Monthly Archives: May 2016

Differential Pressure Transducer

Pressure Transducers – Saving Lives, Property and Maximizing Production Capabilities

A pressure transducer can directly measure the force of gas or liquid, and convert the value into an electrical signal. Pressure transducers typically include a sensing diaphragm capable of responding to changes in pressure. Pressure pushes on this diaphragm, changing its position, and this changes the inductance of sensing coils mounted opposite the sensing diaphragm. The coils are excited with an AC waveform and the resulting change in electrical impedance represents the applied pressure. The electrical output of the coils is converted to a DC signal.

Pressure Transducers – Classifications

Pressure transducers come in a variety of shapes, sizes, and output signal types. In addition to a DC voltage output, current signals are often used for electrically noisy environments commonly present in industrial applications. A 4 to 20 mA signal has been adopted as the industry standard and the current signals can be sent accurately beyond 1,000 feet. All pressure transducers are generally characterized by their pressure measurement range. They are also classified by accuracy, errors due to temperature change, and the amount of static pressure the sensor can tolerate. Temperature always affects transducer accuracy and most transducers have a scheme to correct for ambient temperature changes Resolution is another characteristic used to evaluate a pressure transducer, and this is defined as the smallest amount of pressure change that can be detected – typically a function of the signal-to-noise ratio of the output.

Electromagnetic interference (EMI), can also affect transducers. Some units are protected against EMI effects, but only up to certain intensities. Materials used to make the sensors vary, and include plastic, silicon, stainless steel, or epoxies. Epoxies can be adversely affected by certain fluids under pressure.

Some pressure sensors are mounted to a circuit board with contacts to secure a solid connection. Others are designed for industrial environments and sturdily constructed with weatherproof enclosures. If the device is for general use, it is likely to have a standard design that allows it to easily connect to commonly used receiving devices such as computers, programmable controllers and panel meters. The costlier transducers are known for their high-accuracy readings and low rates of error as a percentage of full scale range. At Validyne, we offer many different configurations to meet your exact requirements.

Types of Transducers

At Validyne, we serve several major markets and carry a variety of transducers, which include differential pressure sensors, gage pressure transducers, USB pressure transducers, electronic pressure manometers, low pressure transducers, OEM pressure sensors, and more.

Transducers perform a critical job in every industry, especially in automation and control. Transducers used in aircraft or healthcare applications have lives depending on reliable and accurate performance.

For Simplicity and Accuracy, Nothing Beats a Pressure Manometer

Industries have many requirements for measuring pressure. Applications include measuring fluid levels, tank pressures, flow rates or hydraulic system pressures. For the measurement of low pressures, one such device is called a pressure manometer.

Manometers were first used shaped as a U-tube – is simply a tube filled with liquid. The unit functions on the principles of gravity and the density of the liquid being measured. A ruler or scale is used to measure the height of the fluid in the U-tube and this directly reads the pressure present. Pressure ranges for manometers are as small as a few inches of water column to several feet.

Measuring Air Flow
A pressure manometer is often used to measure the air-flow speed. Moving air creates a force that is proportional to velocity. This force, typically just a few inches of water column, is applied to the manometer for measurement and then converted to flow by a simple calculation. The measurement of flow in air in ducts and ventilation systems is one such use of the manometer.

Medical Applications
Another use of manometers is the measurement blood pressure using an air cuff. Low pressure manometers may also be used to measure the flow and pressure in a patient’s airways. Manometers have also been used in industrial settings, wind tunnels, and the measurement of atmospheric pressure for weather forecasting.

Digital Manometers
There are many manometer designs to choose from. Most manometers available now are digital models. This is because fluid manometers using mercury are considered a toxic hazard. At Validyne, our manometers work by using a pressure transducer instead of a column of fluid to make the pressure measurement. Digital manometers can be utilized with any equipment that relies on gas or liquid to operate.

Manometers can also isolate system pressure problems from barbecue grills to propane and natural gas. The HVAC industry, on occasion, will use these units to troubleshoot air conditioning and heating systems. Manometers can also be used to troubleshoot a wide variety of pneumatic or low-pressure gas systems.

Advantages of a Pressure Manometer
There are several advantages of using electronic manometers. An electronic manometer is portable and more compact than the old fluid-filled types. The electronic manometer is more accurate and provides a greater resolution than older versions, and a digital display is easier to read.

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

The Basics of the Aerospace Pressure Transducer for Flight Testing

Many of us have traveled via plane at some point in our lives. Even if you’ve never set foot on a plane, you’re likely to have seen them throughout your life. No matter if you have flown before or not, most of us can agreed we never really spent a whole lot of time thinking about how they work. Keeping a plane, or any aircraft for that matter, in the air is a complicated process that relies on specific equipment. A pressure transducer is one piece of equipment that is involved in the flight process of all aircrafts.
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