Should SIS input values be used in the BPCS as a deviation alarm or in a PID control loop?
This topic is related to integrated BPCS/SIS platforms where the BPCS has fast, reliable access to SIS input signal data. In cases where two transmitters are being used in the SIS for 1oo2 voting in a SIF, does it make sense to move a third transmitter from the BPCS to the SIS and then use all three signals for PID control in the BPCS? Some say that this increases the control system integrity by selecting from multiple input values, while at the same time improves SIS availability by providing 2oo3 voting instead of 1oo2. What effect does this have on the layer of protection analysis (LOPA)?”
Chuck Miller, CFSP | DeltaV SIS Business Development Manager - Americas
Emerson Process Management | 12301 Research Blvd. | Research Park Plaza, Building III | Austin | TX | 78759 | USA
O: 512.832.3436 I C: 512.466.5968
- Login or register to post comments
- 3655 reads
- Permalink
- 2 comments
SIS - Does use of HART Alerts improve process availability.
Where the SIS has direct and reliable access to HART Device Alerts should safety engineers configure these signals in the SIS to avoid nusiance trips of the process?
Chuck Miller, CFSP | DeltaV SIS Business Development Manager - Americas
Emerson Process Management | 12301 Research Blvd. | Research Park Plaza, Building III | Austin | TX | 78759 | USA
O: 512.832.3436 I C: 512.466.5968
chuck.miller@emerson.com
SIS - Does use of HART Alerts improve process availability
HART values are better suited for BPCS because of the slower rates of transmission. Safety Systems are usually configured to "act" when "this" happens. For example if a Temperature Transmitter signal to the Safety logic solver exceeds XX Degrees the logic solver needs shut down a process stream. If the temperature transmitter also sends a HART alert indicating that there may be a problem with the Thermocouple or RTD, then signal value of XX may be suspect. Not knowing whether that signal is suspect or not, we still want the logic solver to shut down the process stream. The HART alert helps in quicker trouble shooting and resolving the problem. That way the process can go back on line quicker. But the safety system needs to act regardless of whether that signal was suspect or not. So, I don't see too much value in moving the HART alerts from BPCS to SIS.