Tag Archives: Pressure Transducer

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.

 

pressure sensor

Pressure Sensor Accuracy

When using a pressure sensor to measure pressure, one of the first questions that comes up is accuracy: How closely does the value reported by the pressure sensor come to the actual pressure?  We use the term accuracy, but what we really want to know is the error of the pressure measurement.  This article will describe standard specifications and methods for calculating sensor accuracy.

The definition of sensor accuracy actually defines error, and the two terms are used more or less interchangeably:  The accuracy of the sensor is the simply the difference between the pressure reported by the sensor and the actual pressure, expressed as a percent of the sensor full scale.  For example, if a pressure sensor with a full scale range of 100 psi reports a pressure of 76 psi – and the actual pressure is 75 psi, then the error is 1 psi, and when we divide this by the full scale and express it as a percentage, we say that accuracy (or error) of the sensor is 1%.  Most industrial sensors are better than that, with specified accuracies of +/-0.25% or +/-0.1% of full scale (FS).  So the error of a 100 psi FS sensor with an accuracy of +/-0.1% FS will not exceed +0.1 psi or -0.1 psi – at any point in the measurement range of the sensor.

Sensor accuracy is comprised of two error modes: Non-linearity and Hysteresis.  Ideally, pressure sensors are perfectly linear – the output signal or reading is directly proportional to the applied pressure.  Because sensors are mechanical devices, however, they are not perfectly linear, and this error is called non-linearity.  Non-linearity is determined by the five-point calibration method.  A pressure standard (a device know to be at least five times more accurate that the pressure sensor) is used to apply pressures at 0%, 50%, 100%, 50% and 0% of the sensor full scale.  A best-fit straight line is fitted to these points, and the maximum deviation of any of the five points from the value predicted by the best-fit line, is defined as the non-linearity error.

Hysteresis is simply the difference in the value of the readings at the same pressure along these five calibration points, up-scale and down-scale.  Hysteresis can be measured from the readings at the 50% points and at 0% FS pressure.  The greatest difference in any of these is defined as the hysteresis.

The accuracy of the sensor is defined to be the sum of the non-linearity error and the hysteresis error.

Note that the sensor accuracy calculation is pretty much the worst case error that can be determined from the calibration data, and it may not occur at every point along the pressure sensor FS range.  But this is considered to be a conservative method for calculating the error present at any pressure over the range of the sensor.

For differential pressure sensors – those having a plus and minus full scale range, the same techniques are used to calculate accuracy with the addition of -50%, -100%, -50% and 0% calibration points required (9 all together).

Spreadsheets that automatically calculate non-linearity, hysteresis and accuracy are available from Validyne for gage, absolute and differential pressure sensors.  Factory calibration sheets showing these errors are shipped with most sensor models.

5 Things to Consider when Working with a Pressure Transducer

Pressure is crucial in fluid-power circuits. Using a pressure transducer allows you to control your system. Connecting the transducer a power source, while plumbed to a pressure source, generates an electrical output signal that matches the pressure. However, there are many considerations when you use this equipment. Here are some of them:

The Pressure Range

Since pressure transducers are designed to provide electrical output to match any given pressure range, make sure you pick a pressure transducer with a full scale range that is closest expected pressure. Also, check and confirm if the electrical output signal is matched to the needs for your existing system. Compatibility issues can compromise results or damage the pressure transducer.

Quality

Using trustworthy suppliers, such as Validyne, to source a premium-grade pressure transducer should be a priority. In doing so you won’t have to contend with units that exhibit low-quality performance. Opting for the right suppliers will keep those superior-quality transducers coming whenever you need them.

Installation

Be careful not to damage the electrical connector during the installation process. Denting a pin or connector shell could damage your unit. To prevent this from happening precisely follow the installation guidelines. If you have any doubts, ask for an installation professional for help. Be sure to connect the pressure transducer pressure ports with high quality NPT fittings and use Teflon tape on the threads.

System

Accuracy and reliability are important. Check to make sure the cabling, readout devices, signal conditioning, and amplification units are all in good working condition. Don’t forget about the power wiring to the transducer, as that is a common spot for trouble.

Maintenance

You will need to ensure the transducer receives proper maintenance and care. That’s the best way to ensure optimum performance. Regularly check the pressure transducer pressure connections for leaks, and tighten as needed. Also, keep all electrical connections between the system and components free of water and spray.

Keeping your transducer functioning at top form is crucial, so keep these practical tips in mind. If you need to know more about transducers, seek contact us today!

The Operation of, and Benefits Provided by, Our Variable Reluctance Pressure Transducer

All pressure transducers sense pressure from the outside mechanically and produce an electrical signal in response to these changes.

When it comes to the variable reluctance pressure transducer, a sensing diaphragm changes position with pressure, inductively changing the impedance of the two sensing coils. This change produces an electrical signal.

As the potential user of pressure transducers, you need to know what type of unit is best suited for your particular application. At Validyne Engineering, we can point you in the right direction to find the pressure transducer that matches your particular needs.

Let’s look at the Variable Reluctance Pressure Transducer

The VR pressure transducers we offer at Validyne Engineering consist of a flat diaphragm (magnetically permeable) supported between two coils. A magnetic field is produced between the coils and the diaphragm when an AC excitation is applied. The opposition to the lines of flux (called the reluctance) is determined by the air gap present between the two coils and the diaphragm. The coils are wired electrically as an inductive half-bridge.

In this arrangement, an AC signal is produced in direct proportion to the deflection of the diaphragm. This is how it works: with the diaphragm in a relaxed, or ‘zero’ state, position, the magnetic field between coil 1 and the diaphragm is balanced with the magnetic field between coil 2 and the diaphragm. So there is a gap produced depending on the position of the diaphragm and each coil. This produces an AC output voltage.

Particular benefits provided by the variable reluctance pressure transducer include:

  • Measurement of very low pressures
  • Low power consumption
  • Wet/Wet differential measurements
  • Suited for high levels of vibration
  • Fast Dynamic Response

The variable reluctance transducers we offer at Validyne Engineering have a track record of accuracy and reliability in various environments. Allow our team to guide you in selecting the best pressure transducer(s) for your particular application.

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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