Electrical loop take-over application flow

Many distributed control systems in process plants are reaching the end of their useful lives. With today’s requirements in the field of safety, efficiency and control, a control system migration to a modern system is in many cases inevitable. To boost DCS migrations and prevent users from the production loss and downtime that usually comes with it, Istec has developed the IST-203 Hot Cutover Tool. This tool facilitates an electrical loop take-over in order to perform a DCS migration without interrupting the active production in 5 steps.

Please note that this page shows a simplified process. Please contact one of our specialists here or check the product manual for more information.

STEP 1 – CONNECT THE DEVICE

The process starts with an inventory of all processes and related instruments that will be affected by the DCS migration. Define the critical loops and perform the necessary hazard and operability studies. Connect the device to the loop in parallel with the DCS.

STEP 2 – SAMPLE MODE

When take-over is selected in the main menu of the device, it will switch to sample mode. In this stage, the Hot Cutover Tool verifies if it is connected to an active loop and receives a stable signal. If it does so, the device will show “Ready for take-over”. At this point, the Hot Cutover Tool is ready to take over the control loop from the DCS. To verify if the tool is connected to the right loop, the IST-203 comes with a check connection option. With this option, a pulse is send down from the DCS and received by the tool as verification.

STEP 3 – LOOP TAKE-OVER

When in take-over mode, the Hot Cutover Tool takes charge of the loop. Any changes made to the DCS after entering take-over mode will have no effect on the loop. At this point, the old DCS can be disconnected from the loop and the new control system can be connected. During the take-over mode, the offset control function of the hot cutover tool can be used to change the loop values if necessary.

STEP 4 – MATCH OUTPUT

To avoid any offset in the loop when ending take-over mode, the new DCS should be set to the same value as the old DCS. The new DCS output can be changed until it matches the old DCS output – the tool will absorb any offset generated. When the output matches, the device will show “Output match OK”, and take-over mode can be ended. In this stage, the Output Match function can be used to verify the new DCS output.

STAP 5 – END TAKE-OVER

When the new DCS is connected, working properly and the output matches, take-over mode can be ended. At that point, the new DCS will take control of the loop. The hot cutover tool can now be disconnected.