Monitoring the status of the protocol elements

Monitoring the status of the different protocol elements (PREs) in our SICAM RTU based SCADA system is not only a safety-critical requirement, but can be of great help in locating sporadic communication problems. The SICAM TOOLBOX II with its great flexibility offers us many configuration options, so we can freely decide how detailed the communication should be monitored.

In this article I will discuss two major cases:

1. Monitoring each PRE separately, to detect if a communication problem has occurred
2. Monitoring each device one by one on each PRE separately

Both cases will be discussed based on the following example: let’s suppose we use a SICAM AK3 as a data concentrator in a MV/LV transformer substation. The AK3 communicates on C2-PRE2 with the medium voltage bay controllers and on C2-PRE3 with the low voltage bay controllers. Basically the AK3 is used for protocol conversion, 103 to 104 on medium voltage side, and Modbus to 104 on low voltage side. Let’s also suppose that there are 5 bay controllers both on MV and LV side, so a total of 10 devices must be monitored.

1. Monitoring each PRE separately, to detect if stations are disconnected

In case our SCADA system is very small and simple, just checking if there is a general communication error in the system could be enough, but would make localizing bugs really hard. Therefore we would like a configuration which makes us easier to detect if eventual communication problems are caused by the medium voltage bays or the low voltage bays.

For this purpose, we will have to get the error messages from the Sum diagnostics table of our SICAM AK3. We have to take care, though, that the firmware has a separate error message for communication fault (one or more devices are disconnected) and communication failure (all devices are disconnected).

One simple solution would be, that we define the two system data points for communication fault and communication failure, but usually the dispatchers do not want to be flooded with unnecessary data, so they will only want to see if there is a communication problem on the respective PRE or not. For that, we will define a third software data-point, which simply sums the two error messages using an OR gate in CAEx Plus.

OPM configuration for communication failure

OPM configuration for communication fault

Sum of the two type of communication errors

2. Monitoring each device on each PRE separately

The SICAM RTUs can be configured to deliver information about each device on each PRE separately. We just simply need to create a system image for each device. In this particular case this means 5 images for the MV bays and 5 images for the LV bays. This time, the error messages must be read from the Detailed diagnostics table.

In order to correctly configure the system images, we need to check the station definition in the System technique and the Diagnosis information of the protocol element:

The communication with the low voltage bays is done over the MODMA0 protocol element, so we need to find in the list of system elements the MODMA0. In the right side of the window all types of diagnosis information are listed. Let’s find here the information regarding the communication faults.

As we have all the infromation we need, let’s just set the parameters of the system image:

• we will be monitoring the communication over C2-PRE3, so Lk_Bse: 002 and SSE: PRE03.
• the Diagnostic class is class communication and the Diagnostic record and bit are provided by the help document of the protocol element.

Do not forget to check the correct help file when configuring the system images for the medium voltage level bays.