Tag Archives: variable reluctance

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.

Selecting the Best Validyne Carrier Demodulator

Carrier Demodulator

A carrier demodulator is the electronics that supports a variable reluctance pressure transducer. A carrier demodulator provides power to the transducer, provides calibration adjustments, receives the AC sensor signal and converts it to a useable output. What is the best carrier demodulator to use with your variable reluctance pressure transducer? The answer to that question depends on a number of factors.


Do you need a digital display in units of pressure? The CD23 provides an LED display which can be read from several feet away. The CD379 has a liquid crystal display. If a digital display is not needed, then the basic CD15 is probably sufficient.


Is 110 VAC available? Most Validyne carrier demodulators have a version that will run on standard 110 VAC power. For portable use, the CD379 is battery operated.


Looking for the lowest cost? The CD101 is a carrier demodulator circuit board. Add your own
enclosure and power supply for a custom solution.

High Gain:

The CD12 provides selectable gain settings up to 20 times higher than the standard demodulator.  Combined with the zero suppression feature, the CD12 allows observation of small pressure variations that are riding on high static pressures.


If you have several transducers, then a multi-channel carrier demodulator such as the CD280 or MC1 system may be the most cost-effective carrier demodulation.

Computer Interface:

Do you want the signal to go into a PC? The CD17 is a USB interface for a single variable reluctance sensor.  Up to 16 variable reluctance transducers can be supported by the UPC2100 PCI plug-in card or the USB2250 for USB interface to laptops. These card include complete carrier demodulation and A/D conversion as well as scale and offset factors for conversion into engineering units.

carrier demodulatorFind data sheets and instruction manuals on the products listed above www.validyne.com/carrier demodulator

Selecting Accessories for the DP15 Variable Reluctance Pressure Sensor


The Validyne DP15 variable reluctance pressure sensor is distinguished by its ability to be re-ranged for different full scale pressure measurements. The sensor can be disassembled, a new sensing diaphragm installed and the unit re-calibrated to the new full scale pressure. Some 23 different full scale pressure diaphragms are available and this application note will describe how to select and order the parts needed to re-range the sensor and interface the signal to a PC.

Accessory Sensor Parts:

A typical DP15 is shown below, with the replaceable external parts identified:

dp15parts variable reluctance pressure sensor





To disassemble a DP15 a torque wrench, T27 Torx socket and a vise are needed. These items are available from Validyne and are shown below:

torquewrench variable reluctance pressure sensor






The sensor can be disassembled by removing the two top screws holding the connector and then the four 10-32 Torx T27 body bolts. When disassembled, the sensor body pieces separate and the sensing diaphragm and o-rings are removed. These parts are shown below:

boltsorings variable reluctance pressure sensor






It is good practice to replace the body bolts and o-rings when changing the range of the DP15. Various o-ring compounds are available (see ordering chart).

The sensing diaphragm may now be replaced with one of a different range. A typical sensing diaphragm is shown below:

diaph-2 variable reluctance pressure sensor




To re-range a DP15 sensor the full scale pressure must be known and the correct diaphragm part number ordered. The part number for a DP15 diaphragm starts with 3- and is followed by a two-digit range code. The diaphragm in the photo above is p/n 3-22 and has a full scale range of 5.5 In H2O. The other available range codes for the DP15 sensing diaphragm are shown in the chart below with their full scale pressures expressed in various engineering units.

P55Ranges variable reluctance pressure sensor









Re-assembly is simply the reverse of dis-assembly, taking care that the torque on the body bolts is 125 In-Lb. The vise is used to stabilize the sensor body during assembly and to allow the torque to be correctly transmitted to the body bolts.

Also be sure that the bleed screws are tightly seated – these use a 5/64” hex wrench, Validyne p/n K950-0781.

Calibration Accessories:

The next step is to calibrate the DP15 against a pressure standard. Validyne can supply model T140K calibrator kit that includes a pressure pump and reference standard – an example is shown below.  

T140K variable reluctance pressure sensor







The T140K calibrator kit is available in six different versions covering the available DP15 full scale pressure ranges. To calibrate the DP15 connect it to your carrier demodulator and have a way to observe the output signal of the demodulator. In the example below a CD15 basic carrier demodulator is used with a DP15 and T140K:

caldiagram variable reluctance pressure sensor





The Zero and Span adjustments on the CD15 are set during the calibration process so that the analog output is 0 to +/-10 Vdc.

PC Interface Accessories:

The DP15 is typically used in a laboratory where pressure measurement requirements often change. Other sensors may be required to make measurements and the mix and combination of these sensors may also vary. Validyne makes several PC-based data acquisition products that accept any combination or mix of sensor types including thermocouples, strain gages, LVDTs, resistances, RTDs, potentiometers, DC volts and variable reluctance pressure transducers like the DP15.

The DP15 and other sensors can be connected to a PC using the Validyne UPC/USB series of products:

UPC-USB variable reluctance pressure sensor





The UPC2100 (left) is a PCI plug-in card for desktop PCs and the USB2250 (right) is a self-contained box that connects to the USB port on a laptop PC.

Both interface devices accept any combination of sensor inputs in addition to DP15 transducers. These products supply all required sensor excitation, amplification, demodulation and A/D conversion. A terminal block is used to receive the field wiring from the sensors and this is connected by a ribbon cable to the UPC2100 or USB2250. The terminal block and ribbon cable is included.

Easy Sense software is also included and this allows the user to configure each of the 16 input channels for different sensor types and to do data logging to a disk file that can be opened by Excel. Both the USB2250 and UPC2100 support 16 bit resolution, six programmable gain ranges and 50,000 sample/second data throughput.

Easy Sense Premium software is available that also includes a graphing function. LabView is supported and programming in Visual Basic.

The cable for connecting the DP15 to the USB2250 or the UPC2100 is Validyne p/n 12457-10.  

UPCCable variable reluctance pressure sensor




Another method of interfacing a single DP15 to a PC is the Validyne CD17. This connects to the transducer using a standard transducer cable (Validyne p/n 11264-10) and comes with a USB cable for connection to a laptop or other PC.  

cd17_5_480 variable reluctance pressure sensor





The CD17 produces readings in mV/V and comes with configuration software that will also log data to a text file compatible with Excel. A premium version of the software allows graphing.

Solo61 variable reluctance pressure sensor








partslist variable reluctance pressure sensor