Calibration of O2 Trace analyzer

Table of Contents

This Article establishes the minimum guidelines for E&I Technicians and/or contractors to perform the calibration of O2 Trace analyzer. This document also enable E&I technicians to do primary level configuration and troubleshooting.

Scope and Responsibility

This document is applicable for Trace O2 analyzer (Servomex 4100 Series).

E&I Technicians are responsible to follow the steps as mentioned in this procedure.

E&I Manager and Instrumentation Engineers are responsible for the implementation of this procedure.

Competency Requirements

E&I Technicians must be trained and qualified to perform calibration of Trace O2 analyzer.

Definition

Trace O2 analyzer is based on Zirconia cell Technology. These are used in a process industry for continuous measurement of O2 concentration in ppm. It is mandatory to calibrate them at regular intervals of time, so that there may not be any interlock failure.

The low calibration gas must be a high quality certified mixture of pure background gas (usually nitrogen n6.0) containing trace oxygen. Mixtures containing between 100 and 1000vpm oxygen are preferred, however, lower concentrations may be used.

The high calibration gas must be pure dry air containing 209500vpm oxygen (i.e. 20.95% volume)

References

Procedure Requirement

Sample Requrement

For the best performance the flow, or pressure, supplied to the analyzer should be kept at a constant value for both normal sampling and for calibration gas input.

Temperature	5 to 40°C / 41 to 104°F
Dew point	5°C / 9°F below minimum ambient
Condition	Oil free, non – condensing, filtered to 2μm
Vent	Each sensor outlet should be connected to a separate Atmospheric vent, free from any back-pressure. (Consideration should be given to the toxicity and Asphyxiant nature of the sample gas when selecting a vent location)
Flow driven options	For Zr: 200 (min) – 550 (max) ml/min
Pressure driven options	Nominal- 5psig/ 35kPa Range- (2psig/14kPa to 8psig/56kPa)

WARNING

This analyzer (4102C and 4104C) is not suitable for use with flammable or corrosive samples.

Internal autocal is unsuitable for use with toxic samples.

If toxic samples are present, the maximum pressure to the analyzer must be limited to 8psig by means of a suitable pressure release system.

CAUTION

Do not exceed the rated flow or pressure as sensor damage may result

SAFETY PRECAUTIONS

Ensure that tools necessary for performing the task are being used.
If the analyzer is an EIS, take necessary precautions for maintenance of EIS.
Wrong implementation of procedure/implementation without proper communication may lead to accidents or cause of plant trip.

CALIBRATION FREQUENCY-

4 Weekly

CALIBRATION PROCEDURE

Proper procedure is necessary to ensure the satisfactory operation.

Ensure the Work order (print copy after WO released) is ready to perform the calibration on Analyser.
Ensure the work permit/Maintenance request form to perform
Put the Analyzer in CAL mode by changing the position of selector switch from Run mode to Cal mode in Analyzer panel.
Connect the Zero Gas cylinder and Span gas cylinder and ensure respective sample tapings; as it varies according to the range of the analyzer
Open Zero gas cylinder (100 to 1000vpmO2, Bal N2) and regulate the set pressure at 0.5 barg (max.) and take it inline for analyser sampling.
Set the flow in rotameter within the limit of (200 to 550)ml/min.
Now purge the analyzer for some time until the displayed value to be stable.
If a considerable difference is observed in zero value then proceed with calibration. Go to Main menu and choose the calibration option. Push the calibration button and enter the password as 4000 using arrow keys.
Select the manual calibration from the option available. Choose low calibration option and enter low calibration target according to certified accuracy of gas. Once low calibration target is entered then it will prompt for yes/no. Choose yes and press enter. Now wait for few seconds until it shows calibrated value.
Now Zero calibration is over.
Release the pressure by moving the regulator knob anticlockwise and close the zero gas cylinder using cylinder key.
Open the Span gas cylinder (209500vpm, Bal N2), set pressure to 0.5 barg (max.) and put span gas inline with the analyzer.
Set the flow in Rotameter within the limits of (200 to 550)ml/min.
Purge the analyzer with same gas for some time and observe the value in the analyzer till it becomes stable.
If there is considerable difference is observed in span value then proceeds with calibration. Go to Main menu and then choose the calibration option. Push the calibration button and enter the password as 4000 using arrow keys.
Select the manual calibration from the option available. Choose low calibration option and enter low calibration target according to certified accuracy of gas. Once low calibration target is entered then it will prompt for yes/no. Choose yes and press enter. Now wait for few seconds until it shows calibrated value.
Span calibration is over.
Release the line pressure by moving the regulator knob anticlockwise and close the span gas cylinder using cylinder key.
Now take the process sample inline to the analyzer.
Remove the analyzer from CAL mode.
Hand back the work permit/ Maintenance request form & close Work order.

Replacing The Sample Filter Element

The front panel sample filter elements should be replaced every six months. External filter elements may be replaced annually or more frequently if necessary. Procedure is as follows-

Stop sample flow to analyzer.
Use spanner (provided for front panel filter) to unscrew sample filter cap. Support the body of the external unit as necessary.
Remove old filter element and, on front panel filters only, the rubber ‘O’ ring. (The external element may be tapped lightly on the side to break it loose from the tapered seating area).
Fit new sample filter and (internal units only) rubber ‘O’ ring. Check that rubber ‘O’ ring is properly seated on the filter cap. (The external element should be tapped lightly with a smooth faced tool to reseat).
Fit sample filter cap and tighten using spanner.
Verify that there are no leaks by testing with a proprietary leak detection solution.

Record Retention

Check list for calibration of Analyzer and calibration record must be filled before & after the calibration.
Calibration checklist must be signed by concern authority and it should be filed in preventive maintenance record.
All calibration records should be kept for at least three years & after that it should be disposed off.

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