CALIBRATION OF ORP TRANSMITTER

1.0    PURPOSE:

    To describe a standard operating procedure for calibration of ORP (Oxidation Reduction Potential) transmitter. 
    
2.0    SCOPE:

    The standard operating procedure describes in detail the method for calibration of ORP transmitter.
    
 3.0    RESPONSIBILITY:

    The responsibility of calibrating ORP transmitter lies with the staff of rank not lower than chargeman of maintenance department.

The responsibility of preparation, review and approval of the standard operating procedure lies with the Executive - Maintenance, Manager – Maintenance, General Manager (Production) and Head of QAD respectively.
    
4.0    METHOD:

4.1.    Electronic Calibration using a Milli volts Calibrator and Multi meter: 

4.1.1    Ensure that Multimeter and Milli volts Calibrator used for the calibration are precalibrated with traceability to national standards. 

4.1.2    Disconnect the ORP meter sensor wires from the ORP transmitter.
4.1.3    For ORP range of -1200 mV to +1200 mV, connect the Milli volts calibrator to ORP transmitter.

4.1.4    Disconnect the ORP indicator wires from the ORP transmitter.

    
    
4.1.5    Connect the Multimeter to the ORP transmitter to indicate the 4 to 20 mA DC output.

4.1.6    Generate - 1200 mV input signal from the Milli volts calibrator and adjust span control of Multimeter for 4 mA DC output.

4.1.7    Generate + 1200 mV input signal from the Milli volts calibrator and adjust span control of Multimeter for  20 mA DC output.

4.1.8    Set back the input signal to - 1200 mV, confirm that the Multimeter display indicates 4 mA DC output. And also at +1200 mV input signal ensure that the Multi meter display indicates 20 mA DC output.

4.1.9    Generate and apply the input of -1200 mV, -600 mV, 0.000 mV, +600 mV, +1200 mV with the help of calibrated Milli volts calibrator to ORP transmitter and check the output current in mA DC with the help of calibrated Multimeter. Record the readings as per the Format No. xxxxx as shown in Annexure-I.

4.1.10    Standard chart for Milli volts (input) Vs specified Milli Amps (output) shown in Annexure-III.

4.1.11    Find the difference between specified input current and measured output current and record the same in the format as shown in Annexure-I.

4.1.12    Acceptance criteria: ± 0.1%. FSD (-1200 mV to +1200 mV range).

4.1.13    If the ORP reading shows difference within the acceptance range, a tag showing the status of the ORP transmitter shall be tied to the ORP transmitter.

4.1.14    During the calibration, if the ORP transmitter does not meet acceptance criteria, service the ORP transmitter, recalibrate by informing to the QAD and record the readings as per Format No. xxxxx as shown in Annexure-II.

    
4.1.14    Even after servicing, if the ORP transmitter does not meet the acceptance criteria the ORP transmitter shall be replace with new.  Replacement data shall be recorded in the history card.

4.1.15    Whenever the ORP transmitter is rectified or replaced with another, the same shall be informed to QAD.  Recalibration data shall be recorded shown in Annexure-II and also to be entered in the history card.

4.1.16    Apart from the recalibration, the calibration shall be followed as per the regular schedule.

4.1.17    The ORP transmitter which is out of order shall be sent for repairs to outside agency.

4.1.18    Calibration tag shall be tied to the ORP transmitter with the following particulars.

4.1.19    Frequency: Calibration shall be carried out once in six months ± 15 days.
    
5.0    RECORDING:  
                                       
    Record the details of ORP transmitter calibration/recalibration as per Annexure-I and Annexure-II lies with the staff of rank not lower than the Jr. Engineer of maintenance department. 

Orp transmitter, engineering, dc output