We are developing "SIF Response Time" calculations for an Oil and Gas application for which I am looking for some guidance on how to establish the "response time" of 3051S transmitter in terms of which all parameters / lags need to be added to it. Below I have separated my query into specific questions:
I can provide more details in response to the queries above.
Many thanks in advance for your help in this.
To respond to your above questions:
1. The safety response time for a SIF is the value that relates to overall process safety time, accounting for the final element, logic solver, and sensor response times. For a sensor (in this case, the transmitter), response time is the delay between a change in pressure on the isolator and when that change is reflected on the output. Considering this, the safety response time of the sensor and dynamic performance of the sensor are the same. The published values for dynamic performance and safety response time are different because they account for different conditions: the published dynamic performance value of 100 ms is true at 75 deg F, while the published safety response time of 1.5 seconds accounts for a “worst case” scenario (for example, at extreme ambient conditions, with certain fill fluids, etc.). The published safety response time is a very conservative number to ensure the response time of the SIF can meet the needs of the application.
Diagnostic response time (or the diagnostic test interval) is separate from safety response time (or the dynamic performance of the sensor). Safety response time is the response time for the process, while diagnostic response time is the response time for transmitter self-checks. So, if a problem is detected in the process input, the next process reading output will be to an alarm state. If a problem is detected in the transmitter itself, the output will alarm on the next diagnostic update.
2. The Advanced Diagnostics suite is an optional feature available on the 3051S, and these diagnostics monitor for issues external to the transmitter. The main diagnostics contained in this package are:
- Loop Integrity – to detect issues in the entire electrical loop, from the transmitter to the host
- Plugged Impulse Line – to detect blockages in impulse piping that prevent the transmitter from having visibility to changes in the process
- Process Intelligence – to detect abnormal conditions in the process, such as pump cavitation or distillation column flooding
When configuring Advanced Diagnostics, the user can choose whether a diagnostic trip will drive the analog output to its alarm state or simply generate a HART alert. Certain self-diagnostic capabilities come standard on all transmitters and will always drive to an alarm state when tripped, such as if a sensor module failure is detected.
3. The published 1.5 second safety response time is the “worst case” time delay for the entire 3051S series of transmitters, but note that this value applies to the transmitters only. It does not account for additions to the transmitter such as seals, capillary, or flow elements that may increase response time. Response times for these more complex sensor assemblies can be calculated using a tool like Instrument Toolkit, which can be downloaded here.
4. The safety response time already includes the update rate.
5. Damping changes the response time of the transmitter by smoothing the output if there are rapid input changes. Therefore, damping will impact the safety response time because it will take more time for a change in the input to be reflected in the output.
I hope this is helpful. Please feel free to reach out here with additional questions, or email me at firstname.lastname@example.org.
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