Definition - Pressure

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1 Definition - Pressure F P = A Pressure Force = Mass x Acceleration Area SI Unit Pascal = Newton/m 2 = (m kg s -2 )/m 2

2 Influences on Force Σ F P = A Mass Load Local Gravity Air Buoyancy Verticality (Level) Surface Tension Other (Environment) -- Magnetism, Air Drafts, Mass Rotation

3 Influences on Area F P = A Pressure Dependence Distortion Operating Fluid Geometric Uniformity Temperature

4 Reference Modes

5 ACCURACY TERMS

6 LINEARITY TSL O/P Draw a line through zero and full scale pressure point Error is either positive or negative Typically nearly twice the BSL fig ure P

7 LINEARITY BSL O/P Draw a best straight line th rough all the points (least square error) Error is + and - P

8 FORCED ZERO BSL O/P Fix the zero Slope is BSL P

9 REPEATABILITY Definition - the spread of readings when taking consecutive measurements without changing the pressure, temperature or other external environmental conditions e.g. EMC This is not easy to measure because the noise is masked b y changes in the environmental factors Our best estimate comes from noise measurements which give <<0.1 uv in the frequency range 0.1 to 10 Hz.

10 PRESSURE HYSTERESIS The changes in measured pressure as a percentage of full s cale when the pressure is changed then returned to the orig inal value whilst keeping all other environmental conditions the same or compensating for them. Again difficult to measure, changing pressure changes the t emperature of the pressure media. Current design show pressure hysteresis lower than our m easurement threshold.

11 TEMPERATURE ERRORS TEB (Thermal error band) RTE (Referred temperature error) Thermal hysteresis Good design and temperature cycle out hyster esis Creep

12 RTE: REFERRED TEMPERATURE ERROR Error is with respect to the room temperature error Not necessarily a linear relationship.

13 TEB: TEMPERATURE ERROR BAND Measure performance at all temperatures Plot all errors and put a band around them, take the spread say 2%Fs and h alve the figure quoting +/-1%FS TEB

14 Why Calibrate? Every day we make decisions based on the information we have acquired. Whether we make the right decisions depends largely on whether the information is correct. We often acquire information by way of measurement.

15 Equipment Categories Product Critical Instruments - have a direct effect on QUALITY Process Critical Instruments - have a direct effect on QUANTITY Safety Critical Instruments - have a direct effect on plant and personnel SAFETY Non Critical Instruments

16 Calibration Hierarchy NATIONAL STANDARDS LAB International/National Primary Standard & Secondary Standard CALIBRATION LABORATORY Reference Standard & Working Standard INDUSTRY Industrial Standard & Measuring Device

17 PRESSURE STANDARDS 1. Primary Pressure Standard : -. Dead weight Tester ex) Model : 2465 ( RUSKA) 2. Secondary Pressure Standard -. Portable Pressure Calibrator ex) DPI 610 series, DPI605 series -. Digital Pressure Controller ex) DPI 515, DPI520, 7250 series.

18 PRESSURE CALIBRATION MEASURING INSTRUMENTS DRIFT PRODUCTION QUALITY ISO 9000 TRACEABILITY OF ALL MEASUREMENTS WHY CALIBRATE? PRODUCTION COST LEAKAGE PLANT FAILURE SHUT-DOWN SAFETY

19 WHY USE A DEADWEIGHT TESTER? PRIMARY REFERENCE FOR PRESSURE. MOST ACCURATE AND STABLE MEANS OF PRESSURE MEASUREMENTS. DIRECTLY TRACEABLE TO INTERNATIONAL PRESSURE STANDARDS. SELF-CONTAINED WITH OWN PRESSURE GENERATOR (NOT HIGH PRESSURE AIR MODELS). ISO 9000 SHORTSIGHTED TO BUY EXPENSIVE ACCURATE PRESSURE SENSING DEVICES WITH NO MEANS TO CHECK OR VERIFY ACCURACY. SAVE MONEY BY HAVING THE ABILITY TO CALIBRATE OWN SECONDARY STANDARDS USE OF EXTERNAL LABORATORIES LOSE USE OF INSTRUMENT FOR LONGER RISK CHANGE IN STATUS AFTER CAL SAVE MONEY BY HAVING VERY ACCURATE MEASUREMENTS : FISCAL METERING / CUSTODY TRANSFER INTRINSICALLY SAFE

20 TYPES OF DEADWEIGHT TESTER DEADWEIGHT TESTERS PRIMARY STANDARDS SIMPLE TO USE STABLE ACCURATE INTRINSICALLY SAFE ACCURACY FROM:0.005% to 0.1% OF READING SPECIFICATIONS AVAILABLE RANGES FROM:-1 to 4000 bar OPERATING MEDIA:OIL, GAS, WATER OPERATING ENVIRONMENT: LABORATORY, INDUSTRIAL, ON-SITE PRESSURE MODES POSITIVE GAUGE PRESSURE NEGATIVE GAUGE PRESSURE ABSOLUTE PRESSURE DIFFERENTIAL PRESSURE

21 GAUGE PRESSURE FORCE AREA PRESSURE PRESSURE = FORCE AREA

22 VACUUM VACUUM AREA FORCE

23 ABSOLUTE PRESSURE REFERENCE PRESSURE (RP) FORCE VACUUM PUMP AREA ABSOLUTE PRESSURE = FORCE AREA + RP

24 DIFFERENTIAL PRESSURE P DIFFERENTIAL PRESSURE TRANSMITTER HIGH LOW BALANCE PISTON MEASURING PISTON CROSS CONNECTING VALVE

25 WHICH DEADWEIGHT TESTER? WHAT PRESSURE RANGE IS REQUIRED? WHICH DEADWEIGHT TESTER? WHAT OPERATING MEDIA IS REQUIRED? WHAT ACCURACY IS REQUIRED?

26 WHICH DEADWEIGHT TESTER? WHAT MEDIA? GENERALLY: HIGH PRESSURES HYDRAULIC LOW PRESSURES PNEUMATIC The deadweight tester is accurate whilst the piston and weights are floating and spinning. The piston must spin to eliminate friction. Oil deadweight testers will not spin at low pressures due to the drag of oil. OIL 1 to 4000 bar ROBUST GOOD LUBRICANT LARGE GAP BETWEEN PISTON & CYLINDER TOLERATE SMALL DEGREE OF CONTAMINATION (NOT RECOMMENDED) LITTLE USER MAINTENANCE REQUIRED WATER 0.5 to 700 bar GAS to 140 bar CARE REQUIRED GREATER CARE REQUIRED POOR LUBRICANT SMALL GAP BETWEEN PISTON & CYLINDER ENSURE WATER FILM EXISTS AROUND PCU BEFORE USE DISTILLED / DEIONISED WATER ONLY DO NOT CONTAMINATE PERIODICALLY CLEAN PCU POOR LUBRICANT SMALLEST GAP BETWEEN PISTON & CYLINDER DO NOT CONTAMINATE GAS SUPPLY MUST BE CLEAN & DRY DEVICE UNDER TEST MUST BE INTERNALLY CLEAN FREQUENTLY CLEAN PCU

27 WHICH INSTRUMENT? W H A T A C C U R A C Y? IF U N C E R T A IN, U S E T H E R U L E O F T H U M B : 10 TIMES MORE ACCURATE THAN THE DEVICE TO BE CALIBRATED IF A MANUFACTURER 4 TIMES MORE ACCURATE THAN THE DEVICE TO BE CALIBRATED IF AN END USER 2% 1% 0.5% BOURDON TUBE PRESSURE GAUGE COMPARITOR 0.25% ELECTRONIC TRANSFER STANDARD 0.1% 0.05% 0.025% DEADWEIGHT TESTER 0.01%

28 ENVIRONMENTAL INFLUENCES PRESSURE = FORCE AREA FORCE AREA PRESSURE INFLUENCE STANDARD / REFERENCE VARIANCE / EFFECT GRAVITY (FORCE) cm/s² 0.5% TEMPERATURE (AREA) 20 C %/ C A IR DENSITY (FORCE) g/ml % / NOTE: AIR DENSITY VARIES TYPICALLY FROM TO g/ml A LL OF THE ABOVE INFLUENCES CAN BE COMPENSATED FOR.

29 LOCAL GRAVITY 1. SITE SURVEY 2. GRAVITY CALCULATION THE CALCULATION IS BASED UPON THE FOLLOW ING DATA: SITE LATITUDE IN DEGREES (L) SITE ALTITUDE IN METRES (H) THE EQUATION USED FOR SEAL LEVEL IS AS FOLLOWS: LOCAL GA = ( x cos2l x 10-6 x cos2l x cos2l) THE EQUATION USED FOR HEIGHT ABOVE SEA LEVEL IS AS FOLLOWS: FOR EXAMPLE: LOCAL GRAVITY = GA x H SITE LATITUDE IN DEGREES (L) = SITE ALTITUDE IN METRES (H) = 100 LOCAL GRAVITY AS CALCULATED ABOVE = cm/s² 1. NEAREST LOCAL SITE THE FOLLOWING GENERALLY HAVE LOCAL SITE GRAVITY SURVEYS: METROLOGY INSTITUTE UNIVERSITY AIRPORT

30 PISTON GAUGE SELECTION CHART Accuracy: < 0.01% No See Pressurem ents Deadweight Gauges Yes Media: O il Gas Both A utomatic O il o r A u to m atic Manual Model ,000 psi M axim um B Manual o G as t h Pressure Range: No 20,000 psi Model 2485 High Pressure System 72,500 psi Range Select Any Piston Assy. Y es Pressure Range: 1,000 psi No Yes M odel ,000 psi Gauge & Abs. Model 2485 Low Pressure System Select Piston Assy. 10 1,000 psi ,000 psi ,000 psi Pressure Range: 3,000 psi Yes M odel ,000 psig M odel System G as to 15,000 psi O il to 20,000 psi Select Any Piston Assy. to 20,000 psi No M odel ,000 psig H eliu m G as

31 Ruska 2465 Gas Piston Gauge

32 Model 2485 Hydraulic DWG

33 2485 Key Features Accuracy % of Reading to 70 bar % of Reading to 1400 bar 0.01% of Reading to 5000 bar Protected Piston/Cylinder Design Easy to Install Piston/Cylinder - No Tools Required Easy to Operate (Isolation Valve, 3 Point Level)

34 Secondary Standards

35 WHAT IS A CONTROLLER/CALIBRATOR? Secondary or transfer standard Visual display of controlled pressure output Electrical input/output Digital input/output Pressure output

36 BASIC CONCEPT OF A PRESSURE CONTROLLER Source Input Output Device Under Test Setpoint + - Pressure Controller Feedback

37 DRUCK CONTROLLERS/CALIBRATORS DPI 515 DPI 520 DPI 530

38 DPI 515 MAIN FEATURES 0.01% FS Precision (0.03% FS below 700 mbar) 0.02% Reading 12 month measurement stability Wide choice of pressure ranges 25 mbar FS to 210 bar FS RS232 and IEEE-488 comms as standard Fast control to setpoint, typically less than 10 seconds Control stability better than 10 ppm at setpoint Easy to learn, user friendly interface

39 DPI 515 AERONAUTICAL OPTION C Control in Aerospace units feet, metres, Knots, Km/h, Mph or Mach Altitude control/measure to 0.13 mbar Airspeed control/measure to 0.2 mbar Timed or instant Rate of Climb Settable R.O.C. and rate of speed to protect sensitive instruments Compatible with current RVSM requirements for Altitude Different configurations available (C1: Altitude, C2: Airspeed, C3: Both)

DPI 515-2892 NATO CODIFIED Special 5 range version Primary manifold - 35 bar g/36 bar abs (Engine pressure) - 750-1150 mbar abs (Barometric ref.) Secondary manifold - 2.5 bar gauge (Airspeed) - 1.

40 DPI NATO CODIFIED Special 5 range version Primary manifold - 35 bar g/36 bar abs (Engine pressure) mbar abs (Barometric ref.) Secondary manifold bar gauge (Airspeed) bar absolute (Altitude) bar differential All Aeronautical ranges on one manifold Includes soft carry case and user manual Calibration and service manuals available Fully NATO codified (NSN ) 300 bought by UK MOD for RAF

01% Utilises Druck RPT as control sensor, (no zeroing required!

41 DPI 515 ENHANCED STABILITY OPTION E Absolute pressure control to 0.01% FS mbar abs mbar abs mbar abs 12 month measurement stability 0.01% Utilises Druck RPT as control sensor, (no zeroing required!) Replaces the old DPI 501 for low pressure absolute application E1: Single range, can be combined with any other range/option E2: Dual range, available with any option except the barometric reference (A)

42 LABVIEW DRIVER FOR DPI 515 Free Labview 6.0 Driver and example VI available at Easy interface with PC via Labview IEEE or RS232 compatible

43 LABVIEW SCHEMATICS

44 LABVIEW VIRTUAL INSTRUMENT

45 DPI 515 SENSOR CALIBRATION MODULE Units Accurate electrical measurement of sensor outputs Pressure Window mbar Vent Pressure Set Point SCM Window Set point: mbar Rate:Or Pre-Set/Divider SCM: mva Range Process Gauge/abs Range Auto Range SCM 1barg 135mVA 135mVC Ranges 0-25 ma, ± 135 mv, 0-11V 7barg V 25nA SCM Off Excitation output +10 V reg, +24 V unreg Basic task modified with SCM feature More Integral to DPI 515, all in one pressure calibration Easy connection with special SCM lead and probe Dual screen display of pressure and electrical values

46 DPI 515 SOFTWARE UPGRADES New software in development for improvement Downloaded via RS232 Present release 4.3 Next release 5.0, due early 2002 Includes: Improved control Jog in Divider/Present Tasks Test programs (similar to RUI 100 on DPI 520). Stores 15 programs

DPI 515 TECHNOLOGY Utilises Druck PDCR 2200 low doped grade A sensor Fully temperature characterised to provide enhanced performance Barometric reference via Druck RPT Highly reliable internal PSU,

47 DPI 515 TECHNOLOGY Utilises Druck PDCR 2200 low doped grade A sensor Fully temperature characterised to provide enhanced performance Barometric reference via Druck RPT Highly reliable internal PSU, same as DPI 520 (excellent MTBF) Manifolds machined from a single block of metal with latest pick n place, surface mount technology Extruded aluminum chassis and steel plates for body strength Moulded ABS front panel for ergonomically pleasing look and mechanical strength

48 DPI 515 APPLICATIONS

49 DPI 520 APPLICATIONS

Pressure calibration. 20

Pressure calibration. 20 Pressure calibration Pressure calibration is the comparison of the output of a device used to measure pressure with that of another pressure measurement device, or pressure measurement standard. This usually