The DP level transmitter works on the principle that the hydrostatic pressure difference of a liquid is directly proportional to the liquid level height. It calculates the liquid level by measuring the pressure difference of the medium inside the container and outputs a standard electrical signal. The dual-flange capillary structure provides mechanical and thermal isolation, allowing it to handle complex corrosive and high-temperature media in various industrial processes and tank level monitoring applications.
Sino-Inst offers a variety of DP Level Transmitters for industrial pressure measurement. Connection with diaphragm seals. If you have any questions, please contact our sales engineers.
Features
Specifications of DP level transmitter
| Measuring Medium: | Gases, Vapors, Liquids |
| Measuring Range | -100kPa…0~6kPa…7MPa |
| Accuracy: | ±0.075%, ±0.1%, ±0.2% (including linearity, hysteresis, and repeatability from zero point) |
| Stability: | ±0.2%/year |
| Power Supply: | 10–36V DC (24V DC recommended) |
| Reference Accuracy for Range Adjustment: | If TD > 10 (TD = Maximum range / Adjustable range), then: ±(0.075 × TD)% |
| Ambient Temperature: | -40℃ ~ 85℃ |
| Measuring Medium Temperature: | -40℃ ~ 400℃ (higher/lower temperatures can be customized) |
| Storage Temperature: | -40℃ ~ 85℃ |
| Display: | LCD, OLED |
| Display Module Temperature: | -20℃ ~ 70℃ (LCD), -40℃ ~ 80℃ (OLED) |
| Measuring Diaphragm: | 316L, Hastelloy C, Tantalum, Titanium, Nickel, Monel, Duplex Stainless Steel, PFA, Gold Plating |
| Process Connection: | Stainless steel 316L, 304 |
| Filling Fluid: | Silicone oil, fluorinated oil, etc. |
| Transmitter Housing: | Aluminum alloy material, epoxy resin coating on the surface |
| Housing Seal: | Nitrile rubber |
| Nameplate: | Stainless steel 304 |
| Enclosure Protection Rating: | IP67 |
| Explosion Protection Rating: | Exd Ⅱ CT6 Gb, Exia Ⅱ CT6 Ga |
| Measuring Range Limits | Within the upper and lower limits of the range, it can be set arbitrarily, as long as the calibrated range ≥ the set range. It is recommended to choose a range with the lowest possible range ratio to optimize performance. |
| Influence of Mounting Position | Changes in installation position will cause zero point influence, which can be corrected by zero adjustment; there is no range influence. |
| Output | Two-wire 4-20mA, compliant with NAMUR NE43 standard, superimposed digital signal (Hart protocol) |
| Output Signal Limits | Imin (minimum): 3.9mA Imax (maximum) = 21.0mA |
| Alarm Current | Low alarm mode (minimum): 3.9mA High alarm mode (maximum): 21mA (user pre-settable) |
| Default Alarm Current Setting | High alarm mode |
| Fault Warning | If the sensor or circuit fails, the automatic diagnostic function automatically outputs 22.0mA |
| Response Time | Amplifier component damping constant is 0.1s; sensor time constant is 0.1–1.6s, depending on the range and range ratio. Additional adjustable time constant: 0–100s |
| Warm-up Time | <15s |
There are 5 types of remote transmission devices for remote differential pressure transmitters:
- Flat type
- Thread mounting type
- Flange mounting type
- Extended Diaphragm Seal
- Wet legs/Dry legs
Applications of DP level transmitters
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?
DP level transmitter working principle
The differential pressure level transmitter is an instrument that uses the pressure generated by the liquid column to measure the height of the liquid level. When the liquid level changes, the pressure received by the diaphragm at the high-pressure side flange will change accordingly. The differential pressure value calculated by the transmitter will also change accordingly. There is a linear relationship between them.
Normally, the high-pressure side (H side) and the low-pressure side (L side) cannot be installed reversely. Generally, the H side is installed at the lower part of the equipment, and the L side is installed at the higher part of the equipment. Before installation, the flange surface of the equipment should be cleaned and the gasket should not be placed off-center to prevent the diaphragm from being punctured or deformed, causing distortion of the transmitter.
Differential pressure transmitter level measurement calculation
When using a 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
DP level transmitter calibration
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:
- Unscrew the protective cover of the differential pressure liquid level transmitter. It can be adjusted by connecting an 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 potentiometers. Make it output a current of 4mA.
- Pressurize the differential pressure liquid level transmitter to full scale (10 meters). Adjust the full-scale resistor. Make it output a current of 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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Sino-Inst (drurylandetheatre.com) offers over 20 DP transmitters for liquid level, pressure, flow, and density measurement. Differential pressure (DP) level transmitters are suitable for measuring water and other liquid levels.
We are a differential pressure level transmitter supplier, located in China. Our products are widely exported to the United States, Australia, Singapore, Indonesia, etc. You can ensure product safety by selecting from our products, including IOS9000, and… certification.
Of course, in addition to differential pressure transmitters, pressure transmitters can also be used to measure the liquid level in open tanks. If you need to purchase Level Transmitters or have related technical questions, please feel free to contact our sales engineers!
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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.