Fail Safe Controller


Thread Starter


We are working in lignite based power plant.

The supplier has provided the Main Control System DCS, ABB along with FSC, Honeywell. Most of the measurement, control, monitoring, recording & trending is done by the DCS.

Tripping philosophy incorporates the software issues OFF command to MCC from DCS.Besides, "Release" hardware command through relay is issued with the help of FSC.

Thus i would like to understand:

1.Need of FSC

2.There is no field monitoring for DIs.

3.Why AI have additional termination module for FSC.

3 Why TCs are not directly connected to FSC & taken as 2-wire transmitter.

Thanks in advance.... I will come with more query

Shailesh Patel

> 1. Needs of FSC

FSC is also called as ESD (Emergency shutdown system) in big plant like Refinery. It could have lots of future which could not have in DCS. Like,

Double redundant power supply, Triple redundant IO card, Processor and internal communication Bus. Lots of free processing power (because all control action happens in DCS). Certification for mean time failure rate to calculate failure of FSC itself.

> 2. There is no field monitoring for DIs.

I don’t understand your question. If you want to say that there is no DI connected to FSC (normally it should not happen), than it depend on process of Power plant.

> 3. Why AI have additional termination module for FSC.

Do you mean that FSC have Double redundant AI module? If yes then that’s why it called FSC.

> 4 Why TCs are not directly connected to FSC & taken as 2-wire transmitter.

Normally all TCs, and RTD used with Transmitters for both DCS and FSC (ESD).

If it is not connected by transmitter then for TCs it could be voltage drop and in case of RTD there could be additional resistance due to cable.
Thanks for your reply

1))Regarding the Monitoring Ckt of DI:

If Pressure Switch is used as DI (using NO contact) while the pressure is in normal condition.

Suppose the PS wiring is loose at Field JB& thus Status at controller become NO even though the pressure crosses the limit value. i.e that there is no monitoring at field side for such cases.

Normally FSC must have provision for critical DI field monitoring resistance at PS level.The concept is known as Line monitoring described in 10106/2/1.

2)) Regarding Analog input, the additional Field Termination Module is connected named FTA-T-15 & FTA-T-14, what is the purpose& Are modules not capable to handle 2-wire transmitter directly.

Shailesh Patel

1) Regarding the monitoring Ckt of DI:
As per my opinion PS should be PSL (Pressure low), So in normal operation NO will become close (it is also depend on type of instrument). so it is possible to monitor line.

2) since I am not expert of Honeywelll FSC I can not provide answer.

Tim Niemczyk

There are modules on the market designed to be integrated into industrial control systems to eliminate false shutdowns, simplify troubleshooting, and provide early detection of faulted control wiring. Check out to see one option to help solve your particular problem.