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In current designs for measuring liquid levels in oil tank farms, magnetic flap level gauges are quite popular. While magnetic flap level gauges offer high precision, they are also expensive, and their installation and maintenance are rather complicated. Differential pressure type level detectors are widely used in sealed vessels such as boiler drums, but their measurement results do not represent the actual liquid level; therefore, they are rarely used in the design of oil tank level measurement systems. In fact, the exact liquid level in oil storage tanks is not that important; what users really need to know is not the level itself, but rather the actual amount of oil in the tank, which can be determined by measuring the liquid level. Thanks to its reliable stability, the SMT3151 differential pressure and high-pressure transmitter plays a crucial role in the design of systems for measuring liquid levels in oil storage tanks. As the name implies, the SMT3151 differential pressure and high-pressure transmitter measures pressure differences, namely ΔP = ρgΔh. Since oil tanks are usually cylindrical, the area S of their circular cross-section remains constant. Therefore, the weight G = ΔP·S = ρgΔh·S; with S being constant, G is directly proportional to ΔP. In practical applications: In the design for measuring the liquid level in oil tanks in oil depots, using the SMT3151 differential pressure and high-static-pressure transmitters, a liquid level alarm system is installed at the top of the tanks as a safeguard to prevent the oil from overflowing, serving as a double layer of protection. In the application, since the measured value is given in tons directly, regardless of the type of oil stored in the tank, the value displayed on the secondary meter represents the tons of oil present in the tank, eliminating the need to determine the density for conversion. Generally, the transfer of oil products in and out of storage is carried out using pumps, with flow measurement being done via elliptical gear flow meters. Due to the limited accuracy of these flow meters, which is at most 0.2 grade, it is also necessary to measure the density in order to make accurate calculations. The results obtained using the SMT3151 differential pressure and high-static-pressure transmitters can sometimes differ, leading to disputes over measurements. Now, since the measurement results for oil tanks are given in tons, with an accuracy level of up to 0.2 or even 0.1, the measurement results are more accurate compared to volumetric flowmeters. Although when a small quantity of oil is received or dispatched, the absolute error in the measurement is relatively large due to resolution limitations, when a large volume of oil is handled, its high precision and low relative error are unmatched by other measurement methods, making it particularly suitable for monthly, quarterly, and annual inventory checks. Steps for the proper calibration of a differential pressure elbow flow meter: 1. Drainage: a. Close the valves on both sides of the three-valve assembly, open the middle valve, and then open the drainage valve to completely drain any impurities, ensuring that the pressure guide tubes are free of impurities and filled with the measuring medium. b. Open the exhaust valve at the back of the SMT3151 differential pressure and high-static-pressure transmitter to release air, so that the diaphragm chamber is also filled with the measuring medium. 2. Zero adjustment: With the valves on both sides of the three-valve assembly closed and the middle valve open, measure the static zero-current signal, and adjust it to 4.000 mA using the zero knob (Z). 3. Operation: Open the valves on both sides of the three-valve assembly and close the middle valve; the system is then ready for operation. Practical applications of the SMT3151 differential pressure and high-static-pressure transmitters have shown that their main advantages include: a simple and convenient installation and maintenance ； b The readings are intuitive, direct, and clear, allowing for an immediate determination of the oil inventory level ； c eliminates the need for density measurement and conversion. 4. Precautions for the use of SMT3151 differential pressure and high-static-pressure transmitters: (1) When designing and installing them, it is necessary to position the pressure-taking openings at the bottom of the oil tank as low as possible in order to eliminate errors caused by temperature changes; temperature compensation should be employed if necessary. (2) When the horizontal cross-section of the oil tank is not uniform (e.g., smaller at the top and larger at the bottom), compensation measures need to be considered. For secondary meters, the WP-H80 series level-volume controller is selected. (3) To achieve a certain level of accuracy, when a breather valve is installed on the top of the oil tank, the SMT3151 differential pressure transmitter must be used; the SMT3151 high-precision high-static-pressure transmitter cannot be employed in such cases. For open-top oil tanks or situations where high precision is not required, the SMT3151 high-precision high-static-pressure transmitter can be used directly to facilitate installation. (4) Where possible, use smart meters for secondary instruments, as they facilitate range adjustment and enable temperature compensation, among other functions. (5) During installation, a water collector must be installed in the negative pressure chamber of the SMT3151 differential pressure and high static pressure transmitter, and waste water should be drained regularly to prevent accumulated water from affecting accuracy. The volume (i.e., the number of tons), thereby preventing overflow. Based on this analysis, using the differential pressure method to measure liquid level (actually in terms of tons) is also a good option. Given that the SMT3151 differential pressure and high-static-pressure transmitters are currently widely used, and that this series offers an excellent cost-performance ratio, it is recommended to give them serious consideration. To ensure the relative accuracy and stability of the SMT3151 differential pressure and high-static-pressure transmitters when used in oil depots, 1) when measuring gas pressure with these transmitters, the pressure-taking ports should be located at the top of the process pipeline, and the transmitters themselves should also be installed in the upper part of the pipeline, so that any accumulated liquid can easily flow into the pipeline. 2. When measuring liquid pressure, the pressure tapping should be located on the side of the process pipeline to prevent sediment accumulation. SMT3151 differential pressure transmitter, SMT3151 high static pressure transmitter. 3. When measuring liquid pressure, the installation location of the SMT3151 high-precision pressure transmitter and the SMT3151 high-static-pressure transmitter should be such that it is protected from liquid impacts (water hammer effect), in order to prevent the sensors from being damaged due to excessive pressure. 4. Prevent residue from accumulating in the conduit. When making the connections, pass the cable through the waterproof connector (accessory) or flexible tube and tighten the sealing nut to prevent rainwater and other substances from seeping into the housing of the SMT3151 high-precision/high-hydrostatic pressure transmitter via the cable. 6. Prevent the SMT3151 high-precision high-static-pressure transmitter from coming into contact with corrosive or overheated media. SMT3151 differential pressure SMT3151 high-static-pressure transmitter. 7. The pressure guide tube should be installed in a location where temperature fluctuations are minimal. 8. When measuring steam or other high-temperature media, a condenser such as a buffer tube (coiled tube) must be used to prevent the operating temperature of the SMT3151 high-precision and high-static-pressure transmitter from exceeding its limits. This article was compiled by Huaheng Instrument and Transmitter Manufacturer