Chapter 9 Additional facilities
Page 9.2
9.4 Fallback values and modes A fallback value is used as a temporary substitute for a parameter if a live input (i.e., the transducer, transmitter
or wiring), which is normally used to calculate the parameter, should fail.
A fallback must have one of the following modes:
•None The system uses whatever value is available for the parameter regardless
of whether or not the live input has failed.
•Last good value The system uses, for the parameter, the last value prior to failure.
•Fixed value The system uses whatever fixed value you have specified for the fallback.
You can set fallback values for:
• Line density.
• Base density.
• Line temperature.
• Line pressure.
• Specific gravity.
• Density temperature.
• Atmospheric pressure.
• CO2 and N2.
• Energy (Cv/m).
9.5 Analogue 0% and 100% values These are values which specify the zero and span of analogue inputs and outputs.
9.6 Live and set data What are live and set data?
Stored data can be either live or set. Live data is continually updated by new data received from transducers or
other transmitters. Set data is data that you have entered via the keyboard; it does not change unless you enter
new data.
Why should I want to set data?
You may want to set data for reasons such as:
•You want to test the flow computer’s programming
If you want to test the flow computer’s programming it is much easier if you use known, fixed data.
•You don’t want to monitor a particular parameter constantly or don’t want to monitor it at all.
If a parameter is not likely to change significantly or if it is not important to measure it accurately, you may
not want to connect a transducer or transmitter. In this case, set data may be accurate enough for your
purposes.
•A particular transducer or transmitter is out of action.
You can temporarily set the data to a fixed representative value until the transducer is repaired or
replaced.