ONGC_GCS_Ramnad

If RTD connection with TT breaks down, the serial communication between FC-101 and UFM is also breaking down.

MANOJ CHERUKAT ‎ ‎ 159 Views

Issue: If RTD connection with TT breaks down, the serial communication between FC-101 and UFM is also breaking down.

Background: The Pressure transmitter PT & Temperature transmitter TT are connected using HART links to Flow Computer FC-101 and RTD is connected by means of three wire to TT. The Flow computer reads flow values from the ultrasonic Flow meter (UFM) using the RS485 MODBUS link. It also writes the line pressure and temperature values from its registers to the UFM registers. This is required to carry out meter body corrections by calculating young’s modulus and to correct the flow by UFM.

Reason: When the RTD is disconnected from TT, the temperature value calculated by TT is a huge value (what is displayed on FC is of order 10⁸degrees C.) This huge value when written to UFM causes some kind of overflow and the communication between FC & UFM is dropped with error “SICK LINK”, RX fail.

Therefore, if there is any loose contact in RTD terminals, the flow can keep going to zero intermittently with same SICK link alarms and in normal course, the focus would be on flow computer and UFM for such link issues and this RTD angle may not be looked into.

So spare a thought for this issue if any troubleshooting is required in future.

DCS

MANOJ CHERUKAT ‎ ‎ 209 Views

1. INTRODUCTION

Ramnad Plant has a Distributed Control System or a DCS to control, monitor and store the process history. The basic details are given in this file Green:- Power LED, should be on in active card and flashing in standby card

Red :- Error LED, should be off obviously

Yellow one each for Ports 1 & 2:- off:- Port disabled

Flashing:- No configuration/port communicating, but faulty fieldbus device

The FF powersupply also has red error LED for module failure.
The diagnostic module has 4 amber LEDs to indicate the status of 4 Field Barriers.

5.2 FF communication basics

H1 fieldbus technology is modelled on OSI and has Physical layer, Communication layer and Application layer. 16 FF devices are supported on each segment.
The communication layer is made of Data Link layer, Fieldbus Access Sublayer and Fieldbus Message specification. Data Link layer controls the transmission of messages on fieldbus segment

The H1 card functions as the Link Active Schduler (LAS) in communication layer. Some of its functions are:-

(1) Scheduled transfers (2) Unscheduled transfers (3) Maintaining Live list

(1) Scheduled Transfer
Compel Data Schedule in Scheduled transfers
Scheduled transfers are regular in nature and LAS maintains a schedule of devices called COMPEL DATA SCHEDULE . Each device has its buffer and compel messages go out from the LAS to each device cyclically. The device responds from its buffer. The devices which are configured to receive the response are called subscribers.

VIRTUAL COMMUNICATION RELATIONSHIP (VCR)

link between parameter from one device to parameter of another device on the segment is called VCR. some devices support publisher and subscriber VCRs whereas some support Free VCRs

link from function block of controller to function block of device- publisher VCR

link from function block of device to controller- subscriber VCR

link from function block of device to function block of device- subscriber VCR

output link-> publisher, input link-> subscriber

Device limits

H1 card supports 35 publisher (o/p) VCR and 50 subscriber (i/p) VCR per port and total number of VCR should not exceed 50. If a Backup link scheduler is provisioned in the link, it should be able to provision for required VCRs else backup link master will not work.

Some devices have Free VCRs, these VCRs can function as publisher, subscriber or device alarm.

(2) Unscheduled Transfer
User initiated changes such as setpoint changes, tuning changes and downloads are carried out as LAS gives all devices a chance to send unscheduled messages between transmission of scheduled messages by way of issuing a Pass Token (PT) <which circulates in the segment>.The LAS maintains a list of devices , this list is called LIVE LIST. when device receives a PT, it sends unscheduled messages until it has finished or token hold time timeout is reached.

(3) Maintaining LIVE LIST.
A device can be added anytime to the segment. Between the times, it sends compel messages, The LAS sends PROBE NODE (PN) messages to devices not in the live list. The device responds with a PROBE RESPONSE (PR) message and gets added to LIVE LIST.

5.3 REPLACING A FF TRANSMITER
1. In delta V explorer, browse the FF I/O card and rt click the particular device and click on decommission. The device appears in the decommissioned nodes. Rt click and click standby to change the state.
2. Delete the placeholder for the device.(say the tag name was FT-4001)
3. Connect the new transmitter in the field. It appears in the decommissioned devices
4. Create a new placeholder with same Tag name FT-4001
5. Drag n drop from the decommissioned device to this placeholder
6. If DD (Device Descriptor) files are existing for this transmitter, follow the wizard steps to commission the device. Else, download the DD files from Emerson website and add it to the Library. One of the files should have a .fhx extension , else it will not be loaded in Delta V environment. Download the file for the correct version of device, delta v and AMS. The delta v download site is user friendly and can search for all these parameters easily.
7. Repeat step6 and complete the wizard. Download the newly created placeholder FT-4001
8. In the controller node, check the modules which use this AI, rt click and assign AI to the newly created FT-4001 to these modules.
9. Download the Modules
10. Open the AMS device manager and perform the necessary re-ranging of transmitter.

6. References

1. Getting started with your Delta V Digital Automation System. download here