CO2 analyzer calibration | Servomex 4100 Series |

Table of Contents

This Article establishes the minimum guidelines for E&I Technicians or engineers to perform the calibration of CO2 analyzer. This document also enable E&I technicians to do primary level configuration and troubleshooting.

Scope and responsibility

This document is applicable for Trace CO2 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 CO2 analyzer.

Definition

Trace CO2 analyzer is based on GFx (Gas Filter correlation) Technology. These are used in a process industry for continuous measurement of CO2 concentration. It is mandatory to calibrate them at regular intervals of time, so that there may not be any interlock failure.

Low calibration gas for GFx sensor modules may be specified between (-5)vpm and (+5)vpm of the measured component. Zero grade nitrogen is recommended.

The high calibration gas can be in the range 6 to 110% of the transducer’s FSD. As GFx sensors are configured as ‘dual range’ units, it is recommended that the high calibration gas is selected at the top end of the range used.

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 GFx sensor- (500 to 2500)ml/min

Pressure driven options Nominal- 5 psig/ 35 kPa | Range- (2 psig /14 kPa to 8 psig/56 kPa)

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 8 psig 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 Weeks

Calibration Procedure

Proper procedure is necessary to ensure the satisfactory operation.

Ensure the Maximo Work order (print copy after WO released) is ready to perform the calibration on Analyser.
Ensure the work permit/Maintenance request form to perform the calibration on Analyser.
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 (Zero GR N2) and Span gas cylinder- (8 to 10)ppm CO2, Bal N2 and ensure respective sample tapings.
Open Zero gas cylinder 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 (500 to 2500)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, set pressure to 0.5 bar g and put span gas inline with the analyzer.
Set the flow in Rotameter within the limits of 100 to 250 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.

EIS Calibration Procedure

AI-1239 is considered as Element Important for Safety. As part of EIS management it is necessary to check the operational functionality of EIS periodically.

This procedure is applicable only when Plant is under shut down.

Frequency to check EIS functionality – One year

First simulate all the prerequisite for APU and then give on command for APU to start.
Connect span gas cylinder (8 PPM CO2 BAL N2) to its respective tapings.
Open the span gas cylinder, set pressure to 0.5 barg (max.) and put span gas in line to the analyzer.
Do not put analyzer in calibration mode.
Observe the CO2 concentration in the analyzer as well as DCS.
When it reaches 1PPM it generates alarm in DCS and when it crosses 3 PPM it enables interlock. There is a delay of 15 minutes for this interlock to initiate tripping of plant.
Now wait for 15 minute. After 15 minute interlock acts and it trips APU.
Now close the cylinder and normalize all the conditions which were simulated prior to start of this procedure.
Put the process sample in line to analyzer so next time when plant starts CO2 content is monitored.

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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