Hydrostatic pressure senor/transmitter measures the hydrostatic pressure of liquids. Hydrostatic pressure is used to determine liquid level.

Hydrostatic pressure senor measures the level, density, and pressure of liquid, gas, or steam. And then converts it into a 4-20 mA DC signal output. The Hydrostatic pressure transmitter can communicate with the HART communicator intelligently. Use it to set, monitor or form a site monitoring system with the host computer. Use Hydrostatic pressure sensor to measure tanks, processing vessels, headers, pump inlets and others using hydrostatic pressure to determine liquid height. SI3051HP Hydrostatic pressure transmitters, with working Hydrostatic pressure up to 32Mpa.

Sino-Inst offers a variety of Hydrostatic Pressure Transmitter for industrial pressure measurement. If you have any questions, please contact our sales engineers.

Features of Hydrostatic pressure sensor

The Hydrostatic pressure transmitter, is used to measure the liquid level, flow, and pressure of the liquid, gas or steam under high working pressure, and then convert to 4~20mA DC signal output.

high static pressure transmitter
  • The high hydrostatic pressure transmitter can measure differential pressure below 32MPa hydrostatic pressure.
  • With 32MPa working pressure and overload protection.
  • Ensuring reliable application of the transmitter in Hydrostatic pressure systems.

Specifications of Hydrostatic pressure transmiter

Measure Range of Hydrostatic pressure sensor:

Differential pressure: 0-1.3-6790KPa
Hydrostatic pressure: 32MPa

  • Use object: liquid, gas or steam
  • Output signal: 4-20mA dc. Output superimposed HART protocol digital signal (two-wire system)
  • Power source: external power supply 24V dc. Power supply range 12V ~ 45V
  • Installation in dangerous places:
    • Flameproof  ExdIIBT5Gb;(explosion-proof certificate no. :CE16.1163)
    • Intrinsically safe ExiaIICT4/T5/T6Ga;(explosion-proof certificate no. : CE15.2354X) ;
  • Accuracy: ± 0.1%, ±0.2%
  • Stability: ±0.25%/6 months of maximum range
ModelTransmitter type
HPAbsolute pressure transmitter
CodeScale range
CodeOutput form
ELinear output 4-20mAdc
SFLinear/square root output 4-20mAdc +HART signal,,Full function buttons on site
FMODBUS-485 signal
CodeStructural materials
Flange connectorExhaust/Drain valveIsolation diaphragmFilling liquid
22316 Stainless steel316 Stainless steel316 Stainless steelSilicone oil
23316 Stainless steel316 Stainless steelHastelloy CSilicone oil
24316 Stainless steel316 Stainless steelMonelSilicone oil
25316 Stainless steel316 Stainless steelTantalumSilicone oil
33Hastelloy CHastelloy CHastelloy CSilicone oil
35Hastelloy CHastelloy CTantalumSilicone oil
44MonelMonelMonelSilicone oil
CodeShell materialConduit inlet dimensions
ALow copper aluminum alloy polyurethane coatingM20×1.5
BLow copper aluminum alloy polyurethane coating1/2-14 NPT
CStainless steelM20×1.5
DStainless steel1/2-14 NPT
CodePressure connection
L11/4NPT-18 Internal thread(excluding waist joint standard)
L21/2NPT-14 Internal thread
L3M20×1.5 External thread
CodeOptional parts
M4LCD multi – power digital display head
B1Pipe bending bracket
B2Plate bending bracket
B3Pipe mounting bracket
C02M20×1.5 nut and Φ 14 pressure short tube
C121/2NPT-14 external thread and Φ14 pressure short tube
C221/4NPT-18 external thread and Φ14 pressure short tube
C321/4NPT-18 to M20×1.5 external thread
C421/2NPT-14 to M20×1.5 external thread
C431/2NPT-14 to 1/4NPT-18 internal thread
C441/2NPT-14 to 1/2NPT-14 external thread
C451/2NPT-14 to G1/2 external thread
D1The side discharge valve is on the upper part
D2The side discharge valve is on the upper part
X1Oil ban
DaFlameproof ExdIIBT5Gb;(explosion-proof certificate no. : CE16.1163)
FaIntrinsically safe ExiaIICT4/T5/T6Ga;(explosion-proof certificate no. : CE15.2354X)

Hydrostatic Pressure

Hydrostatic pressure is the pressure generated by the weight of the liquid above the measurement point when the liquid is stationary. The height of the liquid column with uniform density is proportional to the hydrostatic pressure. As the weight of the fluid exerting downward force from above increases, the hydrostatic pressure increases in proportion to the depth measured from the surface.

If the fluid is inside the container, the depth of the object placed in the fluid can be measured.
The hydrostatic characteristics of a liquid are not constant, and the main factors affecting it are the density and local gravity of the liquid. In order to determine the hydrostatic pressure of a particular liquid, both quantities need to be known.

The deeper an object is placed in a fluid, the greater the pressure it bears. This is because the weight of the fluid is higher than its weight. Due to the weight of the fluid, the denser the fluid above it, the greater the pressure on the submerged object.

Measuring principle

The pressure in the liquid increases as the filling height increases. The hydrostatic pressure is transmitted to the measuring unit through the stainless steel diaphragm. Bubbling, accumulation of liquids, fluctuating electrical characteristics, and container design will not affect the measured value.

Formula for calculating hydrostatic pressure

The formula for calculating the hydrostatic pressure of a column of liquid is:

Phyd = h.ρ.g

Prel = h.ρ.g

Pabs = h.ρ.g + Patm

Phyd = Hydrostatic Pressure (Pa)
Prel = Relative Pressure (Pa)
Pabs = Absolute Pressure (Pa)
Patm = Atmospheric Pressure (Pa)
h = Liquid Height (m)
ρ = Liquid Density (kg/m3)
g = Local Gravity (m/s2)

The above calculation formula is also the working principle of hydrostatic liquid level sensor.

What is a Hydrostatic pressure sensor?

The hydrostatic pressure sensor measures the hydrostatic pressure applied by the hydrostatic head. Output 4-20mA.
Use a hydrostatic pressure transmitter to measure the storage tank and pump inlet. And other applications where hydrostatic pressure is used to determine the liquid level.

Hydrostatic Pressure Sensors for liquid level measurement

There are various methods and techniques for measuring fluid level using hydrostatic pressure sensors. Depending on the installation, they all have advantages and disadvantages. Hydrostatic pressure measurement is an accurate and convenient technique for determining fluid height or volume.
Let’s take a look at each according to the installation location of the hydrostatic pressure sensor.

Externally mounted type

Image source: https://www.yourlevelexperts.com/zh-hant/product/hydrostatic-pressure/

The Hydrostatic pressure liquid level sensor can be installed to the outside of the container through threads or flange fittings. If necessary, capillaries can also be used.

Submersible type

Picture source: network picture

If the externally mounted sensor is not available, a submersible pressure sensor can be used. The electrical connection with IP68 rating is suitable for long-term permanent immersion. The electronic equipment of the sensor can be protected from the external environment.

Remote Diaphragm Seal Pressure Transmitter
SMT3151LT Pressure Level Transmitter
SMT3151LT Pressure Level Transmitter
DP type level transmitter
Submersible Level Transmitter
Hydrostatic Level Sensor
Submersible Pressure Transducer
Magnetostrictive level sensor
Magnetostrictive level transmitter

Hydrostatic pressure transmitter fault debugging steps:

How to debug the fault of Hydrostatic pressure transmitter

Total Time: 30 minutes

Check the power supply

Check if the power supply of the differential pressure transmitter is reversed, and whether the positive, and negative poles of the power supply are connected correctly.

Measure the power supply

Measure the power supply of the transmitter, whether there is 24V DC voltage. It must ensure that the power supply voltage to the transmitter is ≥12V
(that is, the voltage of the transmitter power input terminal is ≥12V).
If there is no power supply, check whether the circuit is disconnected, whether the instrument is selected incorrectly (input impedance should be ≤250Ω), and so on.

Check the display meter

If the pressure transmitter is equipped with a meter head, it is necessary to check whether the dislay meter is damaged. You can short-circuit the two wires of the meter head first. If it is normal after a short circuited, it means the head is damaged.
If the meter head is damaged, Then you need to change the header.

Check the current

If there is a problem with the differential pressure transmitter, connect the ammeter to the 24V power supply circuit to check if the current is normal.
If it is normal, the transmitter is normal. In this case, check if other instruments in the loop are normal.

Connect the power supply

Connect the power supply to the transmitter power input terminal, and connect the power cable to the power supply wiring port.
If you still have any question with the selection, application, and use of pressure transmitters, you can just contact our engineer today.


Why is liquid level measurement by hydrostatic pressure?

Hydrostatic level measurement is a very simple and reliable method of measuring levels. Lower or install the submersible pressure transmitter or standard pressure transmitter to a specific depth (zero level). The transmitter then measures the pressure caused by the weight of the liquid directly on top of it. The pressure sensor does not measure the complete volume in the tank above it, but only the vertical liquid column above it. Therefore, the hydrostatic level measurement is completely unaffected by the shape of the reservoir or container, and the level is measured only by the weight of the liquid column above it. If the liquid and its specific gravity are known, the pressure measurement can be calculated as the distance from the zero level where the emitter is located to the surface of the liquid.
Contrary to most non-contact level measurement techniques, hydrostatic level transmitters not only allow the current height of the surface to be measured. It allows monitoring the horizontal change of any selected reference point in the medium, anywhere between the bottom of the resource and its surface. Because the hydrostatic level gauge transmitter is always installed below the surface level. Therefore, the hydrostatic level transmitter is not subject to any interference from the liquid surface. Effects such as overflow, overflow or overflow. Because their installation points become a reference to zero-meter or zero-foot levels, they can analyze and monitor resource levels at unknown depths. Examples of these resources are underground water reservoirs, aquifers, rivers and lakes. Because of all these resources, the surface level may vary greatly.

Submersible pressure transmitter and standard pressure transmitter?

First, you must decide which type of product you want to use. If you have a barrier-free tank, if you do n’t mind having threaded holes in the bottom or side walls of the tank, you should use a standard pressure transmitter. But if you have an underground water reservoir, an underground water tank or tank that you do n’t want to weaken with threaded holes, you should use a submersible pressure transmitter. The probe descends from the top of the water tank or pool into the medium.

How to choose the product suitable for your static pressure level meter measurement?

Once you decide whether to use a standard pressure transmitter or a submersible pressure transmitter, for most applications, you only need to define three to four simple things.
Pressure connection (only if it is a standard transmitter mounted on the side), measuring range, accuracy and electrical connection. The pressure connection should be suitable for the threaded hole in the tank. The measurement range should be selected according to the level you measure in the application. If it is an independent water tank, you will know the height of the water tank. If it is an underground water tank or reservoir, you need to determine the depth of the horizontal probe and select the corresponding measurement range. Remember, a 10 meter water column corresponds to about 1.000 mbar (1 bar) or 14.5 psi.
Select the accuracy according to your application needs. The standard accuracy <0.5% will give you a possible larger error. 5 millimeters per meter level, and higher accuracy variants of <0.1% will be as accurate as greater accuracy. 1 mm level per meter.
Select electrical connection. If you have a standard pressure transmitter, you are free to choose the connector (such as M12 or DINA) or cable socket. When choosing a submersible pressure transmitter, you must always use cables. If your transmitter has a cable connection, you need to select the appropriate length to allow wiring from the transmitter to the control system. And when using the submersible pressure transmitter, allow immersion length.

How to install and set the hydrostatic level transmitter?

After defining and ordering the pressure transmitter, you can install and set up the hydrostatic level gauge measurement system.
If you choose a submersible pressure transmitter, you must lower the device into the medium via a cable. Until you reach the bottom of the tank, reservoir or underground resource. Or until the required zero level is reached. Then, run the cable from the oil tank or water tank to the control system. And connect the level probe to the PLC accordingly.
If you have turbulent media, you should use an extra tank weight to stabilize the level probe in the media to obtain a stable pressure reading. To prevent the cable from any mechanical damage, you can use a cable clamp to fix the cable on top of the water tank. Or fix it along the way when connecting the cable to the control system.
If you choose a standard pressure transmitter, simply screw the transmitter into the threaded hole on the bottom or side of the tank. Then, connect the transmitter to the PLC with the appropriate cable connector. Or if the cable connection has been selected, connect the transmitter directly to the control system.

How to improve the accuracy of static pressure liquid level measurement?

When you set up a hydrostatic level gauge measurement system, you must be aware that liquid level measurement is affected by the specific gravity of the medium and the temperature of the medium, which will also affect the specific gravity of the medium.
If the specific composition of the medium changes, the specific gravity of the medium may be unstable. If you use, for example, wastewater or brine, higher pollutants or salt may increase the specific gravity of the medium. Therefore, your hydrostatic pressure will show a higher reading. So you will calculate the increase in level, and the actual level may actually be lower than your calculation. If you do not see changes in the composition of the medium, for example, you are always measuring the same specific medium (such as diesel), you can ignore the reason for the change in specific gravity through different mediums.
However, as the temperature of the medium changes, the specific gravity will also change. If the temperature increases, the specific gravity of the medium will decrease and the level will increase. But hydrostatic pressure measurement may not accurately reflect this level change. Depending on the shape of the tank or basin, the performance of pressure may be very different from the increase in level caused by temperature changes. It can indicate the decrease of the level (if the tank expands upwards) and display the correct level. Or even show an excessively proportional increase in level (if the tank shape narrows towards the top). When the density increases as the ambient temperature decreases, these effects are reversed.
In order to improve the accuracy of the static level measurement, you must compensate for temperature effects and changes in the specific gravity of the medium.

How to compensate the temperature effect in the static pressure liquid level measurement?

We know that the specific gravity changes with the temperature of the medium. However, if we know how the density changes as the temperature increases or decreases, it is easy to compensate for the effect of temperature on the medium. For example, by using a standard table of media, the specific gravity of each temperature is indicated.
A simple and economical additional sensor. Such as Pt100 temperature probe. Even the integrated temperature sensor in the pressure transmitter. Can provide you with the required temperature measurement. If you know the temperature characteristics of the medium and how to change its specific gravity, you can easily compensate for these effects in the control system. And use the appropriate specific gravity to correct the liquid level calculation according to the standard table.

How to deal with steam, foam, dust, spider web, accumulation and other disturbances?

The answer to this question is simple. Unlike many non-contact liquid level measurement techniques, hydrostatic level gauge measurements are very tolerant of interference.
Submersible or standard pressure transmitters are positioned in direct contact with the medium at measurement points below the surface level. Therefore, they are not affected by any interference above the surface level. For example, foam, dust, water splashes, or spider webs can interfere with the accurate measurement of ultrasound or radar equipment.
Even if the technology is in direct contact with the medium, accumulation, pollution, particles, etc. will not interfere with the sensor. As long as these disturbances are not allowed to dry up on the sensor. Therefore, the sensor is always wetted by the medium. The medium and any accumulation will transfer the hydrostatic pressure to the pressure sensor. If the tank or sink is emptied and allowed to dry on the pressure sensor. You can use cloth or rinse with water. For easy cleaning during planned maintenance.
For these reasons, hydrostatic level gauge measurement is one of the more reliable techniques you can find on the market.

How to monitor volume through static pressure level measurement?

Usually, the water level is measured by hydrostatic pressure measurement. The real goal is to monitor the volume of the medium in the water tank or pool. Because the hydrostatic pressure is not affected by the shape of the container. Therefore, it is not affected by its volume. Therefore, the volume must be calculated in the control system based on the measured current level.
In order to calculate the volume of the container, its shape must be programmed into the control system by using a so-called tank linearization table. It’s basically a simple table. It contains a corresponding set of volumes corresponding to different filling levels of the tank. Control systems usually use linear functions to calculate the volume of any measured hydrostatic pressure.

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