high viscosity heat tracing or heating circuit should be considered. Heating medium (steam/oil) should not exceed the fluid boiling point.
Process temperature and ambient temperature should be considered to avoid the fluid boiling or affecting the measurement reaction time (in case of higher fluid viscosity). In a vacuum application this may cause the fluid to reach the boiling point and consequently to blow up the diaphragm and destroy it.
Figure – DP Steam heating facilities
Diaphragm material should be carefully selected according to the fluid properties (e.g. gold plated in presence of hydrogen or subject to hydrogen permeation).
Flange connection should be selected according to the piping/vessel code.
Figure – DP SM or RTJ diaphragm flanges
The inner volume of capillary fluid can affect the measurement accuracy and response time. Capillary with internal 1 mm diameter will minimize the effect of temperature variation but will increase the response time. Capillary with internal 2 mm diameter will decrease the response time but will more affected by the fluid dilatation.
Seal fluids compatibility with the line process fluids should be reviewed to confirm it is suitable and prevent contamination of the process stream (e.g. oxygen service).
In the presence of wax, slurries, clogs flushing rings should be considered. Flushing rings should be fitted with vent and drain facilities. Diaphragm seals should include isolation features to enable maintenance.
Figure – DP capillary protection
The differential pressure transmitter should be mounted below the lowest level to be measured.
The capillary position should avoid any risks of vaporization.
Figure – DP Capillary arrangement
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9 thoughts on “DP Transmitter Interface Level Measurement Principle, Limitations, Selection, Installation, Design & Calibration”
Thanks for this article but i think in case of we have two liquids as per above example liquid -1- & liquid -2- includes Gas as the third type of fluid in the closed tank ,so it is better to use Multi phase Density Meter rather than makes this kind of complexity and the disadvantages of using DP transmitter for measurement of density in terms of Height -Pressure – Specific gravity, why because for a specific application it is important to know exactly the density of liquid -1- and -2- and what about the area called interface or we call it in hydrocarbon products SLOP means here the density is neither for liquid -1- not for liquid -2-
And how we can controls this area so it is better to use the theory of tuning fork principle to measure the density (On Line) this is for single liquid in one closed tank and to use Multi phase density for multi phase liquids despite we will have the interface area or we call it SLOP, also this can be detected by other device, personally i used such application in our pumping station for hydrocarbon products in Iraq and all depots or tank farm Area, we have density on line meter and devise to detect the SLOP product and to avoid any type of contamination between hydrocarbon products carrying on one single line, of course this is via pipe lines and form tanks it is the same idea we can install On line density meter using the principle of tuning fork if we have single liquid and if we have more multi phase density meter is the best solution and i think DP transmitters are the best solution for level measurement and flow as well using square root criteria for flow.
Dear sir
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Use Differential Pressure Transmitter to Measure Liquid Level
Differential Pressure Level transmitter for Continuous tank level measurement.
A liquid level measurement solution that prevents the measured medium from directly acting on the transmitter.itle
In the chemical production, the medium often encounters problems such as impurities, crystal particles or agglomeration. It is easy to block the connecting pipeline. At this time, a flange-type differential pressure transmitter is required.
Silicone oil is filled in the closed system composed of the bellows, capillary tube and measuring chamber as the pressure transmission medium. The measured medium does not enter the capillary tube and the transmitter to avoid blockage.
Differential Pressure Level transmitters are divided into single flange type and double flange type according to their structure.
Only a flange between the container and the transmitter is called a single flange differential pressure transmitter.
As for the closed container whose upper end is isolated from the atmosphere, the upper space and atmospheric pressure are mostly different. Two flanges must be used to guide the liquid and gas phase pressure to the differential pressure transmitter. This is the double flange differential pressure transmitter.
Differential Pressure Level transmitter for open containers
Open tank level measurement means that the tank is open to the atmosphere. Any change in atmospheric pressure will affect the process fluid pressure in the tank. In this liquid level measurement application, the low pressure side of the transmitter can measure the atmospheric pressure. This eliminates the influence of atmospheric pressure on the tank liquid level. The high-pressure side of the transmitter is connected to the tank. Therefore, the actual liquid level in the tank can be measured.
A single flange is used to measure the liquid level of an open tank.
Differential pressure range calculation method: Need to measure the height of the liquid level (unit: m) × acceleration of gravity (9.8) × measured medium density (unit: g/cm3) differential pressure range (unit: KPa).
The selection must know the measurement medium, measuring range, medium temperature, the size and pressure rating of the process connection flange, and the flange standard.
Differential Pressure Level transmitter for closed containers
For airtight containers, the inside is isolated from the atmosphere. When the process fluid fills or empties the tank, the pressure in the tank may change from positive pressure to vacuum. This change in tank pressure will directly affect the measured liquid level unless it is compensated for. This can be done by connecting the low-side pipe of the differential pressure transmitter to the top of the tank. Therefore, when measuring the liquid level of a closed tank, a differential pressure transmitter must be used.
Double flanges are used to measure the liquid level of a closed tank.
The calculation method of the differential pressure range: the height of the liquid level to be measured (unit: m) × acceleration of gravity (9.8) × (the density of the measured medium-the density of the capillary filling liquid) (unit: g/cm3) = differential pressure range (unit: KPa).
The selection must know the measurement medium, measuring range, medium temperature, pressure, capillary length, the size and pressure rating of the process connection flange and the flange standard
If you need to measure river water level, open channel level, etc. The Ultrasonic Liquid Level Sensor can be used for non-contact continuous level monitoring.
Differential pressure level transmitter working principle
When using Differential pressure (DP) level transmitter to measure the liquid level as shown in the figure below.
The measured liquid density in the figure is ρ.
The working medium density in the capillary of the double flange differential pressure transmitter is ρ0.
The measuring range of the measured liquid level is H.
The center distance of the sampling tube of the measured liquid level is h.
It can be seen from the figure that the maximum measurement range of the liquid level △ P = P + —P- = H × ρ × g-h × ρ0 × g.
It can be seen from the formula that the dual-flange differential pressure transmitter should perform negative migration. The migration amount S is h × ρ0 × g. And the installation position of the double flange differential pressure transmitter has no effect on the migration amount and the measurement result.
The dual-flange differential pressure transmitter requires negative migration.
When the measured liquid level is 0, the pressure difference between the positive and negative measurement chambers of the remote differential pressure transmitter is the largest. The output current of the double flange differential pressure transmitter is 4mA.
As the measured liquid level rises, the pressure difference between the positive and negative measurement chambers of the transmitter gradually decreases.
When the measured liquid level rises to the highest Hmax. The pressure difference between the positive and negative measurement chambers of the transmitter is the smallest. The output current of the double flange differential pressure transmitter is 20mA.
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Sino-Inst offers overs 100 DP transmitters for liquid level, pressure, flow, temperature measurement. Differential pressure (dp) level transmitters suit to measeure water and other liquid level.
A wide variety of DP level transmitters are available to you. Such as SMT3151LT Differential pressure level transmitter.
You can also choose from liquid flow meter and pressure transmitters, not specified. We are differential pressure level transmitter suppliers, located in China. The top supplying country is China(Mainland), which supply 100% of DP transmiters respectively.
Wu Peng, born in 1980, is a highly respected and accomplished male engineer with extensive experience in the field of automation. With over 20 years of industry experience, Wu has made significant contributions to both academia and engineering projects.
Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.