Application and Selection of Pressure Transmitters

In all types of measuring instruments, the transmitter is the most common. Transmitters are broadly categorized into two types: pressure transmitters and differential pressure transmitters. The pressure transducer 4-20ma can measure pressure, differential pressure, vacuum, level, flow, and density. The pressure transmitters are available in 2-wire and 4-wire systems, intelligent and non-intelligent. In addition, according to the application conditions, the pressure transmitter is mainly divided into the following types: low (micro) pressure transmitters, high-pressure transmitters, absolute/vacuum/differential pressure transducers, high temperature pressure transmitters, corrosion-resistant pressure transmitters, and easy-to-crystallize pressure transmitters.

The digital pressure transmitter selection is usually considered from the installation conditions, environmental conditions, instrument performance, economy, and application media. Common digital pressure transmitters are ordinary pressure transmitters, differential pressure transducers, single flange level transmitters, double flange level transmitters, and so on.

Nominally, digital pressure transmitters measure pressure, while differential pressure transmitters measure the difference between two pressures. But, they indirectly measure more parameters than just pressure. For example, in addition to measuring pressure, a digital pressure transmitter can also measure the liquid level inside a device. When measuring the liquid level of an atmospheric pressure vessel, one pressure transducer 4-20ma can achieve the measurement. When measuring the liquid level of a pressurized container, two pressure sensor transmitters are required. Among them, one for the lower limit and one for the upper limit. Then, subtract their output signals to measure the liquid level. The pressure sensor transmitter can also measure the density of the medium in the case of constant liquid level and pressure values in the vessel.

In addition to measuring the differential pressure between two measured pressures, the differential pressure transducer can also be used with various throttling elements to measure flow values.

In terms of fabrication structure, the pressure transducer 4-20ma can be divided into two types: ordinary type and isolated type pressure transmitter. The ordinary type pressure transmitter has a measuring diaphragm box, which directly feels the pressure and differential pressure of the measured medium; the measuring diaphragm box of the isolation type pressure transmitter receives the pressure of a kind of stabilizing liquid (generally silicone oil), which is in a sealed state between the two diaphragms. The isolated type pressure transmitter has a remote type and a body type.

The pressure transducer 4-20ma selection is mainly based on the following principles: the nature of the measured medium indicators prevail, to save money, easy installation, and maintenance as a reference. When selecting the type, we should consider the corrosion of the measured medium on the sensor metal, and we must choose the suitable material for the sensor. The sensor materials include ordinary stainless steel, 304 stainless steel, 316L stainless steel, and tantalum. We also need to take into account the temperature of the measured medium. If the temperature is high, use the high-temperature type, otherwise, the silicone oil will produce vaporization expansion, making the measurement results inaccurate. Secondly, when selecting the pressure transmitters, we should also consider the pressure level of the equipment work. The pressure level of the transmitter must be compatible with the application.

From an economic point of view, the selection of digital pressure transmitter, as long as the medium is not easy to crystallize can be used as ordinary digital pressure transmitters, and for low-pressure crystallization of the medium can also be added to the blowing medium to indirectly measure (as long as the process allows the use of blowing medium), the application of ordinary digital pressure transmitter is to require maintenance personnel to carry out more regular inspections, including a variety of pressure-guided tube leakage, blowing the medium is normal, whether good insulation etc. As long as the maintenance is good, a large number of ordinary pressure transmitters will save a lot of one-time investment.

At present, the smart pressure transmitter has been quite popular. Auto's smart pressure transmitters are highly accurate, have a large adjustable range, are easy to adjust, stable, and very reliable.