Differential pressure gauge | DP flow

How a differential pressure gauge works 

A differential pressure gauge (sometimes called a differential pressure transmitter) measures the difference between two pressure points. It is used, for example, to monitor flows in pipes, detect filter clogging or measure levels in tanks. Below is a basic explanation of how such a gauge works: 

1. Two separate pressure ports:
   The differential pressure gauge usually has two connections - one for the high pressure side (High, H) and one for the low pressure side (Low, L). The pressure from these connections is fed into a sensor or measuring diaphragm inside the instrument. 
2. Measuring membrane or sensor:
   Inside the gauge there is often a diaphragm or other elastic sensor. The pressure difference between the H and L sides creates a force that bends or moves the diaphragm proportionally to the size of the difference. The greater the pressure difference, the more displacement. 
3. Conversion to output signal:
   The mechanical movement (e.g. displacement of the diaphragm) is converted into a measurable signal. Depending on the measurement system, this can be: 
   • Mechanical: A dial indicator moves on a scale that shows the pressure difference directly in e.g. bar or Pascal. 
   • Electronically: The movement in the sensor is converted via, for example, piezoresistive or capacitive sensors and produces an electrical signal (4-20 mA, 0-10 V, digital BUS, etc.) which can then be read or controlled in a control system.
4. Calculation of the difference:
   The internal construction of the instrument is made to measure (H - L). For example, if H is 5 bar and L is 3 bar, the gauge will show 2 bar of differential pressure. 

Applications: 

• Flow measurement: Often used with throttling flanges or venturi tubes. By measuring the pressure drop across a restriction in a pipeline, the flow rate can be calculated. 

• Filter monitoring: If the differential pressure across a filter rises, it means that the filter is likely to start settling again. 

• Level measurement: In tanks with liquid, differential pressure can be used to determine the liquid level (measuring the pressure difference between the liquid column at the bottom and the pressure above the liquid).