1.0
PURPOSE :
To describe a standard operating procedure for the calibration of Dial temperature
gauges with standard zeal thermometers and the calibration procedure for the
Digital temperature indicator/controllers with standard RTD simulator.
2.0
SCOPE:
The standard operating procedure describes in detail the method for the calibration
of Dial temperature gauges with standard zeal thermometer and Digital
temperature indicator/controllers with standard RTD simulator.
3.0
RESPONSIBILITY:
The responsibility of calibrating the Dial temperature gauges with standard zeal
thermometer and Digital temperature indicator/controllers with standard RTD
simulator lies with the staff of rank not lower than the supervisor of maintenance
department.
The responsibility of preparation, review and approval of the standard operating
procedure lies with the Manager – Maintenance, Head of Production and Head of
QAD respectively.
4.0
METHOD:
4.1
Calibration procedure for Dial temperature gauges with standard zeal
thermometer:
4.1.1
Select a suitable range of standard zeal thermometer, calibration traceability with
national physical laboratory
4.1.2
Heat the oil contained in a bath to the temperature nearer to the maximum
operating temperature of the gauge. Dip standard zeal thermometer and stem of
temperature gauge which has to be calibrated.
4.1.3
Note down 3-4 readings of the standard zeal thermometer and temperature of the
under test gauge.
4.1.4
Similarly, take a chilled bath of temperature to the minimum working temperature
of the gauge and dip the standard zeal thermometer and stem of temperature gauge
which has to be calibrated.
4.1.5
Note down 3-4 readings of the standard zeal thermometer and of the under test
temperature gauge. Record the readings in the format xxxxx as shown in
Annexure-I.
4.1.6
Acceptance criteria:
The resolution of gauge shall be considered as acceptance criteria for that
particular gauge.
 If the gauge is graduated with 1°C resolution, the acceptance criteria shall be
1°C.
 If the gauge is graduated with 2°C resolution, the acceptance criteria shall be
2°C.
 If the gauge is graduated with 5°C resolution, the acceptance criteria shall be
5°C.
4.1.7
Whenever the gauge is rectified or replaced with another before the scheduled
calibration due date, the same shall be informed to the Quality Assurance
Department. Recalibration data shall be recorded as per format xxxxx shown in
Annexure-II and also entered in the history card of the gauge.
4.1.8
The recalibration format xxxxx is also shall be used whenever the gauges
calibrated for validation purpose. The same shall be remarked in remarks column.
4.2
Calibration procedure for Digital temperature indicators / controllers with RTD
simulator.
4.2.1
Select a standard RTD simulator, calibration traceability with national physical
laboratory.
4.2.2
Connect the RTD simulator to the Digital temperature indicator/controller cables
in place of RTD sensor.
4.2.3
Compare the reading of the Indicator/Controller with standard reading labeled on
the simulator by switching ‘ON’ the toggle switch one after the another for 3-4
readings and record the readings in the format xxxxx in Annexure-V.
4.2.4
Acceptance criteria for Digital temperature indicator/controller of range shall be
0.1% of full scale division
4.2.5
Whenever an indicator / controller is rectified or replaced with another before the
scheduled due date of calibration the same shall be informed to the QAD.
Recalibration data shall be recorded in the format xxxx shown in Annexure-VI and
also entered in the history card of the Digital temperature indicator / controller.
4.2.6
The recalibration format xxxxx is also shall be used whenever the
indicators/controllers calibrated for validation purpose. The same shall be
remarked in remarks column.
4.2.7
All the digital temperature indicators/controllers are calibrated by out side agency
in the presence of maintenance department as per the procedure and rectification
of the indicator/controller recalibration shall be carried out by maintenance
department.
4.3
During the calibration, if the dial temperature gauge/digital temperature
indicator/controller does not meet the acceptance criteria, service the gauge,
recalibrate and then inform to the QAD for taking necessary action regarding
variation of the quality and yields of the batches carried out with that
indicator/controller. If the instrument is not possible to repair inside the premises,
send it to the outside agency for necessary repairs. If the indicator/controller is not
serviceable even at out side agency replace the same.
4.4
Apart from the recalibration of instruments, the calibration shall be followed as
per the schedule for all the instruments.
4.5
Calibration tag for Dial / Digital temperature gauge / indicator / controller shall be
tied to the gauge with the following particulars.
CALIBRATION TAG FOR TEMPERATURE GAUGE/INDICATOR
/CONTROLLER
Temperature gauge / indicator / controller No
Location
Calibration / Operating range
Difference
Acceptance criteria
Date of calibration
Next due date of calibration
Calibrated / Recalibrated by
Signature
4.6
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Frequency:
 Calibration of dial temperature gauges shall be once in two months ± 2 days.
 Calibration of digital indicators/controllers shall be once in three months
± 2 days.
5.0
RECORDING:
The responsibility of recording the calibration data as per Annexures lies with the
staff of rank not lower than supervisor of maintenance department.