Frequently
Asked
Questions
Diaphragm seals (also known as chemical seals or remote seals) are used for pressure measurements when the process medium should not come into contact with the pressurized parts of the measuring instrument.
The Pressure diaphragm has two main tasks: to separate the measuring instrument from the process medium; to convey the pressure to the measuring instrument.
The process side of the diaphragm is separated by a flexible diaphragm. The internal space between the diaphragm and the pressure measuring instrument is completely filled with the system fill fluid.
The pressure is transmitted from the measured medium to the filling liquid through the elastic diaphragm, then from the filling liquid to the measuring element, and finally to the pressure measuring instrument, such as a pressure gauge or a pressure gauge transmitter.
Typically, diaphragm seals are mounted on existing fittings or flanges. Fittings consist of T-pieces that are integrated into pipes or welded to pipes, process reactors or tanks. The advantage of this diaphragm seal is: The “contact surface” between the pressure medium and the diaphragm becomes relatively large. This ensures accurate pressure measurement, especially for extremely low pressure conditions (<60 kPa).
The diaphragm seal can be easily removed, e.g. for cleaning or calibration purposes, which is another advantage.
In addition to measuring pressure, pressure transmitters can also be used for many purposes. For example, using differential pressure transmitters to measure flow and using liquid gravity to measure liquid levels. Diaphragm level transmitter is a commonly used pressure level transmitter.
Working principle of diaphragm level transmitter
The working principle of the static pressure level transmitter is: the static pressure of a certain point in the liquid is proportional to the distance from the point to the liquid surface, that is: P=ρgh. Among them: P-pressure (pressure) of the measured point, ρ-medium density, g-gravitational acceleration, h-height from the measured point to the liquid surface. For the determined measured medium ρ, g is a constant, so the change of the position from the measured point to the liquid surface is only related to the measured P pressure (pressure).
When measuring liquid levels in open containers, a pressure transmitter is all that is needed.
When measuring the liquid level of a closed pressure vessel, two pressure or one differential pressure transmitter can be considered. That is, one set for the lower limit of measurement and one set for the upper limit of measurement. Their output signals can be subtracted to measure the liquid level. At this time, a differential pressure transmitter is generally used. It can also be used to measure the density of the medium when the liquid level and pressure in the container remain unchanged.
For airtight containers, since the interior is isolated from the atmosphere. When a process fluid fills or empties a tank, the pressure inside the tank may change from positive to vacuum. This change in tank pressure directly affects the measured liquid level unless compensated for. Connecting the low side tubing from the differential pressure transmitter to the top of the tank will do this. Therefore, when measuring the liquid level of a closed tank, a differential pressure transmitter must be used.
There are many types of pressure transmitters. Here we introduce 4 common types:
- Gauge pressure transmitter:
The gauge pressure transmitter is a pressure transmitter with the local atmospheric pressure as the reference zero point. - Pressure transmitter:
The pressure transmitter is a pressure transmitter with vacuum as the reference zero point. During use, the reference zero point of the sensor can be automatically adjusted without correction as the location and region change. The appearance is the same as the gauge pressure transmitter. - Differential pressure transmitter:
The differential pressure transmitter is a pressure transmitter that measures the pressure difference between two pressure chambers. The differential pressure transmitter has two pressure chambers of “+” and “-. Undertake two pressures as comparison values respectively, and usually use the end with higher pressure as the “+” pressure chamber. - Input/insert type liquid level transmitter:
Liquid level transmitters are divided into two types: input type and plug-in type. The two forms are the same, and both convert the pressure to the liquid depth. When the water depth is 1m, the pressure on the transmitter is 10KPa,
