i• • UNITED STATES DEPARTMENT OF THE INTERIOR.- ,• BUREAU OF RECLAMATION

USBR 1050-89PROCEDURE FOR

CALIBRATING PRESSURE TRANSDUCERS

INTRODUCTION

This procedure is under the jurisdiction of the Geotechnical Services Branch, code D-3760, Research and Laboratory ServicesDivision, Denver Office, Denver, Colorado. The procedure is issued under the fixed designation USBR 1050. The number immediatelyfollowing the designation indicates the year of acceptance or the year of last revision.

1. Scope1.1 This designation outlines the procedure for

calibrating pressure transducers.1.2 This calibration procedure is used to determine tile

accuracy of pressure transducers over the full pressure rangeas set forth in the manufacturer's specifications.

2. Auxiliary Tests

2.1 The pressure gauge used in this procedure mustbe calibrated in accordance with USBR 1040 prior toperforming this calibration procedure.

3. Applicable Documents

3. l USBR Procedures:USBR 1040 Calibrating Pressure GaugesUSBR 3900 Standard Definitions of Terms and SymbolsRelating to Soil Mechanics

4. Summary of Method4.1 A pressure transducer and a standard pressure

gauge are connected to a pressure source. Pressure is appliedin predetermined increments over the full range of thepressure transducer. The pressure transducer voltage outputis compared at each increment to a pressure gauge reading.The percent error of the pressure transducer whencompared to the pressure gauge reading is calculated foreach pressure increment over the full range calibrated. Fromthese percent error values, a determination is made to acceptor reject the pressure transducer for laboratory use.

5. Significance and Use

5.l A calibrated pressure transducer must be used inthe laboratory to ensure reliable test results.

5.2 This calibration procedure is to be performed uponreceipt of the pressure transducer and annually thereafter.

6. Terminology

6.1 Definitions are in accordance with USBR 3900.6.2 Terms not included in USBR 3900 specific to this

designation are:6.2.1 Hermetically Sealed.-A process by which a

device is sealed and guaranteed to be airtight.

6.2.2 Pressure Transducer.-An electronic transducerthat translates changes in pressure into changes in voltage.This change in voltage produces, in the readout system,a repeatable signal or indication that can be calibrated interms of pressure applied to the transducer.

6.2.3 Readout System.-An electronic apparatuswhich accepts the output signal from a signal conditionerand converts it into a display and a record of the outputsignal.

6.2.4 Signal Cooditioner.-An electronic apparatusnecessary to make the output signal from a transducercompatible with the readout system. It also provides theexcitation for a passive transducer element, such as apressure transducer.

6.2.5 Traceability Certificate.-A certificate ofinspection certifying that a measurement device meets theFederal specification for its particular grade or model andwhose accuracy is traceable to the National Institute ofStandards and Technology (National Bureau of Standards)or an International Standard.

7. Apparatus

7.1 Pressure Transducer (fig. 1).-A transducer whichconverts a pressure input into an electrical output.

7.1.1 Components of the pressure transducer musthave the following characteristics:

7.l.1.1 Electrical parts of the transducer must behermetically sealed to prevent damage to internalcomponents in the event of exposure to moisture.

7.1.1.2 The transducer must be threaded withappropriate threaded fittings to attach the transducer tostandard pipe fittings.

7.1.1.3 Cable connections must be securelyfastened to the body of the transducer.

7.2 PressureGauge.-A bourdon tube air pressure gaugewhose range equals or exceeds that of the pressuretransducer being calibrated is to be used. The gauge musthave a current calibration accompanied with a certificateof traceability.

7.3 Pressure Source.-An air pressure source capableof delivering and maintaining pressure up to the maximumrated pressure of the transducer is required.

7.4 Readout System.-A voltmeter or a computer mustbe used to provide a visual display of the signal beingsent from the signal conditioner.

•'•2

USBR 10511,

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USBR 1050

12. Calculations

12.1 Determine pressure transducer error for eachpressure increment.

Error = applied pressure - readout response

12.2 Determine percent error for each pressureincrement.

( error )Percent error = 100 applied pressure

13. Report

13.1 The report is to consist of a completed and checked"Pressure Transducer Calibration" form (fig. 2).

13.2 All calculations are to show a checkmark.

14. BackgroundReferences

Electrical Transducer Nomenclature and Terminology,ANSI, ISA-$37.1, Research Triangle Park, North Carolina,December 1982.Specifications and Tests for Strain Gage PressureTransducers, ANSI, ISA-$37.3, Research Triangle Park,North Carolina, December 1982.

84

USBR 1050

7-2307 (6-85)Bureau of Reclamation

PRESSURE TRANSDUCER CALIBRATION

Manufacturer ExQmple

Calibrationperformed by

Calibrationchecked by

Serial No. 14385

Designation USBR 1050- 89

Range 0- 7000kPo

Date

Date

Trial Number

2

Appliedpressure

( kPo )

0

Readoutresponse

( kPo )

6890

Error

( kPo )

0

6882

Error

%

0172 172 0 0

345 345 0 0

517 517 0 0

689 688 I 0.15861 860 I 0.12

1034 1033 I O. lO

1206 1204 2 0.17

1378 1376 2 0.15

2067 2064 3 0.15

2756 2753 3 0.113445 3441 4 0.12

4134 4129 5 0.12

4823 4817 6 0,12

5512 5505 7 0.13

6201 6194 7 0,11

8 0.12

0 0 0 0

•EMARKS

Figure 2. - Pressure transducer calibration - example.

G PO 847 -- 972

85