Skip to main content

Differential Pressure Switch Working Principle

 A Differential Pressure Switch, just like a regular pressure switch, is a simple electro-mechanical device that operates on the basic principles of levers and opposite forces. Mainly, they are used for sensing a difference between two points in a process. Three key elements are used in various combinations to manufacture different kinds of differential and standard pressure switches to suit unique industrial needs.

These elements are:

*A sensing element made either of bellows or diaphragm, metallic or elastomeric

*A hardened spring to determine the range set point

*A snap-acting micro switch available in a wide variety, SPDT, DPDT, etc.

Principle

The purpose of the Differential Pressure Switch is to sense a difference in pressure between two pressure sources in a control process. When the

pressure from two different sources is connected across a sensing diaphragm, the pressure difference creates a force which then acts upon the pre-tensioned spring. This action moves a balancing arm or mechanism to effect the minimal movement required to activate the micro switch.


High and low pressures are applied on either side of the specially contoured sensing diaphragm. This feature helps to eliminate errors due to a difference in area which is commonly a problem present in twin element Differential Pressure Switches.

Pressure ports for high-process pressure, as well as low-pressure are separated by an elastic diaphragm. The difference in pressure between the two ports causes axial movement, otherwise known as measuring travel, of the diaphragm against a measure range spring. The differential pressure, which is proportional to the measuring level, is transmitted through a connecting rod with little friction to the plungers of the micro switch.

The micro switch contains the electrical contacts of the switch, and electrical contacts will actuate based on the switch points and set points. Overpressure is protected by contoured metal bolsters for the elastic diaphragm.

Adjustments for Setpoints

The adjustment of the switch point or setpoint can be accomplished by setpoint screws accessible from the front of a Differential Pressure Switch. The graduated scales allow a relatively accurate adjustment of the switch points, and indicate the setpoint has been changed.

In short, Differential Pressure Switches work off the basis of a difference in pressure between two low and high points. The difference is converted to axial movement that is used to actuate the contacts of a micro switch depending on setpoints.

Working Principle
Process pressure is sensed by a diaphragm-piston combination. Hi-side system pressure acts on the piston to product force Fh. It is counteracted by the adjustable range spring force Fs and Lo-side system pressure acting on the backside of the piston to produce force Fl . The resultant force Fd acts on the piston and overcomes the force of the adjustable range spring [Fd = Fh – (Fl + Fs)] and moves a shaft that actuates (deactuates) an electrical switching element to generate a NO or NC contact.




Labels:

Comments

Post a Comment

Popular posts from this blog

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...
1 comment
Read more

PLC Program for Mixing Tank

 Create a ladder diagram for controlling a batch mixing process. Implement a PLC program for mixing tank or Mixing Process using PLC Ladder Logic. PLC Program for Mixing Tank Fig : Mixing tank A tank is used to mix two liquids. The required control circuit operates as follows: A. When the START button is pressed, solenoids A and B energize. This permits the two liquids to begin filling the tank. B. When the tank is filled, the float switch trips. This de-energizes solenoids A and B and starts the motor used to mix the liquids together. C. The motor is permitted to run for 1 minute. After 1 minute has elapsed, the motor turns off and solenoid C energizes to drain the tank. D. When the tank is empty, the float switch de- energizes solenoid C. E. A STOP button can be used to stop the process at any point. F. If the motor becomes overloaded, the action of the entire circuit will stop. G. Once the circuit has been energized, it will continue to operate until it is manually stopped. Solution...
2 comments
Read more

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 ...
7 comments
Read more