Purpose of Stop in a Pressure Measuring Instrument

Many industrial pressure sensing elements, especially diaphragms and bellows, are equipped with stops to limit the physical travel of the sensing element:

What important purpose is served by a stop in a pressure measuring instrument?

Stop in Pressure Measuring Instrument

A stop prevents the pressure element from being excessively strained by overpressure. Ultimately, it helps to prevent rupture of the element in the case of accidental overpressure.

When a pressure element flexes so far that it comes to rest against a stop, the stop begins to provide the opposition force to the force generated by the applied pressure, so the element does not have to strain further.

Ideally, the stop(s) in an instrument will be set up to limit the element’s travel enough so that its elastic limit is never exceeded. However, the presence of a stop does not guarantee that the instrument will remain within calibration specifications after exposure to an overpressure!

Stops are important even in force-balance transmitters where the pressure element (hypothetically) never moves.

Under certain overpressure conditions, the element will generate more force than the balance mechanism is able to counter, and so the pressure element will most definitely strain. A stop in a force-balance instrument helps ensure that even if the element strains, it will not strain too much.

Comments

What is a Torbar? – Averaging Pitot Tubes

The Torbar is employed for flow measurement of liquids, gases, or steam in circular, square, or rectangular section ducts for large flow rates. The Torbar is an insertion type multi-port self-averaging primary sensor for flow measurement. Torbar TORBAR is a set of Pitot tubes mounted on a bar across the pipeline with no moving parts. An averaging Pitot tube is a technology, while TORBAR is a manufacturing brand name. There are several brands available in the market with VERABAR, ANNUBAR, etc. Averaging Pitot Tube Principle Purpose Averaging Pitot tube can be employed when the average velocity of the flow profile, rather than the velocity in a specific point in the cross-section is desired. Averaging Pitot Tubes Principle It measures the differential pressure between the static pressure tap and the tap of full pressure of a stream. Thus such magnitude of differential pressure is directly proportional to the square of the flow rate. Working The TORBAR is designed in such a way that ...

Ferrules and Cross Ferruling

Ferrules are identification labels provided for every wire terminations in an instrument, equipment, or electrical/instrumentation control panels. These tube-shaped sleeves can be inserted easily on each individual wire in a multi-core cable. In earlier days fixed digits/letters are used as ferrules, but now Instrumentation engineers/technicians prints out desired ferrules by using a ferrule printing machine. Typical Ferrule The numbers/ letters on the ferrules will be given as per the approved electrical hook up or loop diagrams. This helps technicians to easily identify a particular loop/wiring from a series of terminal blocks and to troubleshoot the desired terminal connection. Separate numbers on the ferrules distinguish the positive and negative polarities of wires, thus ensure the polarity protection of the instrument. Cross Ferruling As a wire is connected on its both ends, it is quite useful to use a cross reference method for wire identification. Unlike normal ferru...

Thermowell Insertion and Immersion Length

The thermowell is the industrial housing for temperature elements like RTD or thermocouple or temperature gauges. Thermowell is directly exposed to process fluid/media. Inside the thermowell, element/gauge is installed. Thermowell transfers the heat to the temperature element. Depending upon the element type, the fluid temperature can be known. So Thermowell protects the temperature element against harsh conditions and process fluid. It enables removal of the temperature element for replacement, repair, or testing without affecting the process system. Generally, thermowells are provided with all-temperature Elements like RTD or Thermocouple or temperature gauge. A few exceptions would be bearing RTD, skin type thermocouple, air duct thermometer, etc where thermowell is not applicable / required. When the thermowell assembly is inserted into the pipe, it is subjected to vibration. This vibration is caused by vortices to be generated alternately on either side of the thermowell. The...

TILI Automation

Search This Blog