Tag Archives: differential pressure transducer

Differential Pressure Transducer

What to Look for in Durable Differential Pressure Transducers?

At Validyne Engineering, we have almost half a century in the industry, providing a range of different low cost, highly accurate pressure sensors for many different industries and applications. Over time, we have provided these sensors to various industries and companies. We have also listened to the needs of our customers to develop the sensors, transducers and transducers to get the job done.

One of the most important aspects of our devices is quality. We produce a durable, rugged line of differential pressure transducers. We believe we have a top selection of these transducers for all industries and applications.

The Validyne Difference

All of our differential pressure transducers are designed to meet performance specifications in highly demanding environments. Most of the transducers we sell can be used for both liquids and gases. They have been extensively used in the field with test vehicles and aircraft as well as in all types of environmental conditions.

Our in-house team of designers and engineers, all with extensive experience in sensor component development and design, has the ability to incorporate the needs of our customers into specialized solutions for their applications. We are also able to take this knowledge and design transducers for general use that are superior to other designs on the market today.

Up to the Test

One of the biggest complaints we hear from people looking for transducers is their inability to survive difficult working conditions. Each of our components has been thoroughly tested to provide our end-users with the quality part to stand up to real-world use. We also provide support and assistance in helping you to choose the right component for any application.

Our transducers are able to handle changes in the environmental and ambient temperatures with minimal impact on the accuracy of the pressure readings. They are designed to provide precise readings with fast response, giving test engineers the data they require. Fully compatible with data management systems, they are easy to integrate into field or laboratory testing situations or where and as they are needed.

Easy to mount with pre-drilled holes, they have a small, compact size and low weight make these differential pressure transducers the right component for the job. They are able to stand up to spray and moisture and also capable of wet-wet operations. Our transducers are available in differential or absolute pressure, as well as the option for a CE approved model if so required.

P55 Pressure Transducer Handbook Now Available

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The P55 Pressure Transducer Handbook is a complete one-stop source of information on the Validyne P55 pressure transducer in a single pdf file.

Here is the Table of Contents:

P55 Data Sheet

General Operating Instructions

Sample Calibration Data Sheet

Outline Drawing

Wiring Diagrams

Calibration Procedure

Protecting Against Hot Fluids – Temperature Isolation

Bench Testing the P55

Definition of P55 Specifications

Returning a P55 for Repair

Download your copy here.

Application Note: Basics of Air Velocity, Pressure and Flow

Air velocity can be measured by sensing the pressure produced by the movement of the air. This application note will describe the basic relationships between air velocity and the pressure generated by air flow.

Anyone who has put their hand out the window of a moving car has experienced the force applied by moving air. This force can be sensed as a pressure by connecting a tube from the positive port of a differential pressure transducer like the P55 differential pressure transducer and pointing the open end of the tube directly into the oncoming air stream. The figure below shows how this might look.

Differential Pressure Transducer Air Velocity

The tube that is placed into the air stream is called a pitot tube after Henri Pitot, the French engineer of the early 18th century who invented it. As the velocity of the air increases the pressure also increases inside the pitot tube with respect to the ambient atmosphere. A differential pressure sensor like a DP15 Range Changeable Pressure Sensor can be plumbed to measure this when the pitot tube is connected on the + port and the – port is open to atmosphere. Note that the pitot must be pointed directly into the flow – if the tube is mounted at some angle to the direction of flow, the transducer will not sense the full pressure developed by the air velocity.

The pressure developed by the air velocity is called the velocity head, and it is affected by the density of the air. The density of the air, in turn, is a function of the local atmospheric pressure and the temperature. The equations that relate all these factors are:

airflow-3 air velocity

Note that to determine the air velocity the density must first be known. This is the second equation and relates ambient atmospheric pressure and temperature to density. The temperature in degrees Rankine is an absolute reference and is T in degrees F + 460. Assuming average conditions of 70 F and a barometer of 29.92 In Hg, the density of air is 0.075 Lbs/Cu Ft.

If, for example, we measure a differential pressure from the pitot tube of 2.00 In H2O, then the air velocity calculates to 5671 ft/min or 94.5 ft/sec.

Air velocity is a function of air density and differential pressure, but determining air flow requires that the geometry of the piping be taken into account. The pitot tube can be used as before, but  the negative port of the pressure transducer is now connected to the pipe or duct so that the internal pressure is taken into account by the measurement of the velocity head.

Differential Pressure Transducer air velocity

Note that it is still critical that the pitot tube be installed so that it is pointed directly into the oncoming flow stream.

Ideally, determining the flow in terms of volume should simply a matter of multiplying the cross sectional area of the tube or duct by the air velocity. If the dimensions of the ducting are known, then the cross-sectional area can be easily determined and the volumetric flow calculated.

There is a problem with this, however – the velocity of the air is not uniform at all points along the cross-sectional area of the tube. This is because friction between the moving air and the inside surface of the pipe or duct slows the velocity down. The air velocity in a pipe, for example, is highest near the center but slows towards the inside walls. To make things even more complicated, the shape of the velocity profile is also affected by the type of flow – turbulent or laminar – and the proximity of other fittings and protuberances inside the piping.

airflow-4 air velocity

Averaging pitot tubes have been developed that sense the velocity head at several points along the cross-section of the air pipe or duct and deliver a differential pressure that more accurately reflects the average velocity profile.

airflow-5 air velocity

The extent to which the averaging pitot tube differential pressures deviate from the actual velocity profile pressures is expressed by a correction factor supplied by the manufacturer. This factor may depend on duct geometry and the flow regime present – sizing a pitot tube correctly has become an art. But the pitot tube factor must also be included along with the other variables in the final flow equation.

The Validyne P55 Pressure Transducer can be used to measure flow. Click here now to contact us for more information. 

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