A differential pressure transmitter is the most common and helpful industrial measuring device. It is a highly accurate and powerful measuring instrument that helps keep the exact record of mass flow.
It helps measure the difference between two pressures by using two reference points. The low and high sides are two basic sides; the low side is the reference.
The instrument gives a positive or negative value depending on the flow direction, whether the flow rate on the low or high side is large.
How Does A Differential Pressure Transmitter Work?
A differential pressure gauge works to measure the difference between ton pressure points. After measuring the difference, the instrument covert the difference into the electrical signals, keeping a record and taking further precautionary steps.
A simplified overview of how the system maintains the record of flowing media is mentioned here for your assistance.
i) Pressure-sensing elements- Two pressure-sensing elements are on each side of the instrument. These sensing elements are in the form of a diaphragm or bourdon tubes.
ii) Fluid connection- The system has taps or ports that monitor the pressure difference. The transmitter is connected to this fluid system.
iii) Pressure difference- The pressure difference between two points may deform the pressure-sensing elements. Sensing elements on the higher side face more deflection, while those on the lower side may face less deflection.
iv) Deflection measurement- The deflection of sensing elements is converted into mechanical movements, which are then transferred to the sensing mechanism with the transmitter.
v) Transducer assembly- It changes the mechanical movements of the pressure-sensing elements into electrical signals. A strain gauge in the assembly changes the resistance in response to mechanical movements.
vi) Wheatstone bridge circuit- The bridge has a strain gauge that may imbalance the resistance. The purpose of this circuit is to balance the resistance changes, and imbalance resistance will result in the output voltage proportional to differential pressure.
vii) Signal conditioning- The voltage from the Wheatstone bridge is of small electrical signals amplified for any particular purpose. It does so to amplify the output signals.
viii) Output signal- The final result is the differential pressure in standardized electrical signals like 4-20mA or digital signals like HART or Modbus.
ix) Measurement and transmission- The output is then sent to the control system, data acquisition devices, or other instruments to record the pressure.
DP Transmitters Elements
The measuring instrument is constructed for industrial measuring purposes and covered with a strong body for housing the sensing elements.
It is also topped with a suitable compartment for housing the electrical or mechanical parts of the instrument, which are necessary to sense the pressure and then translate it into electrical signals.
If we categorize the differential pressure gauge into its working elements, the instruments have three basic elements.
1- Primary elements
The elements in this category cover the basic and foremost parts of the instruments. The basic primary elements are
i) Orifice plate
The plate is the important part of the primary element that introduces the pressure drop in the flow after introducing the restriction and comparatively has a small diameter.
The plate pressure transducer has two pressure connections connected to external monitoring devices. The connection connects the primary elements to the secondary ones.
ii) Venturi tube
The tube is the special arrangement in the primary elements that restrict the flow of media to create differential pressure. Its shape and pressure are more progressive compared to the orifice plate.
The venturi tube’s inlet, converging part, throat, and diverging part are some key components. Such types of flowmeters are usually used in the flowmeters to measure the flow.
iii) Flow nozzle
Flow nozzles are similar to the orifice plate, with more features and positive sides. The element is used in the transducers for better flow measurement. The flow meter comes in different forms, including,
- Flanged flow nozzle
- Flanged flow nozzles with integrated low pressure
- Weld-in flow nozzles
iv) Pitot tube
One bend pipe in the primary section of the instruments is known as a pitot tube. The tube has two openings.
One end of the pitot tube opens into the static area where the liquid flow rate is low, while the other directly connects with the flow.
v) Laminar flow element
As the name indicates, the portion makes the laminar flow of the media as it contains many long tubes.
The diameter of these tubes is larger than the main pipe and slows down the media flow. It also helps you get the linear relation between two terms, such as pressure drop and flow rate.
Moreover, the temperature is the main factor of this portion, as it affects the viscosity of the liquid and, ultimately, the final result.
Secondary elements
The major contribution of the secondary elements is to use the physical attributes to get the exact measurement of the flow.
Transducer helps make these conversions and helps you get the correct results. The overview of secondary elements is
i) Strain gauge pressure transducer
Such transducers are used to get the differential and narrow-span pressure measurements. With the presence of the strain gauge, a resistor creates resistance according to the strain you have applied to it.
It is connected to the diaphragm structure to change the pressure into strain. It is used in various instruments to measure differential, absolute, and gauge pressure.
ii) Resonant wire pressure transducer
As the name indicates, the resonant transducers have resonant wires according to the integrated oscillatory circuit.
A change in the pressure will change the tension in wires and, ultimately, the oscillation frequency.
The resonant wire transducers are stable under the stable physical condition, but the flow may not be linear. So, the element gets assistance from the microprocessor to maintain this non-linearity.
You will find such types of transducers in low-differential pressure applications.
iii) Capacitance pressure transducers
In this type of transducer, a moving diaphragm is used to determine the differential pressure to get the exact flow measurement.
A fill fluid known as liquid silicon connects this diaphragm to the primary element. This part of the secondary element also has a complex circuit that oscillates whenever there is a change in pressure.
If the system shows any change in the capacitance, the oscillation frequency changes, which is then translated into the DC signals.
Electronics
The last important element of the pressure transmitter is electronic, which amplifies and converts the raw signals into the PLC or any other suitable controller.
i) Voltage output
After getting the readings, you may get output in the form of voltage, depending on the configuration. The voltage range may vary between 0-10 or 0-5V.
ii) Current output
You may also get the output as a current; a 4-20mA current is necessary to feed into the PLC card.
iii) Digital output
You may receive two types of output: threshold output or digital communication data stream like RS232 and RS 485. These give digitally accurate and sampled readings of the flowing media.
Pressure Transmitter for Multiple Applications
The differential pressure sensor ICS is highly useful in large industrial sectors to keep the accurate flow rate of the media pressure. From the unlimited DPT applications, we have filtered a few important ones.
- Water and effluent treatments plants
- Used for various onshore, offshore, and subsea applications
- Largely used to monotone filters at large-scale plants
- Measure the pressure drop across the valve.
- Remote sensing of heating system for hot or steam water
- Oil and gas flow monitoring in industries
- It is also used at the commercial level
- Used to monitor sprinkle systems
- Pump control monitoring areas
Recpaing the Differential Pressure Transmitter
The DP transmitter helps you accurately record the pressure difference between two points among industrial instruments.
The HVAC differential pressure transmitter, in collaboration with numerous useful working elements, help you get the right output of the state or pressure inside the system.
Being highly effective and resilient instruments, the devices have massive demand in industrial sectors for better workflow.