A brief analysis of the advantages and disadvantages of pressure transmitters versus level transmitters

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This post was last edited by shrien on 2016-4-15 at 20:55. Transmitters can be divided into many types; more specifically, they are categorized as integrated temperature transmitters, pressure transmitters, and level transmitters. So, what are the differences between them? Pressure transmitters are also known as differential transmitters, and they consist mainly of modular circuits, pressure-sensing elements, display units, process connection fittings, and casings. It can convert pressure signals of the received liquids, gases, etc. into voltage signals of standard current, which are then supplied to secondary instruments such as indicating recorders, regulators, and alarms for measurement, indication, and process control. 　　The measurement principle of a pressure transmitter is as follows: the process pressure and the reference pressure act on opposite ends of an integrated silicon pressure-sensitive element; the differential pressure causes the silicon chip to deform (by a very small amount, only in the μm range), which enables the full-dynamic Wheatstone bridge fabricated on the silicon chip, using semiconductor technology, to generate a voltage signal in the mV range that is proportional to the pressure, driven by an external current source. Due to the excellent strength of silicon materials, both the linearity of the output signal and the distortion metrics are very high. During operation, the pressure transmitter converts the physical quantity being measured into a voltage signal in the mV range, which is then sent to a differential amplifier with a high gain that can cancel out temperature drift. The amplified signal is converted into a corresponding current signal through voltage-to-current conversion, followed by nonlinear correction, to ultimately produce a standard current-voltage signal that has a linear relationship with the input pressure. 　　Pressure transmitters can be divided into general pressure transmitters (0.001 MPa to 20 MPa) and micro-differential pressure transmitters (0 to 30 kPa), depending on their pressure measurement range. 　　Level transmitters are further divided into three types: float-type level transmitters, barrel-type level transmitters, and hydrostatic level transmitters. 　　Transmitters come in many different types. More specifically, they can be divided into integrated temperature transmitters, pressure transmitters, and level transmitters. So, what are the differences between them? A pressure transmitter, also known as a differential transmitter, is primarily composed of a pressure-sensing element, module circuits, a display gauge, a housing, and process connection fittings. It can convert pressure signals of gases, liquids, etc., received as input, into standard current and voltage signals for use by secondary instruments such as indicator alarms, recorders, and regulators for measurement, indication, and process control. 　　The measurement principle of a pressure transmitter is as follows: the process pressure and the reference pressure act on opposite ends of an integrated silicon pressure-sensitive element; the differential pressure causes the silicon chip to deform (by a very small amount, only in the μm range), which enables the full-dynamic Wheatstone bridge fabricated on the silicon chip, using semiconductor technology, to generate a voltage signal in the mV range that is proportional to the pressure, driven by an external current source. Due to the excellent strength of silicon materials, both the linearity of the output signal and the distortion metrics are very high. During operation, the pressure transmitter converts the physical quantity being measured into a voltage signal in the mV range, which is then sent to a differential amplifier with a high gain that can cancel out temperature drift. The amplified signal is converted into a corresponding current signal through voltage-to-current conversion, followed by nonlinear correction, to ultimately produce a standard current-voltage signal that has a linear relationship with the input pressure. 　　Pressure transmitters can be divided into general pressure transmitters (0.001 MPa to 20 MPa) and micro-differential pressure transmitters (0 to 30 kPa), depending on their pressure measurement range. 　　Level transmitters are further divided into three types: float-type level transmitters, barrel-type level transmitters, and hydrostatic level transmitters. 　　1. Float-type level transmitter The float-type level transmitter consists of a magnetic float, a measurement conduit, a signal unit, an electronic unit, a junction box, and mounting components. 　　Generally, the specific gravity of magnetic floating balls is less than 0.5, allowing them to float on the surface of the liquid and move up and down along the measurement conduit. The conduit is equipped with a measuring element that, under the influence of an external magnetic field, converts the liquid level signal being measured into a resistance signal proportional to the change in liquid level, and converts the electronic unit into a 4–20mA signal or other standard signals for output. This transmitter is a modular circuit that offers advantages such as acid resistance, moisture resistance, shock resistance, and corrosion resistance. It contains a constant current feedback circuit and internal protection circuits, which ensure that the maximum output current does not exceed 28mA; this allows for reliable protection of the power supply and prevents damage to secondary instruments. 　　2. Float-type level transmitter The float-type level transmitter replaces the magnetic float with a buoy; it is designed based on Archimedes’ principle of buoyancy. Float-type level transmitters use micro metal diaphragm strain sensing technology to measure the level, interface, or density of liquids. It can perform regular setting operations via on-site buttons while in operation. 　　3. Hydrostatic level transmitter This transmitter operates on the principle of measuring hydrostatic pressure of liquids. It generally uses a silicon pressure transducer to convert the measured pressure into an electrical signal, which is then amplified by an amplification circuit and compensated by a compensation circuit, before being output in the form of a current of 4–20mA or 0–10mA.