Variable output devices

These are mainly the feed and polymer pumps, and the decanter brake torque or speed. However, in special cases, the actual bowl speed could be a part of a control strategy. The pond depth itself, using the inflatable dam, could be used in a thickening control strategy. 

The polymer feeder could be used in a control system, if wide ranges of feed concentration were to be anticipated. As far as is known, this has not yet been used. 

Modern electronic technology has provided industry with a wide choice of small, user-friendly, cost-effective controllers, with proportional integral and derivative (PID) control action. These can be used individually on the input flows, or integrated into a master controller. It would not be unusual to have one each on the feed and polymer pumps. A signal from the flow meter would be supplied to the controller, which would adjust the speed of the pump to give a flow agreeing with the set point entered by the operator. The set point could be set alternatively by a master controller. 

The polymer control system can be augmented with a feed solids meter, to give feed-forward control, fixing the kg/t db polymer usage to an operator set point. 

The main motor controller is a separate controller, and depends upon the type of installation and motor. The motor could be AC, DC or inverter type. Rarely, it could be a hydraulic motor. The starter could be DOL (direct-online), particularly if a fluid coupling is fitted, it could be a soft-start inverter system, or a DC system. With an Inverter system the back-drive, also an inverter type, could be connected through the DC bus to allow power regeneration. The starter Itself could be actuated by a separate master system. Undoubtedly there will be interlocks with the starter, to cause it to de-energise with certain scenarios. 

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Variable output devices provide an accurate position indication of a valve or control rod. 

Quartz probes fitted with thermocouples to measure the temperature, and follow the movement of the sample. Linked transducer, i.e. a linear variable density transformer to sense the probe movement and produce a related electrical signal. Sample furnace, programmers and various output devices. 

To start the printout operation the Print... option in the Output pull-down menu is used. If there is more than one window on the screen choosing the Print... option - and using the mouse - allows you to specify the window which should be plotted. If all windows should be plotted, use the Print all option. With Printer Setup... a variety of output device specific parameters defining the resolution, the paper size and other printer variables, may be set. 

Another type of electrical pressure transducer is a variable-reluctance device. The deflections of a diaphragm of magnetic stainless steel are sensed by two inductance pickup coils. With ac-bridge circuitry, this transducer delivers a full-scale output of 40 mV per volt for a variety of ranges from 0 4 Torr (0- 0.08 PSIA) to 0- 3200 PSIA. 

A dynamic system is described by a set of state variables. We are interested to keep some controlled (output) variables as constant as possible (the regulator problem), or to make them follow some desired trajectory in time, (the servo problem). We achieve these goals by changing some manipulated (input) variables. The device for adjusting the manipulated inputs to keep the controlled outputs at their desired values (references or setpoints) is called controller. There are also external variables that are not manipulated, but may influence the process dynamics by their inherent variations. They are called disturbances. The main job of a control system is to rejecting disturbances. 

The main way of producing output is to use the print function. Print takes a list of one or more arguments separated by commas and sends them to the current output device, which by default is the computer s screen. As already shown, print can deal equally well with text, numbers, and variables ... 

Operated by a hydraulic motor, the pulling device (two opposed rolls that rotate and trap between them one or more roving, pulling them from their storage) is able to provide variable output of glass. By electronically controlling an inverter or a proportional valve it is quickly possible to vary the motor speed, providing more or less fibre in different... 

Thermodynamics has logged numerous equations of state over the years of the empirical variety. The common thread is their economy and intuition, where only a few parameters are called upon to address a constellation of forces. As the equations entail multivariable functions, they accommodate the tools of first-year calculus and, in turn, the infrastructure presented in Section 3.1. In their most basic applications, they enable conversions of independent variables into dependent ones. This is the subject of Figure 3.6. The ideal gas and van der Waals equations are represented as input-output devices. The devices accept n, T, V, measured for a gas such as argon and generate p in return. At 200 K, 0.00150 meter 2.00 moles, the van der Waals equation, with the help of Table 3.3 data, offers p = 2.07 x 10 pascals, while the ideal gas law delivers p - 2.22 x 10 pascals. The values differ because the nonideality is addressed, at least in part, by one device and not the other. The result is that the van der Waals equation better approximates the location of what will be termed the state point of the system the placement of a point in a coordinate plane such as pT. The state point placement is represented schematically in the lower half of Figure 3.6. 

Flow injection analysis is an analytical technique based on injecting a known volume of sample into carrier or reagent streams that are transported in small-diameter conduits (typically 0.5-0.8 mm internal diameter) under laminar flow conditions (Ruzicka and Hansen, 1988 Taljaard and van Staden, 1998 McKelvie, 2008 van Staden and van Staden, 2012 Worsfold et ah, 2013). In this moving stream, the sample does not decompose it is physically and chemically converted into a detectable species that causes a detector response downstream of the injection point (Ruzicka and Hansen, 1988 Taljaard and van Staden, 1998 Saurina, 2008 Saurina, 2010 van Staden and van Staden, 2012). The results will be reproducible on condition that all critical parameters (reproducible injection, controlled reaction time, and controlled dispersion) are held within certain tolerance levels (Ruzicka and Hansen, 1988 Taljaard and van Staden, 1998 van Staden and van Staden, 2012). The basic FIA instrument is composed of a multichannel pump, an injection valve, a flow-through detector, and a signal output device (originally a recorder, lately a computer) (van Staden and van Staden, 2012). Before FIA, relevant variables such as flow rates, reactor dimensions, injection volume(s) and chemical (reaction) conditions... 

In a very successful metaphoric style, all items of the computer world that have to do with programs are called software, while all the rest (electronic parts, wires, input-output devices) are called hardware. Partly countering the intrinsic semantics of these two words, in the last years software has become much more expensive than hardware. Computer elaboration is a matter of switching between electronic zero and electronic one, and therefore on the hardware side computer speed depends on the speed at which the electronic status of a solid device can be modified. This response of electrons to an electric stimulus in turn is a matter of the electronic structure of the solid (see Section 6.2). This is a technical matter. On the software side, higher speed depends on a better organization of the code. Computer speed is anyway an essential variable in the development of computational theoretical chemistry [3]. 

Figure Bl.10.2. Schematic diagram of a counting experiment. The detector intercepts signals from the source. The output of the detector is amplified by a preamplifier and then shaped and amplified friitlier by an amplifier. The discriminator has variable lower and upper level tliresholds. If a signal from the amplifier exceeds tlie lower tlireshold while remaming below the upper tlireshold, a pulse is produced that can be registered by a preprogrammed counter. The contents of the counter can be periodically transferred to an online storage device for fiirther processing and analysis. The pulse shapes produced by each of the devices are shown schematically above tlieni.

Modern control systems permit the measurement device, the control unit, and the final actuator to be physically separated by several hundred meters, if necessary. This requires the transmission of the measured variable from the measurement device to the control unit, and the transmission of the controller output from the control unit to the final ac tuator. 

NoU It is possible that at some loealioiis there is no a.e. source available, such as (or battery-operated lifts iirul motor vehicles,. Such applications may also call for a variable d.e. source. When it is so. it can be achieved with the use of a chopper circuit which uses the conventional semiconductor devices. The devices are switched at high repetitive frequencies to obtain the required variation in the output voltage as with the use of a phase-controlled lliyristor rectifier, A typical chopper circuit is shown in Ingure 6.2, i. using diodes and a controlled unidirectional semieonduetor switch, which can be a thyristor or tin IGBT. 

The performance equation of a mixer relates mixer size or mixing time to the input and output of the mixing device. The rate of transfer, r, incorporates the mass transfer coefficient, kL, and interfacial area, a, as calculated above. This rate can be used in conjunction with a material balance to relate concentrations of interest to time or size variables. 

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