Differential pressure (DP) level transmitter is a perfect solution for tank level measurement. Flanges, seal diaphragms, capillaries, and DP transmitters are often used to measure liquid levels.
Differential pressure(DP) level transmitter is often used as a tank level transmitter. The DP transmitter is connected with a stainless steel flange by the capillary. Flange installation. The pressure is sensed by a remote transmission device installed on the container. The pressure is transmitted to the body of the transmitter through the capillary. The transmitter converts the pressure or differential pressure to 4 ～ 20mA. The DC signal is output. It can communicate for the setting and monitoring by cooperating with the HART communicator. Explosion-proof available.
Features of Differential pressure (DP)level transmitter
- The biggest feature of the differential pressure transmitter is that it can be easily installed on existing vessels. It can also be converted into a working tank or container.
- The maintenance of the DP transmitter is easy because it can be isolated from the process by an isolation valve.
- DP transmitter is ideal for liquid level measurement. It can also be used for light mud with an extended diaphragm, which can be installed flush on one side of the container.
- Level measurement via DP transmitter is more cost-effective than other available sensors.
- Since the DP transmitter is far away from the tank for liquid level measurement, it is easy to clean and maintain the tank.
- The detection element takes up almost no space in the container. Instead, only two pressure holes need to be opened in the container wall.
- There is no movable part in the detection part. Installation method, the work is more reliable.
- The weight of the liquid column height per unit area is measured. The change of the measured medium weight will directly affect the measurement result. When the purpose of the measurement is to determine the weight storage of the material in the container. No additional amendments are required.
- The use of flange pressure can solve the liquid level measurement of high viscosity, easy to crystallize, and medium with suspended matter. Evaporation and boiling liquid level can also be measured, but sometimes the error is large.
- The display part of the instrument can usually adopt the general unit in the unit group instrument. No separate design is required.
There are four types of remote transmission devices for remote differential pressure transmitters:
- Flat type
- Thread mounting type
- Flange mounting type
- Extended Diaphragm Seal
Specifications of DP level transmitter
|Liquids, gases and steam
|4-20mA, superimposed Hart protocol, RS485
|All 316L stainless steel
|± 0.2% FS, ± 0.1% FS, ± 0.075% FS (customizable)
|316L, customizable Ha C, tantalum, Monel alloy
|-10 ~ + 70 ℃
|Long-term stability (1 year)
|≤ ± 0.25% FS
|-20 ~ + 100 ℃
|External continuously adjustable
|Less than 0.005% / V of output range
|3.9KG (standard type)
|Less than 0.16cm3
|If the power supply is stable, the load has no effect
Applications of DP level transmitter
The differential pressure liquid level transmitter can prevent the measured medium from directly contacting the sensor diaphragm of the transmitter. It is suitable for the following situations:
- When the measured medium has a corrosive effect on the transmitter connector and sensitive components;
- When the high temperature measured medium needs to be isolated from the transmitter;
- When there are solid suspended solids or high viscosity in the measured medium, it is easy to block the transmitter connector and the pressure chamber;
- When the measured medium is easily cured or crystallized by the pressure tube;
- When changing the measured medium needs to be rinsed and not to be mixed;
- Hygienic conditions must be maintained to prevent pollution. .
- Changing the measured medium requires strict purification of the measuring head
- Suspended liquid or high viscosity medium
- Measurement of sealed pressure vessel.
Read more What is a diaphragm seal?
Differential pressure type level transmitter working principle
Differential pressure (DP) level transmitter is a differential pressure transmitter to prevent the measured medium from directly acting on the transmitter. The differential pressure transmitter uses remote transmission isolation diaphragm contact. The remote transmission differential pressure transmitter (double flange) is composed of a differential pressure transmitter and a welded remote flange with capillary tube. Its working principle is the same as the differential pressure transmitter. Only the pressure transmission path is slightly different. The measurement diaphragm chamber of the transmitter is connected with a stainless steel capillary (tube with a diameter of about 3mm, plus protection) and the channel is several meters to tens of meters. One of the other places will be two (pressure or differential pressure) made into a flange-shaped measuring diaphragm box. The middle is filled with the transfer medium (silicone oil). When using, connect the flange to the device to measure.
Differential pressure transmitter level measurement calculation
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.
Read more about Differential Pressure Transmitter Installation Guide
How to calibrate differential pressure transmitter for level
The differential pressure liquid level transmitter has been calibrated in the range, accuracy, linearity and other parameters according to customer requirements at the factory. And mark the range, accuracy, etc. on the nameplate of the differential pressure liquid level transmitter. As long as the density and other parameters of the measured medium meet the requirements of the nameplate, generally no adjustment is required.
If the customer needs to adjust the range or zero position, please adjust according to the following methods. Assuming that the range of the differential pressure liquid level transmitter is 0 ~ 10 meters:
How to calibrate a differential pressure level transmitter ?
Unscrew the protective cover of the differential pressure liquid level transmitter. It can be adjusted by connecting external standard 24VDC power supply and ammeter (requires accuracy of 0.2% or above).
When there is no liquid in the differential pressure liquid level transmitter. Adjust the zero potentiometer. Make it output current 4mA.
Pressurize the differential pressure liquid level transmitter to full scale (10 meters). Adjust the full-scale resistor. Make it output current 20mA.
Repeat the above steps two or three times until the signal is normal.
Please input 25%, 50% and 75% signals to check the error of the differential pressure liquid level transmitter.
For non-aqueous media. Differential pressure level transmitters are calibrated with water. It should be converted according to the pressure generated by the actual density of the medium. For example, when the medium density is 1.3, the 1.3m water level should be used to calibrate the 1m range.
After adjustment, tighten the protective cover.
The verification cycle of the differential pressure liquid level transmitter is once a year.
HART intelligent differential pressure liquid level transmitter of Sino-Inst instrument can be selected. It is convenient to adjust the range of the differential pressure liquid level transmitter.
Extended reading: How to calibrate HART pressure transmitters
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What is the difference between pressure transmitter and differential pressure transmitter?
The principle of the pressure transmitter is: The medium pressure acts directly on the sensitive diaphragm. A Wheatstone bridge composed of resistors distributed on the sensitive diaphragm. The use of the piezoresistive effect realizes the conversion of pressure into an electrical signal. Amplify the millivolt signal generated by the sensitive element through an electronic circuit into an industrial (such as 4 ~ 20mA, 0 ~ 5V) standard signal. But the pressure transmitter has only one pressure interface.
The principle of a differential pressure transmitter is: a transmitter that measures the pressure difference between the two ends of the transmitter. Output standard signals (such as 4 ~ 20mA, 0 ~ 5V). Differential pressure transmitters are different from general pressure transmitters in that they have two pressure interfaces. Differential pressure transmitters are generally divided into positive pressure end and negative pressure end. H is the positive pressure end and L is the low-pressure end. In general, the pressure at the positive pressure end of the differential pressure transmitter should be greater than the pressure in the negative pressure section to measure. Differential pressure transmitters are used to measure the level, density, and pressure of liquids, gases, and vapors. Then convert it into 4–20mA DC current signal output.
In summary: The fundamental difference between a pressure transmitter and a differential pressure transmitter is that the pressure transmitter can only measure the pressure at one pressure end. The differential pressure transmitter can measure the pressure at two pressure points, and the two pressures are subtracted. The pressure difference at the positive pressure end minus the negative pressure end pressure. Thus, the actual liquid level value is converted.
Sino-Instrument (drurylandetheatre.com) offers over 100 DP transmitters for liquid level, pressure, flow, temperature measurement. Differential pressure (DP) level transmitters suit to measure water and another 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 the liquid flow meters and pressure transmitters, not specified. We are a differential pressure level transmitter supplier, located in China. The top supplying country is China(Mainland), which supply 100% of DP transmitters respectively.
Differential pressure level transmitter is most popular for India, Pakistan, South Africa, The US. The quality is the same as the original premium quality. You can ensure product safety by selecting from our products, including IOS9000, … certification. You can find more information about our SMT3151LT DP Level transmitter, you can refer to our differential pressure level transmitter pdf:
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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.