Control circuit

The magnetic regulators allow to synthesize in one module of the X-ray apparatus main cir-euit commutator, form converter, noncontact smooth ac voltage amplitude regulator, para-metrie stabilizer, ac supply filter, fimetional protection against the short-circuit in the X-ray tube and protection against emergencies in the control circuits. 

A CIP system includes pipelines, interconnected with valves to direct fluid to appropriate locations, and the control circuit, which consists of interlines to control the valves that direct the cleaning solutions and water through the lines, and air lines which control and move the valves. A programmer controls the timing and the air flow to the valves on a set schedule. The 3A Standards for CIP components, equipment, and installation have been developed. A simple CIP system circuit is shown in Figure 11. 

Fig. 13. Cascade control schemes, where TC = temperature controller FC = fuel gas flow controller and LC = liquid level controller, (a) Simple circuit having no cascade control (b) the same circuit employing cascade control and (c) and (d) Hquid level control circuits with and without cascade control,...

For power and control circuit diagrams refer to Figure 4.1(b). 

In a V/f control generally, only the frequency is varied to obtain the required speed control. Based on this frequency, the switching logistics of the inverter control circuit control the inverter s output voltage using the PWM technique to maintain the same ratio of V/f. A W/control is, however, not suitable at lower speeds. Their application is limited to fan, pump and compressor-type loads only, where speed regulation need not be accurate, and their low-spccd performance or transient response is not critical and they are also not required to operate at very low speeds. They arc primarily used for soft starts and to conserve energy... 

A simple block diagram as shown in Figure 6.13 illustrates the operation of a DTC drive. It contains two basic sections, one a torque control loop and the other a speed control loop. The main functions of these two control circuits are as follows ... 

Tacho generator (TG) - This is an analogue voltage feedback device and can provide a speed input to the inverter control circuit. It provides only a low level of speed regulation, typically x 0.4% of the set speed. 

They arc fabricated of two power tran.si.stor.s and arc used as a single transistor and are suitable only for control circuits. They arc used to reduce the control cuiTcnt requirement and hence cause lesser heat dissipation, particularly during switching operations. 

It has a disadvantage in that it may have a sluggish response to the control circuit demands due to its high time constant (r= L/R)... 

Any of the above reasons tnay result in noise and an increase in temperature and must be corrected. Critical installations such as a refinery, a petrochemical plant, a chemical plant or a petroleum pipeline may require special precautions and control to avert any excessive heating of the bearings, which may become fire hazards. For these installations, bearing temperature detectors with a relay and alarm facility may also be installed in the control circuit of the switching device to give warning or trip the motor if the temperature of the bearing exceeds the preset safe value. 

To warn of an unfavourable operating condition by the use of an audio-visual alarm or trip or both, schemes can be introduced in the control circuit by means of a temperature detector or other devices to monitor any or all of the following internal conditions of a motor ... 

The two comparatively new type of breakers, vacuum and SFg are exceptions and have gained favour in view of their reliability and durability. For details on these breakers, see Sections 19.5.5 and 19.5.6, which also deal with their switching behaviour and phenomenon of arc reignition. Figures 12.44 and 12.45 illustrate typical power and control circuit diagrams respectively, for a 6.6 kV breaker-operated motor starter. 

Control circuit devices and switching elements - electromechanical control circuit devices 13947-5-1/1993 BS EN 60947-5-l/19 ... 

Test This is the position of the trolley when the power contacts are isolated but the control circuit is still connected, because it is tapped directly from Ihe auxiliary bus. This condition is essential to facilitate testing of control circuits with functional interlocks, without energizing the connected lotid. Isolation This is the position of the trolley when the power and the control circuits are both isolated. Depending upon the site requirements, sometimes the control circuit may be required to be still energized for some test requirements. 

All the control circuits are based on conventional electrical and electromagnetic (auxiliary contactors and timers) controls. The latest trend for large or complicated controls, however, is to have more compact, accurate... 

Keep the control circuits energized if possible, to further save on calculations and to obtain more accurate results. In the sample calculations as shown in Table I4.4 we consider this in a de-energized condition for the sake of more clarity. 

Refer to the control circuit diagram of Figure 15.24, drawn for the scheme in Figure 15.22. It is drawn on a single-phase basis for ease of illustration, where... 

Figure 15.24 Equivalent control circuit diagram for a differential ground fault protection scheme of Figure 15.22...

The time of switching between each relay step is, however, quite short, of the order of 3-5 seconds. It includes the timings of the control circuit auxiliary relays (contactors). It may be noted that of ibis, the operating time of the static relay is scarcely of the order of three to five cycles. 

In such conditions, it is recommended that the T-R be equipped with an electrical control circuit, which primarily keeps the potential constant, and, in exceptional circumstances, also the protection current. These pieces of equipment are potentiostats (for controlling potential) and galvanostats (for controlling current) [8]. 

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