Category Archives: O-Rings

Selecting Accessories for the Recalibrating the P55 Pressure Transducer

Introduction:
The Validyne P55 pressure transducer has as its sensor a variable reluctance pressure sensor that can 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.

Sensor Parts:
A typical P55 is shown below, with the external parts identified:

P55 Parts pressure transducer

 

 

 

 

First, remove the two Philips head screws holding the sensor to the P55 electronics housing. These are located on the underside of the housing. The wires from the sensor to the electronics are very short, so take care they do not break.

To disassemble a P55 sensor a torque wrench, T27 Torx socket and a vise are needed. The tools needed to disassemble the sensor are available from Validyne and are shown below:

torquewrench pressure transducer

 

 

 

 

 

The sensor can be disassembled by removing 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 pressure transducer

 

 

 

 

 

It is good practice to replace the body bolts and o-rings when changing the range of the P55. 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:

diaphragm pressure transducer

 

 

 

 

 

To re-range a P55 sensor the full scale pressure must be known and the correct diaphragm part number ordered. The part number for a P55 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 P55 sensing diaphragm are shown in the chart below with their full scale pressures expressed in various engineering units.

P55Ranges pressure transducer

 

 

 

 

 

 

 

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. The sensor is reattached to the housing using the two Phillips head screws.

Calibration Accessories:

The next step is to calibrate the P555 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 pressure transducer

 

 

 

 

 

 

 

The T140K calibrator kit is available in six different versions covering the available DP15 full scale pressure ranges. To calibrate theP55 connect it the SI58 digital interface and have a voltmeter to observe the analog output signal of the P55 as it appears on the binding posts of the SI58. 

SI58 pressure transducer

 

 

 

 

 

The SI58 connects to any USB port on a PC and is supplied with software that allows changing the internal registers of the P55 to achieve an accurate calibration. Connect the re-ranged P55 to the SI58 and the SI58 to a PC. Connect a multimeter to the SI58 binding posts to observe the P55 output signal.  

P55Cal pressure transducer

 

 

 

 

Load the calibration software and follow the instructions for applying zero and full scale pressures using the T140K calibrator. The software will adjust the P55 microprocessor correction factors to produce an accurate calibration with the new sensing diaphragm.

The SI58 software also allows the user to compensate the P55 through temperatures. The temperature range can be selected by the user as applied by an environmental chamber. 

SI58 Software pressure transducer

 

Selecting Accessories for the DP15 Variable Reluctance Pressure Sensor

Introduction:

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

Application Note: Selecting O-Ring Material

Validyne transducers and sensors bolt together around the sensing diaphragm. In order to seal the sensor cavity so that pressure can be measured, O-Ring seals are used. The O-Rings come in contact with the fluid inside the transducer so it is important that the fluid and the O-Rings are compatible. Various O-Ring compounds may be specified in the transducer model number to insure that the seal will remain viable when in contact with the fluid during service. This application note will discuss how to select the best O-Ring material for your application.

The standard O-Ring material used in Validyne transducers is Buna-N. This compound is compatible with water, oil and most gases. Since most fluids involved in pressure measurement are usually water or oil-based, Buna-N is normally sufficient. But if you are not sure, it is best to check a compatibility table to select the best O-Ring compound.

The industry standard reference for O-Ring fluid compatibility is the Parker O-Ring Handbook, as published by Parker-Hannifin, manufacturers of O-Rings and fittings. The O-Ring Handbook has an extensive set of tables that give the compatibility of various O-Ring compounds with chemicals commonly used in industry. The O-Ring Handbook is now accessible on line at:

http://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

To use the Parker compatibility tables simply look up the chemical or fluid in question (they are given alphabetically) and determine the compatibility rating of the various available O-Ring compounds.

The Validyne transducer model number designations for the available O-Ring compounds are as follows:

Validyne Model …………. Common Term …………… Parker O-Ring Book Designation
……… N ……………………… Buna-N ……………………………. Nitrile
……… E ……………………… Ethylene Propylene …………… Ethylene Propylene EPDM
……… S ……………………… Silicone …………………………… Silicone MQ
……….T ……………………… Teflon ……………………………… Not Offered by Parker
……… V ……………………… Viton-A ……………………………. Fluorocarbon
……… K ……………………… Kalrez ……………………………… Fluorosilicone

The compatibility designation in the Parker book is 1 through 4 where 1 is considered compatible and 4 is considered unsatisfactory.

Here are some examples:

Fluid: Carbon Dioxide
Compatibility: All of the O-Ring compounds are shown as compatible – Buna-N is a good choice.

Fluid: Brake Fluid DOT 4
Compatibility: Ethylene Propylene is the best choice as it is compatible with the fluid and available as a selection in the Validyne model number.

Fluid: Dichlorobenzene
Compatibility: Fluorocarbon is given as compatible in the Parker table and so Viton-A should be chosen in the Validyne model number. Note that the Parker book shows two different dichlorobenzene compounds, but both are compatible with fluorocarbon.

Teflon is normally a good choice for compatibility with all kinds of fluids but we have found that the lack of elasticity in a teflon O-Ring can cause issues with transducer accuracy and performance. Teflon has a tendency to cold flow over time and this affects the clamping force on the transducer sensing diaphragm. An O-Ring with elasticity is always the better choice and a satisfactory compound can usually be found for all but the most corrosive of fluids.

If the O-Ring in the sensor is not compatible with the fluid, the first sign will probably be leaking or even complete loss of pressure. Disassemble the sensor and inspect the O-Rings for swelling and replace with a compatible compound. Validyne offers O-Rings separately for each model transducer or sensor and these are usually in stock. You can find more details on O-Rings here.

o-ring material