Category Archives: velocity

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

 

Instrumenting Curtain Wall Tests

Validyne Products: DP103, USB2250

Curtain walls are the outside glass coverings of skyscrapers and large buildings. A curtain wall allows floor-to-ceiling windows and provides a shiny exterior to the building. Older buildings had windows that were openings in the wall structure. Curtain walls are so named because they are hung away from the structural part of the building – like curtains – and bear no structural load. The curtain wall must withstand the outside elements: wind, rain and temperature extremes and so curtain walls must be tested prior to being installed on a large building. This application note details a procedure for curtain wall tests.

The standard test sequence is to build a sample section of the curtain wall and expose it to wind and rain generated at the test facility. This sequence of photos shows what this looks like.

Installing the sample curtain wall section on a scaffold.

curtainwall-5 curtain wall tests

 

 

 

Bringing up the wind machine.

curtainwall-2 curtain wall tests

 

 

 

 

 

 

 

Blowing air and water at the sample.

curtainwall-3 curtain wall tests

 

 

 

 

 

The idea is to simulate the worst predicted weather for a given location and verify that the curtain wall design is robust enough to survive. The curtain walls are instrumented so that the deflection of the glass sections that make up the wall can be measured at different wind force loads.

The deflection is measured with a lanyard potentiometer. This is a displacement sensor that resembles a tape measure – a length of cable extends out from the lanyard pot that is spring loaded. The cable is wound around a spring-loaded potentiometer so that as the cable move the resistance of the potentiometer changes.

The wind loading is measured by a DP103 pressure transducer connected to the outside of the test section. A sensitive transducer is used because even a lot of wind velocity does not generate a very high pressure. Air moving at 100 MPH, for example, generates about 4.8 In H2O of pressure. A DP103 can be used to measure this and much lower pressures if needed.

Both the lanyard potentiometer and the DP103 transducer can be interfaced to a computer using the Validyne USB2250. This will provide the DC excitation required for the lanyard pot and the AC excitation needed for the DP103 sensor. The USB2250 will provide digital readings in In H2O for the DP103 and inches of deflection for the lanyard pot. These readings can be recorded in Easy Sense software and correlated so that the window glass can be evaluated for the conditions simulated during the test.

The sketch below shows the actual wiring connections for these sensors to the USB2250:

curtainwall-1 curtain wall tests