Jan
02
In June, 2100 the International Electrotechnical Commission (IEC) distributed a new project proposal 65E/199/NP, Devices and integration in enterprise systems; Field Device Integration (FDI) – Part 1 to 7. Voting on this proposal was completed in October, 2011 and the new project was approved. Within IEC the SC65E WG7 committee will address converting the draft FDI …
Oct
03
The analog output block action on loss of power, that is, fail open or fail closed, is defined in Foundation Fieldbus devices through the configuration of the IO_OPTS parameter. Also, as addressed in Control Loop Foundation – Batch and Continuous Processes, this parameter is also used in DCS systems that have adopted the function blocks …
Sep
26
The process gain may be negative or positive depending on the process design. To provide the correct response a feedback control block must take into account the process gain direction—whether to increase or decrease the manipulated input to correct for a control error. For example, the inlet flow to a tank may be manipulated to …
Jan
24
One of the fundamental limitations of single-loop control is the fact that all control action is based on the error between the setpoint and the controlled parameter. If there is no error, then the control output will remain at its last value. To correct for process disturbance input using single-loop control, the disturbance input must …
Dec
13
As noted in a previous post, when work on Foundation Fieldbus specification was completed in 1994, there were very few fieldbus products on the market and even fewer control systems that supported these devices. The Fieldbus Foundation function block team discussed the need to communicate the advantages of fieldbus to inform the industry of this …
Feb
28
Many control systems have traditionally provided some capability to limit the rate of change in a setpoint value used in control. When a setpoint change exceeds this rate of change limit, then the rate limited value is use in control. Thus, the full setpoint change is not immediately seen in control until the rate limited …
Jan
26
With the introduction of digital field devices, manufactures of control systems and maintenance tools were faced with the challenge of how to access and display information in devices that were produced by different companies. Over the years, a number of approaches have been developed. However, the Electronic Device Description Language (EDDL) is the dominant technology …
Jan
22
The physical standard and technical report produced by ISA SP50 were used as a starting point for much of the work done by the Fieldbus Foundation. In particular, the Fieldbus Foundation function block specification team adopted some basic concepts such as the definition of mode and status with minor changes from the definitions contained in …
Jan
15
One of the foundation pieces of measurement and control as utilized by the process industry is the concept of mode. The mode of a measurement inputs to a control system may be used to indicate if the associated device is in or out-of-service. For a control or output function in a control system, the plant …
Dec
18
Training an operator on a new control system often includes hands on experience with a training system that supports dynamic process and control system simulation. The hardware for such a training system may be constructed using spare parts from the new control system. A simple simulation of the process can often be implemented using the …
