Oven Calibration
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    NITED STATES DEPARTMENT OF THE INTERIOR   ã  ã BUREAU OF RECLAMATION USBR 1020-89 PROCEDURE FOR CALIBRATING OVENS INTRODUCTION This procedure is under the jurisdiction of theGeotechnical Services Branch code D-3760, Research and Laboratory ServicesDivision, Denver Office enver Colorado. The procedure is issued underthe fixed designation USBR 1020.Thenumberimmediately following the designation indicates the year of acceptance or theyearoflastrevision. 1. Scope 1.1 This designation outlines the procedure for calibrating ovensused for standard laboratory testing.Thiscalibrationprocedure is limited to ovens operating to a maximumtemperature of300 °C. Ovens operating at higher temperatures require special handling and, there- fore, should be periodically checked by the manufacturer. 1.2 This procedure isto be used for periodic checks of laboratoryovens. Ifstringent calibration tolerancesarerequired,thisprocedure should not be usedand ASTM designation: E145is to beconsulted. 2.  pplicableDocuments 2 STM Standard E   STM Thermometers E  45 SpecificationforGravity Convectionand Forced Ventilation Ovens 3. Summary of  etho 3.1 A thermometer is placed in an oven which is set at the desiredoperating temperature. Thetemperaturereading ofthe thermometer is compared to theoven thermostat reading. The appropriate thermostat adjust ment is determined. 4. Significance and Use 4.1Accurate temperature control is important formany soil testing procedures in order to obtainaccurateresults. 4.2 Ovensareusedprimarily for determinationofmoisturecontent in soils. Theovens should haveminimum insidedimensions of 3 feet wide by2 feetdeep by 2 feet high. For mostsoils laboratory applicationovens shouldbe thermostaticallycontrolledat 110___5 °C. Since itis necessary that a uniform temperature be maintained throughouttheoven, the mechanical convection or forced- draftovens arerecommended. NOTE 1.-Ovens slightly smaller than the recommendedsize may be used, but oven temperature variessignificantly when the door is opened, and calibration will be moredifficult. 4.3 Thiscalibrationprocedure is to be performed uponreceipt of theovenandannually thereafter.5. Apparatus 5.1 Oven. An oven, thermostatically controlled, forced-draft or mechanical convection,horizontal airflow type.5.2 Thermometer. Etched stem glass thermometer witheye-hook at the end for hanging, 0 to 300 °C 2 °C divisions, mercury filled, conforming to the requirements ofASTM E 1. 5.3 Gloves. Asbestos pair, to be usedwheneverhandlingequipmentheated to elevated temperatures. 6 Precautions 6 1 Safety recautions 6 1 1 All electrical veires andcords are to be checked for damage If anydamage is observed it is to be repairedbefore attempting to use the oven 6 1 2Care should be exercised inhandling any equipment that is heated to elevated temperatures. Gloves are to be worn whenever handling such equipment or materials. 7. Calibration and Standardization 7.1 Verifythatthe thermometer to be used forthis procedurehas a certificate of inspection or calibrationverification fromthe manufacturer.Ifthere is doubt as to the accuracy ofthe thermometer, it should notbe used for this procedure; a thermometer with a verifiable accuracy is to be obtained and used. 8. Conditioning 8.1 During the calibrationprocedure, the room temperature should notvary more than _ 10 °C. 9. Procedure 9.1 All dataare to be recorded on the  Oven Calibration form asshown on figure 1. 9.2 Locateandrecordthe serial number, or any otheridentifying markings, ofthe oven to becalibrated.42  USBR 1020 9.3 Remove any material  sample containers,pans, etc.)fromthe oven. 9.4 Carefully hang the thermometer by its eye-hook with a pieceof wire as close to the center ofthe ovenchamber as possible. Make surethatthe thermometerhangs freely.9.5 Determine the applicable temperature at whichthe oven willbe calibrated and set the thermostat of the oven to thattemperature. NOTE 2.-For most geotechnicalpurposes theoven willbe calibrated at 110 °C. Ifcalibration is desired at another temperature theprocedure is similar.If a range of calibrated temperatures is desired thecalibrationshouldbe performed in intervals of 5 °C over the desiredrangeof temperatures. 9.6 Allow sufficienttime for theoven temperature to stabilize andrecordthe oven thermostatreading. 9.7 Determine the thermometerreading and recordthevalue. NOTE 3.-The oven temperature will drop drastically whenthe ovendoor is opened. The thermometer reading should be taken as quickly as possible oncethedoor is opened.-   9.9 Calculatethe thermostat correction and recordthevalue. 9.10 If the thermometerreading is within +5 °C of the thermostatreading, the calibrationprocedure is completed.Ifthethermometer readingdiffers fromthe thermostat reading by more than 5   C or if a more stringent calibration is desired, seesubparagraph 1.2. 9.11Adjust the thermostat by the amount of thethermostat correction. 9.12 Repeat subparagraphs 9.6 through9.11 untilthe desired calibration accuracy has been achieved 10. Calculations 10.1 Calculatethe thermostatcorrectionusing thefollowing expression: wh r Thermostat correction =  1)   2) 1) = oventhermostatreading  2) = thermometerreading 11. Report 11.1 Thereport is to consist of a completed and checked  OvenCalibration form  fig. 1). 11.2   calculationsare to show a checkmark. 43  US 2 7 3O6  6-85 ureau of  eclamation Oven Identification Model 1206 SN 36157 Calibration performedbyExomple Calibration checked byExomple OVEN CALIBRATION Designation USBR 1 2 89 Calibration Temperature [] °Cor Temperature Range   D   F Date 3 24   89 Date 3 4 89 OVEN THERMOSTAT THERMOMETERTHERMOSTAT READING READINGCORRECTION  1 2 1 2 II0 °   6 °   6 °   104oc II °C   COMMENTS:  P 847  97 I Figure   Oven calibration   xample.  
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