CO trace Analyzer Calibration-Siemens Ultramat-6

Table of Contents

Purpose:

In this articles we will discuss about CO analyzer calibration. This article establishes the minimum guidelines to perform the calibration of Trace CO analyzer. This article also enable instrumentation guy to do primary level configuration and troubleshooting. This article is applicable for CO trace analyzer (Siemens Ultramat-6).

Definition:

Trace CO analyzer is based on Micro-mechanically manufactured Si chip whose measuring diaphragm contains thin film resistors. The resistors are regulated at a constant temperature. A current is required to achieve this, and its magnitude assumes a particular value depending on the thermal conductivity of the sample gas. This raw value is subject to further electronic processing and is used to calculate the gas concentration. To suppress ambient temperature influences, the sensor is located in a thermostatically- controlled stainless steel housing.

These are used in a process industry for continuous measurement of CO concentration. It is mandatory to calibrate them at regular intervals of time, so that there may not be any interlock failure.

Procedure’s requirement:

To perform a calibration of CO trace analyzer following precaution and things are required

Safety Precaution:

Ensure that tools necessary for performing the task are being used.
If the analyzer is a critical instrument, take necessary precautions for maintenance of critical instrument.
Wrong implementation of procedure/implementation without proper communication may lead to accidents or cause of plant trip.
Carbon Monoxide is having asphyxia property. Inhalation of carbon monoxide causes tissue hypoxia by preventing the blood from carrying sufficient oxygen. Carbon monoxide combines reversibly with hemoglobin to form carboxyhemoglobin. The reduction in oxygen-carrying capacity of the blood is proportional to the amount of carboxyhemoglobin formed. So it is recommended not to inhale the span gas while purging.

Sample requirement:

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 : min. 0 … max. 50 °C, but above the dew point

Sample gas humidity : <90% RH (relative humidity), or dependent on measuring task, noncondensing

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)

Sample Flow: (300 to 1500)ml/min

Permissible sample gas pressure With hoses:

Without pressure switch: 600 … 1 500 hPa (absolute)

With pressure switch: 700 … 1 300 hPa (absolute)

With pipes: 600 … 1 500 hPa (absolute)

(Without pressure switch):

Caution:

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

Display & Function list:

Calibration procedure:

Proper procedure is necessary to ensure the satisfactory operation.

1. Ensure the Work order is ready to perform the calibration on Analyser.
2. Ensure the work permit/Maintenance request form to perform the calibration on Analyser.
3. Put the Analyzer in CAL mode by changing the position of selector switch from Run mode to Cal mode in Analyzer panel.
4. Connect the Zero Gas cylinder (Zero GR N2) and Span gas cylinder- (8 to 10)ppm CO, Bal N2 and ensure respective sample tapings.
5. Open Zero gas cylinder and regulate the set pressure at 0.5 barg (max.) and take it inline for analyser sampling.
6. Set the flow in rotameter within the limit of (500 to 1500)ml/min.
7. Now purge the analyzer for some time until the displayed value to be stable.
8. If a considerable difference is observed in zero value then proceed with calibration. Enter in to Main Menu with help of Function key as shown in General Display above (General Display) and enter the code 222.
9. Go to Function – 22 to change the target value for Zero Calibration. Once target value is entered select Function – 20 to proceed for Zero calibration. See Function List for further help.(Function List)
10. Now press the corresponding Function key to Start Calibration.
11. Zero calibration is in progress and wait for sometime till measured value equals to target value.
12. Now Zero calibration is over.
13. Release the pressure by moving the regulator knob anticlockwise and close the zero gas cylinder using cylinder key.
14. Open the Span gas cylinder, set pressure to 0.5 barg (max.) and put span gas inline with the analyzer.
15. Set the flow in Rotameter within the limits of 500 to 1500 ml/min.
16. Purge the analyzer with same gas for some time and observe the value in the analyzer till it becomes stable.
17. If a considerable difference is observed in span value then proceeds with calibration. Enter in to Main Menu with help of Function key as shown in General Display above (6General Display) and enter the code 222.
18. Go to Function – 22 to change the target value for Span Calibration. Once target value is entered select Function – 21 to proceed for Span calibration. See Function List for further help.(Function List)
19. Now press the corresponding Function key to Start Calibration.
20. Span calibration is in progress and waits for sometime till measured value equals to target value.
21. Span calibration is over.
22. Release the line pressure by moving the regulator knob anticlockwise and close the span gas cylinder using cylinder key.
23. Now take the process sample inline to the analyzer.
24. Remove the analyzer from CAL mode
25. Hand back the work permit & Close the work.

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.

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