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The system alarms are used to inform the operator of an abnormal condition. All system alarms are audible and visual. The alarms consist of hard-wired and TXP logic alarms.

6.3.4.1 Hard Wired Alarm

Hard-wired alarms comprise a high temperature alarm, a low sample flow alarm, and an analyser power fault alarm. All of these alarms are critical to the normal operation of the condensate monitoring system. Therefore, the fail-safe principle is applied to these alarms. This means that if an alarm is activated or the signal circuit to the DCS is broken (24V DC is not detected at the digital input module), an alarm is generated on

the HMI. The operator must check the instruments locally when these alarms are activated. The functions of the alarms are described as follows:

• High temperature alarm (10QUC21CT001_XB01)

This alarm is used to protect the analyser sensors from high temperature damage. A Thermal Shutoff Valve (TSV) is installed downstream of the sample cooler. The valve is normally open. However, the valve automatically shuts when the sample temperature after the cooler exceeds 49ºC. The normally closed contact in the valve breaks when the valve closes activating an alarm on the HMI.

When the alarm goes off, the operator needs check the valve locally. The valve will remain closed after it trips and can only be opened again by pushing the local reset button after the sample temperature fall below 49ºC. The function diagram for the high temperature alarm is 10QUC21CT001 in Appendix C.

• Low sample flow alarm (10QUC21CF001_XB01)

This alarm is used to detect a low sample flow at any of the analysers. The six analysers share one common alarm. If any analyser has a low sample flow, an alarm will be activated on the HMI. The operator needs to check the sample flow locally because the common alarm does not tell which analyser flow is low. The alarm can only be reset after the sample flow to all analysers exceeds the lower limit. The function diagram for the low sample flow alarm is 10QUC21CF001 in Appendix C.

• Analyser power fault alarm (10QUC21CE001_XB01)

Each analyser has an individual miniature circuit breaker (MCB) with a normally open contact. These six contacts are connected in series to share one common alarm. If any circuit breaker trips, an alarm will be activated on the HMI. The operator

6.3.4.2 Teleperm XP Logic Alarm

Teleperm XP logic alarms comprise the conditions that can negatively affect the functionality of the condensate monitoring system. These conditions are:

•Because the final determination of the contamination level relies on sodium and cation conductivity, if the two sodium signals are invalid, the function for the contamination level voting should be disabled until at least one sodium signal becomes valid.

•If both sodium signals are valid but the deviation between the two sodium signals exceeds the limit value, an abnormal condition must have occurred on at least one sodium analyser. Therefore, neither of the two signals should be used for the determination of the contamination level until the abnormal condition is cleared.

•If any two out of three cation conductivity signals are invalid, the output of the 2V3 function returns to zero therefore the cation conductivity signal should be invalid and the function for the contamination level voting should be disabled until at least two of the cation conductivity signals are valid.

The schematic diagram for the system alarms logic is shown in Figure 6.20. The meanings of each function blocks is:

• BT: Digital input signal function provided by TXP.

• &: AND Boolean function.

• ≥1: OR Boolean function.

• TD: ON delay timer. The delay time is set to 5 seconds.

• 2V3: Boolean 2-out-of-3 function. If any two inputs are TRUE, the output are TRUE.

As can be seen from Figure 6.20, if any of the following conditions in the logic are TRUE and last for at least 5 seconds, a “monitoring system fault” alarm will be generated on the HMI:

• Sample temperate high

• Sample flow low

• Analyser power fault

• Deviation of sodium signals high

• Both sodium signals invalid

• Two out of three cation conductivity signals invalid

Monitoring system fault alarm TSV shut

Na #1 flow low

pH flow low Na #2 flow low

Condy #2 flow low Condy #3 flow low

Low flow alarm

Condy #1 power fault Na #1 power fault

pH power fault Condy #2 power fault Condy #3 power fault Na #2 power fault

Analysers power fault alarm

≥1 ≥1

≥1

High temperature alarm

TD 5sec

Condy #1 flow low

BT BT BT Na #1 invalid Na #2 invalid & Condy #2 invalid Condy #3 invalid 2 V 3 ≥1 Na deviation high Hard-wired signal TXP logic Condy #1 invalid Monitoring system fault

Figure 6.20 System alarms logic schematic diagram

Diagram 10QUC26CQ901 (Page 4) in Appendix C is the system alarms function diagram. If the monitoring system is in fault, a “monitoring system fault” alarm will be

of the system. The operator must find the root cause of the alarm. Once the alarm has been cleared, all the functions will be re-enabled automatically. The five second on-delay timer makes sure that the alarm is not inadvertently triggered by a spike or noise signal.

In order to help the operator find the cause of the alarm, four alarm messages are displayed on the HMI as shown in Figure 6.21. If an alarm is activated, the associated indicator is illuminated in red, otherwise the indicator remains white. In addition, each analogue signal is displayed on the HMI. If a signal is invalid the frame of the signal display turns red, otherwise the frame remains black. For example, as can be seen from Figure 6.21, the frame of three cation conductivity signals are red, which means that all three signals are invalid. According to the logic diagram shown in Figure 6.20, if any two cation conductivity signals are invalid, the “monitoring system fault” alarm will be activated and the indicator for the monitoring system fault will be illuminated in red colour. The operator can therefore deduce that this alarm has been caused by the invalidity of the cation conductivity signals.

Figure 6.21 Alarms displayed on HMI