Drive System and Controls

Key Questions What tasks are carried out by the drive system and 

Which major modules do these systems consist of  

The Plasticating and Injection Unit (Lesson 3) The Clamping Unit (Lesson 5) 

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Specifications for equipment have also in the past been very detailed, primarily to avoid the problems that would occur if bidders intended to use cement grout pumps for chemical grouting. Most often, the described details cover a page or more, with separate paragraphs dealing with capacity (pressure and volume), materials of construction, number of pumps, drive systems, and control systems including gel time control, pressure and volume control, and systems to prevent overpressuring or inadvertent... 

Testing the fuel handling system and control rod drive mechanism in air at room temperature prior to sodium charging. 

Sometimes the frame is mounted on a sub-frame together with the drive motor, and where necessary a back-drive system, to control the gearbox pinion shaft, which will in turn control the conveyor-to-bowl differential speed. The back-drive system will be described later, but for the present it suffices to say that it is essentially a braking motor or similar device coupled to the gearbox pinion shaft. The main motor is offset from the bowl and drives the bowl by means of a set of V-belts. The back-drive can also be offset, in which case it would be connected with a timing belt. The timing belt is to facilitate more accurate speed control. However the back-drive system can also be mounted direct in line with the pinion of the gearbox. 

The control of the main drive is relatively simple and straightforward. The control of the back-drive system has required dedicated development. Today the back-drive systems can control the decanter at a fixed differential, at a fixed torque or cake dryness or with some hybrid control system. The hybrid system, say, controls at a fixed differential, until a pre-set torque limit is reached and then at that torque level until the differential changes to a pre-set level. 

With main drive and back-drive systems under control, it remains to control centrate quality. For this, a good centrate monitor is required, capable of assessing the level of suspended solids in the centrate. This has been difficult but there are a few reliable devices now available on the market [20]. The monitor is then coupled via a PID controller to the polymer pump speed control. 

The electrical and electronic control system consists of the field devices feedback system, electric motor drive system and the safety and manual logic system. The commands from the micros ar checked in the safety logic system for safe operation before being sent to the fluid power system. The fluid power system operates the device in the correct direction, at the required speed and force, to position it accurately. The feedback device (say potentiometer) is read by the micro and appropriate commands initiated. The device is also connected to the computer independent display on the console. Operation and alarm messages are diplayed on the VDU and logged by the printer. 

Continuing NRC review of this event identified a potential for unacceptable interaction between the control rod drive system and the nonessential control air system therefore, IE Bulletin 80-17 Supplement 3 was issued on August 22, 1980. This Supplement required affected BWR licensees to implement operating procedures within five days, which required an immediate manual scram on low control air pressure, or in the event of multiple rod drift-in... 

It consists of a stepper motor drive system and a valve coupled with stepper motor. The drive system accepts 4-20 mA current signal from the controller and generates proper sequence of position signals proportional to the modulus of the deviation of the control signal from 12 mA. The stepper motor operated valve has been used successfully for primary and secondary air control in a sulphur furnace, condensates control in desuperheater, SO2 control in sulphiter, imbibition water temperature control etc. 

One successful total artificial heart is ABIOMED s electric TAH. This artificial heart consists of two seamless blood pumps which assume the roles of the natural heart s two ventricles (Fig. 7). The pumps and valves are fabricated from a polyurethane, Angioflex. Small enough to fit the majority of the adult population, the heart s principal components are implanted in the cavity left by the removal of the diseased natural heart. A modest sized battery pack carried by the patient suppHes power to the drive system. Miniaturized electronics control the artificial heart which mns as smoothly and quietly as the natural heart. Once implanted, the total artificial heart performs the critical function of pumping blood to the entire body (6). 

The steam balance in the plant shown in Figure 2 enables all pumps and blowers to be turbine-driven by high pressure steam from the boiler. The low pressure exhaust system is used in the reboiler of the recovery system and the condensate returns to the boiler. Although there is generally some excess power capacity in the high pressure steam for driving other equipment, eg, compressors in the carbon dioxide Hquefaction plant, all the steam produced by the boiler is condensed in the recovery system. This provides a weU-balanced plant ia which few external utiUties are required and combustion conditions can be controlled to maintain efficient operation. 

V ri ble Frecjuency Drives. An important energy by-product of soHd-state electronics is the relatively low cost variable speed drive. These electronic devices adjust the frequency of current to control motor speed such that a pump can be controlled direcdy to deUver the right flow without the need for a control valve and its inherent pressure drop. Eigure 11 shows that at rated load the variable speed drive uses only about 70% as much power as a standard throttle control valve system, and at half load, it uses only about 25% as much power. 

With the advent of the microprocessor, digital technology began to be used for data collection, feedback control, and aU other information processing requirements in production facUities. Such systems must acquire data from a variety of measurement devices, and control systems must drive final actuators. 

An interlock is a protec tive response initiated on the detection of a process hazard. The interlock system consists of the measurement devices, logic solvers, and final control elements that recognize the hazard and initiate an appropriate response. Most interlocks consist of one or more logic conditions that detect out-of-hmit process conditions and respond by driving the final control elements to the safe states. For example, one must specify that a valve fails open or fails closed. 

Although motors and controllers can be bought separately, the trend is to purchase a system from a given manufacturer. There are six types oi variable-speed drives, as own in F ig. 29-73. Dynamic response indicates the ability of the drive to respond to a change in command it is measured in radians/second the higher the number, the faster the drive response. 

But where accurate speed control is the process requirement, static controllers, termed slip recovery systems (Section 6.16.3) are recommended, which in addition to exercising extremely accurate speed control, also conserve slip losses. Static drives are discussed in Chapter 6. Below we will describe a procedure to determine the value of resistance, its steps and switching and control schemes for these steps for a rotor resistance starter. 

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