Actuator interface

B. E. Boser, in RE Analog-to-Digital Converters Sensor and Actuator Interfaces Low-Noise Oscillators, PLLs and Synthesizers, W.M.C. Sansen, R.J. van de Plas-sche, J.H. Huijsing (eds.), Kluwer Dordrecht, 1997. 

The DAS manual and automatic logic is independent of PMS circuitry. DAS is a standalone system that is not cormected or interlocked with PMS. Except for motor-operated valve control, no actuation interfaces are shared between the DAS and the PMS. The DAS actuation devices are isolated from the PMS actuation devices, so as to avoid adverse interactions between the two systems. The actuation devices of each system are capable of independent operation that is not affected by the operation of the other. The DAS is designed to actuate components only in a manner that initiates the safety function. This type of interface also prevents the failure of an actuation device in one system from propagating a failure into the other system. 

Woodman et al. [11] present a very similar workflow to monitor autonomous systems. They use HAZOP to identify hazards and determine (intuitively) the corresponding safety rules, which are if-then-else rules. Prom sensor observations, the monitor (safety layer) sends actuation inhibitions to both the controller and the software actuator interface. The strong point of the method is to take into account sensor uncertainty. Permissiveness is implicit. 

Block diagram of the overall SIS sensors, logic solver actuators, interfaces, displays/alarms, BPCS interfaces etc... 

According to Alami (2009), an autonomous robot is preceded by an integrated architecture that enables the robot to plan its tasks. In such way, we present a proposal for an open architecture for mobile robotic systems illustrated in Figure 4. The different blocks are implemented into both software and hardware. The architecture, from the point of view of mobile robot systems, is organized into several independent blocks, connected through a bus data, with address and dedicated control. One Master-Block controls several slave-blocks. The blocks related to the sensors and actuators interfaces, communication, and memory are under direct control of the Master-Block. 

Float-Actuated Devices Float-actuated devices are characterized by a buoyant member that floats at the interface between two fluids. Since a significant force is usually required to move the indicating mechanism, float-actuated devices are generally limited to liqiiid-gas interfaces. By properly weighting the float, they can be used to measure hquid-liquid interfaces. Float-actuated devices may be classified on the basis of the method used to couple the float motion to the indicating system as discussed below. 

Sonic Methods A fixed-point level detector based on sonic-propagation characteristics is available for detection of a liquid-vapor interface. This device uses a piezoelectric transmitter and receiver, separated by a short gap. When the gap is filled with liquid, ultrasonic energy is transmitted across the gap, and the receiver actuates a relay. With a vapor filling the gap, the transmission of ultrasonic energy is insufficient to actuate the receiver. 

Transducers The ciirrent-to-pressiire transducer (I/P transducer) is a conversion interface that accepts a standard 4-20 rnA input current from the process controller and converts it to a pneumatic output in a standard pneumatic pressure range (normally (),2-L0 bar [3-15 psig] or, less frequently, 0,4-2,0 bar [6-30 p.sig]). The output pressure generated by the transducer is connected directly to the pressure connection on a spring-opposed diaphragm actuator or to the input of a pneumatic valve positioner. 

Last but not least, designing a proper actuator can create the most headaches. We have to find an actuator that can drive the range of the manipulated variable. We also want the device to have a faster response than the process. After that, we have to find a way to interface the controller to the actuator. A lot of work is masked by the innocent-looking notation Ga. 

There are a number of vendors that sell solenoid actuated Teflon valves, which are easily interfaced to a computer. Care must be taken to chose a design where the internal volume at the valve outlet can be flushed easily between steps, however [110], Rotary selection valves have been used as well, but given the number of rotations needed for a 200 cycle deposit, various failure modes revealed themselves. 

Figure 6. Left Conventional control loops provide a localised interface between the real and the digital world. Sensors targeted at important control parameters feed information into digital control routines that can respond via actuators e.g. to maintain parameters within specified limits. Right A vital step on the route to the realisation of the concept of internet scale sensing is to adopt the principle that all analytical measurements should be capable of being internet-linked. The localised control of important parameters is maintained, but the information is shared via the internet with external users [4]. (Reprinted with permission from Anal. Chem., August 1, 2004, 75 (15), 278A-286A. Copyright 2004 American Chemical Society.)...

The central computer is called the master terminal unit, or MTU. The MTU has two main functions to periodically obtain data from RTUs/PLCs and to control remote devices through the operator station. The operator interfaces with the MTU using software called human machine interface (HMI). The remote computer is called the program logic controller (PLC) or remote terminal unit (RTU). The RTU activates a relay (or switch) that turns mechanical equipment on and off. The RTU also collects data from sensors. Sensors perform measurement, and actuators perform control. 

When mixing two surfactants species in a SOW system, an equilibrium takes place between the oil and water phases and the interface for each species. Since the two species do not necessarily exhibit the same affinity for the interface and the oil and water bulk phases, the compositions of the surfactant mixtures at interface and in the phases might be different. For instance if a very hydrophilic species is mixed with a very lipophihc one, as often recommended in the old formulation literature, then the hydrophihc surfactant has a strong tendency to partition in water, whereas the lipophihc one would partition in the oil. In this case the surfactant mixture in water will contain a large majority of hydrophilic species, i.e., it will be very hydrophilic, whereas the oil phase will predominantly contain the hpophihc species, with the remaining adsorbing at interface. This situation in which each species actuates on its own, more or less independently of the other, has been called non-collective behavior. Since the surfactant mixture composition at interface is often the one that commands the actual property of the system, such as the interfacial tension or the stabihty of the emulsion, it is most important to know how to calculate or measure the characteristics of the mixture present at interface. Such methods will be discussed in the next section. 

Produced water flows from a nozzle in the vessel located upstream of the oil weir. An interface level controller senses height of rhe oil/water interface The controller actuates the water dump valve, allowing the correct amount of water to leave the vessel so that the oil/water interface is maintained at design height. 

One area where further development of fibre-optic transmission systems is required is in the design of suitable interfaces or converters to provide sufficient mechanical force to drive control valve actuators (Section 7.22.3)[Pg.550]

The input/output units of the programmable controller constitute the interface between the PLC and the outside world. Hence, they are provided with the necessary signal conditioning functions which enable the PLC to be connected directly to the process actuators and transducers as desired. For this purpose the... 

W. Bracke, P. Merken, R. Puers and C. Hoof, On the optimization of ultra low power front-end interfaces for capacitive sensors, Sens. Actuators A Phys., 117(2) (2005) 273-285. 

L.J. Bousse, S. Mostarshed and D. Hafeman, Combined measurement of surface potential and zeta potential at insulator/electrolyte interfaces, Sens. Actuators B Chem., 10(1) (1992) 67-71. 

Levels 4 and 5 clearly affect the process economics, as both levels are directed to optimizing the process in some manner. In contrast, levels 1, 2, and 3 would appear to have no effect on process economics. Their direct effect is indeed minimal, although indirectly they can have a major effect. Basically these levels provide the foundation for all higher levels. A process cannot be optimized until it can be operated consistently at the prescribed targets. Thus, satisfactory regulatory control must be the first goal of any automation effort. In turn, the measurements and actuators provide the process interface for regulatory control. 

Devices mounted on the control valve that interface various forms of input signals, monitor and transmit valve position, or modify valve response are valve control devices. In some applications, several auxiliary devices are used together on the same control valve. For example, mounted on the control valve, one may find a current-to-pressure transducer, a valve positioner, a volume booster relay, a solenoid valve, a trip valve, a limit switch, a process controller, and/or a stem position transmitter. Figure 8-80 shows a valve positioner mounted on tne yoke leg of a spring and diaphragm actuator. 

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