Today we got an alarm G/E 2 H.T. C.F.W in press IFL on fresh cooling water pressure on auxiliary engine No.2 (which was not in work). In this article, I propose to figure out what kind of alarm this is and how to fix the problem.
First of all, let's turn to the instructions to understand what IFL alarm is. According to the instructions, IFL alarm is an alarm based on a low value of the input signal; if the pressure transmitter transmits a signal below 4 mA, then this alarm appears.
If it gives above 20mA, then the IFH signal is output. In simple words, the transmitter went out of calibration limits (below 4mA) and the first photo shows that the pressure reading corresponded to -0.33 kg/cm2 instead of 0 kg/cm2.
IFL - Instrument failure low alarm. Used for example when a 4 to 20 mA current loop is giving less than 4 mA.
But many other modules are involved in the signal transmission circuit from the transmitter to the alarm monitoring system, so it is too early to make a conclusion about a sensor malfunction.
The first thing you can check in this situation is the DPU unit, which processes and amplifies the signal from the transmitter to the host computer. DPU unit is a monitor for processing and transmitting analog and digital signals from various sensors of an alarm monitoring system.
This ship (I mean the vessel I'm on now) often has similar malfunctions and they are associated primarily with increased vibration and it is enough to tighten the required contact in the DPU unit.
For example, recently there was a high temperature in one phase of the generator stator winding. As a result, a poorly tightened contact was found in the DPU.
In DPU cabinet No. 3 we find our module RAI_16 and tighten the corresponding contacts of the pressure transmitter.
DPU - Distributed Processing Unit. Main functions are to monitor analogue or digital sensors and to provide analogue and digital output to different devices.
RAI - Remote Analogue Input. This unit has 16 analogue input channels. Each channel is selectable as voltage, current and resistance input in different ranges and has free technical units scaling. It also incorporates a 5 to 500 Hz counter channel.
Tightening did not give a successful result, so we turn directly to the sensor itself and the junction box.
The contacts in the junction box were tightened and checked, which also did not lead to a positive result. All that remains is the transmitter itself.
Each pressure transmitter usually has the ability to be calibrated using dedicated Zero and Span potentiometers that correspond to zero and maximum pressure values (4-20 mA).
In our case, we use the Zero potentiometer and bring the pressure value on the monitoring system to zero (by turning the potentiometer clockwise). This operation was done with the help of two people and next to the monitoring system, so no additional devices were used.
Multimeter in ammeter (mA) mode
In another situation, if this is not possible (by influencing the potentimeter to visually change the parameter on the host computer), it is necessary to use a multimeter in ammeter (mA) mode, connecting it in series to the open circuit of the sensor. In this case, you need to bring the output current value to 4mA.
Thus, through calibration, we brought the cooling fresh water pressure value to zero when the auxiliary engine was not in work.
If the above steps do not help, then you need to replace the damaged pressure sensor with a new one. This may require additional calibration.
In the article, I specifically examined the entire signal transmission circuit from the transmitter to the alarm monitoring system in order to clearly show the weak sections of the entire circuit. Usually in such situation it is necessary to immediately check the pressure sensor, check its contacts and perform calibration.
System model: Alarm monitoring & control system Kongsberg K-Chief 500
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