Category Archives: Pressure-Sensors

Pressure Sensors and External Carrier Demodulators

The most popular Validyne pressure transducers are the P55/P61/P365 series.  These all include a pressure sensor, carrier demodulator electronics package, a high level output signal, temperature and linearity correction as well as a compact form factor.  There are applications, however, where a better solution might be to separate the pressure sensor from the electronics, with the two connected by a cable.  This article describes when this approach makes the most sense.

Validyne offers the sensors and electronics package from the P55/P61 available as stand-alone components.  The DP15 series of pressure sensors is identical to that used in the P55 and P61, while the DP360 and DP363 are high pressure variants the same as used in the P365 and P368.  The CD16 standard analog output electronics or the CD17 USB-based electronics can be used with any of these sensors, and standard cables are available in a variety of different lengths to connect the two.

Pressure Sensors

When should a sensor be separated from the electronics?  The biggest reason to do this is to allow convenient re-ranging of the pressure sensor.  The full scale pressure range of Validyne sensors can be changed by replacing the sensing diaphragm.  There are 23 different full scale ranges available for the DP15, for example, and these run from a few inches of water to 3200 psi. Changing the diaphragm is straightforward; the connector and four body bolts must be removed to gain access to the sensing diaphragm, and the DP15 sensor makes this easy, requiring just a torque wrench and a vise.  With a little practice, the diaphragm in a DP15 can be replaced and re-calibrated with the CD16 or CD17 electronics in about 20 minutes.  The DP360 and DP363 high pressure sensors are similar in construction and also lend themselves to straightforward diaphragm replacement. Frequent re-ranging of the full scale of a Validyne transducer is common in laboratory situations where pressure measurements vary widely from day to day.  Test labs and university labs are typical places where a separate sensor and electronics package are used to best advantage.

Another reason for separating the pressure sensor from the electronics is to conserve space or limit the weight at the measurement point.  In tight locations, such as aircraft compartments or in submersible vehicles, the pressure connection may be in a relatively inaccessible space and the smaller footprint of the DP15 sensor, might fit better than the full P55.  If mass or weight is important, the sensor will be lighter than the full transducer and this will relieve any stress on the piping connections in areas where shock and vibration are a consideration.

It is important to realize that separating the sensor from the electronics will compromise the temperature correction as the temperature sensor is located on the electronics package and not at the pressure sensor.  A pressure sensor such as a DP15 used with a remote electronics such as the CD16 will be most effective in applications having a stable temperature environment.

 

Signs of a Faulty or Failing Differential Pressure Sensor

There are many different types of pressure sensors that are used to measure a number of applications and operations. From use in automobiles, measuring flow rates in pipelines, density measurements, and even for measuring the levels of fluids, a differential pressure sensor can be the best option.

The Basics of Operation

The differential pressure sensor is a method of measurement based on two different reference pressures. The sensor is designed to allow access to either side of a diaphragm by the liquids or gases. This creates a pressure against the central diaphragm on both sides.

A gauge is used to read or measure changes in the pressure on either side of the central diaphragm. This can include an increase in pressure on one side, or a drop in pressure on the other. The sensor measures the deformation of the diaphragm, and converts this change into an electric signal.. It can also transmit that information directly through USB, wireless, or other digital methods to computer systems that monitor, record, and control the flow or another variable.

Signs of Failure

The most common issue with a differential pressure sensor is damage to the diaphragm that causes it to be deformed, or to lose the ability to flex and respond to changes in pressure.

This is most often caused by extreme bursts of pressure that are atypical for the system. It can also be caused by installing the wrong size or type of sensor, given the operating conditions.

Another issue that can occur is damage to the port area of the sensor. This may occur if there is some type of debris or contamination within the system that lodges in the port or the tube, restricting the correct flow of the fluid into the sensor.

If your Validyne pressure sensor or pressure transducer is not performing as it should, contact sales@validyne.com so we can help you get it fixed!

Corrosion Resistance of Validyne Pressure Transducers

Pressure transducers are exposed to a wide variety of fluids and gases when used to measure pressure.  Corrosion of the pressure transducer sensor body will shorten service life and lead to costly downtime if material selection is not carefully considered.  This article will cover the basics of material selection for Validyne pressure transducers so that the best possible performance and adequate corrosion protection can be ensured prior to purchase.

Validyne offers three types of sensor body materials that will provide appropriate protection for most pressure measurement applications: 410 SS, 316 SS and Inconel.  316 SS and Inconel pressure transducers are supplied with a teflon-coated 410 SS sensing diaphragm needed for the Validyne inductive sensing technology to operate correctly.

410 SS

410 is the standard material for Validyne transducers and does best when used with air, inert gases, or hydrocarbon-based fluids.  Oxidizing environments – or fluids containing chlorides – will cause 410 SS to corrode and pit, sometimes rapidly.  Water-based fluids, fluids containing salts, or corrosive chemicals should not be used with 410 SS.

Validyne offers the P365 High Pressure Transducer and the P368 Digital High Pressure Transducer with the 410 SS option.

316 SS

316 SS is the standard steel for instrumentation and has a high degree of resistance to water-based fluids and mildly corrosive chemicals.  316 SS also does well in fluids with low concentrations of chlorides, but is attacked by nonoxidizing acids such as sulfuric and hydrochloric acid in most concentrations.  316 SS has good resistance to alkaline solutions, organic acids, and other organic compounds.

Validyne offers a wide range of pressure sensors and pressure transducers with 316 SS.  The DP15 Variable Reluctance Pressure Sensor Capable of Range Changes, P55 Pressure Transducer and P61 USB Pressure Transducer are some of the pressure transducers that can be ordered in 316 SS option.

Inconel

inconel pressure transducers

Inconel is a superior material, ideal for corrosive applications, and is best reserved for systems containing high concentrations of chlorides such as salt water or brine.

Validyne offers a full range of pressure sensors and transducers in inconel. From low-static pressure transducers to high-static pressure transducers, we offer the DP15 Variable Reluctance Pressure Sensor Capable of Range Changes, P55 Pressure TransducerP61 USB Pressure TransducerP365 High Pressure Transducer and the P368 Digital High Pressure Transducer.

Fluids to Avoid

Fluids containing hydrogen or hydrogen sulfide should not be allowed to come in contact with Validyne transducers. Almost all metals lose ductility when they absorb hydrogen, especially at temperatures below 100 °C. Hydrogen molecules can enter the sensor body metals at the grain edges and this will cause embrittlement of the metal that can lead to pressure boundary failure.  Additionally, hydrogen sulfide is poisonous and hydrogen gas is extremely explosive.

Corrosion of Validyne transducers is not covered by the warranty. The proper choice of sensor body material will enhance pressure transducer performance and increase the life of the pressure transducers.

Click here to contact us today to find out the different solutions we can provide for your pressure measurement application. 

Differential Pressure Sensor

A Differential Pressure Sensor Offers Value in Many Industries

Pressure gages have been around ever since the steam age and differential pressure sensors are hard at work monitoring fluid pressure, flow, level and vacuum.

How Does a Differential Pressure Sensor Work?

Validyne differential pressure sensors operate on the variable reluctance principle. Two coils are mounted normal to the plane of a sensing diaphragm. As the diaphragm is deflected by pressure, the impedance changes in the coils are detected and electronically converted to a voltage or current signal proportional to the applied pressure. The signal is sent directly to a control panel that displays the results or a computer interface for analysis.

Pressure Sensor Types

Gage, absolute and differential pressure sensors are the most commonly used pressure transducer types. A gage pressure sensor measures pressure with respect to ambient atmospheric pressure. Absolute pressure sensors are referenced to a complete vacuum. Differential pressure sensors measure the pressure difference between the two pressure ports.

Our Products

At Validyne, we offer an entire line of pressure sensors for every industry purpose and application. Industries served include medical, oilfield, steel and glass, chemical, aviation, automotive, research and many more. Pressure transducers are used in automation of industrial processes, scientific research, the protection of equipment, and in medical applications can ultimately save lives.

Measuring Vacuum Pressures

A subject that tends to cause confusion when specifying pressure transducers is the  measurement of a vacuum and how it relates to absolute pressure.

Here are some definitions:

Absolute Pressure – A pressure referenced to zero absolute pressure.

Gauge Pressure – A pressure referenced to the local atmospheric pressure

Differential Pressure – The difference in pressure between two points.

Vacuum – A pressure less than the local atmospheric pressure.

From the above definitions we can see that an absolute pressure is measured starting from absolute zero – the complete absence of pressure. The complete absence of pressure exists in space, but on the surface of the earth the atmosphere exerts a pressure of about 14.7 psia at sea level. A barometer is a device that uses a column of mercury to measure the atmospheric pressure and this ranges from about 27 In Hg to 33 In Hg, depending on the weather. In addition to varying with the weather, the local atmospheric pressure also depends on elevation. The atmospheric pressure is about half that at sea level when you are at an altitude of 17,000 feet.

A vacuum is any pressure less than the local atmospheric pressure. It is defined as the difference between the local atmospheric pressure and the point of measurement. A vacuum is correctly measured with a differential pressure transducer that has one port open to atmosphere. If, for example, the negative port is connected to a vacuum and the + port open to atmosphere, the transducer signal will increase as the vacuum increases. It will always indicate the correct vacuum, even when the local atmospheric pressure changes with the weather.

An absolute pressure transducer cannot measure vacuum directly. If connected to a vacuum the signal from an absolute pressure transducer will decrease as the vacuum increases, but you can only know the actual vacuum if you know the local atmospheric pressure because vacuum is always referred to the atmosphere. Another way of thinking of a vacuum is that it is a negative gauge pressure.

The local elevation will affect a vacuum measurement because the atmospheric pressure is affected: no matter how powerful your vacuum pump, you cannot pull a vacuum of 14 psi at an elevation of 6000 feet – because the atmosphere there is only about 12.5 psia and the difference between the atmosphere and a vacuum cannot exceed that pressure.

In summary: a vacuum is best measured with a differential pressure transducer having one port open to atmosphere.

Check out Validyne’s absolute, vacuum, gauge and differential pressure transducers.

measuring vacuum