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02/05/2024

IFL alarm. The pressure sensor is out of calibration limits. Kongsberg Troubleshooting

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.

IFL alarm. The pressure sensor is out of calibration limits

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.

Alarm list
Alarm list

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 pressure transmitter transmits a 4 – 20 mA signal (RAI_16 module)
The pressure transmitter transmits a 4 – 20 mA signal (RAI_16 module)

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.

High temperature in the generator stator winding
High temperature in the generator stator winding

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.

Distributed Processing Units (DPU)
Distributed Processing Units (DPU)
DPU
DPU
Signal transmission diagram from sensor to DPU
Signal transmission diagram from sensor to 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.

Module RAI_16
Module RAI_16
RAI_16 work
RAI_16 work
DPU cabinet no. 3 (general view)
DPU cabinet no. 3 (general view)
Our RAI_16
Our RAI_16

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.

Engine sensor and junction box
Engine sensor and junction box
Pressure transmitter
Pressure transmitter

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.

Zero and Span on the transmitter
Zero and Span on the transmitter

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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