Overload protection

In other designs, a diffused siUcon sensor is mounted in a meter body that is designed to permit caUbration, convenient installation in pressure systems and electrical circuits, protection against overload, protection from weather, isolation from corrosive or conductive process fluids, and in some cases to meet standards requirements, eg, of Factory Mutual. A typical process pressure meter body is shown in Figure 10. Pressure measurement from 0—746 Pa (0—3 in. H2O) to 0—69 MPa (0—10,000 psi) is available for process temperatures in the range —40 to 125°C. Differential pressure- and absolute pressure-measuring meter bodies are also available. As transmitters, the output of these devices is typically 4—20 m A dc with 25-V-dc supply voltage. 

Manual and Magnetic Starters Manual motor starters are operated by hand. The simplest type of manual starter is a snap switch with no overload protection, used only for motors of 1,492 kW (2 hp) and smaller, usually single-phase motors with integral overload protection. 

Overload Protection Overload relays lor protecting motor insulation against excessive temperature are located either in the motor control or in the motor itsell. The most common method is to use thermal overciirrent relays in the starter. These relays have heating characteristics similar to those ol the motor which they are intended to protect. Either motor current or a current proportional to motorline current passes through the relays so that relay heating is comparable to motor heating. 

Some overload-protection schemes measure motor-winding temperature directly various methods are used. Small single-phase motors are available with built-in overload protection, A thermostat built into the motor senses motor-winding temperature directly. 

Nole.s I) For a eloser overload protection, more eurves should be drawn for r/r > (2) These points are not relevant for ///r < 200%. 

For overloading during normal operation, which may be due to load fluctuations or failure of a few capacitor elements, normal overload protection will suffice, as discussed for shunt capacitors (Section 26.1.1(3)). This protection may be provided in conjunction with the line fault protection scheme, discussed below. 

Current mode control has an inherent overcurrent protection. The highspeed current comparator provides pulse-to-pulse current limiting. This form of protection is a constant power form of overload protection (see Section 3.11). This form of protection folds back the current and voltage to maintain a constant power into the load. This may not be optimum for all products, especially where the typical failures slowly increase the failure current. Another form of overload protection can also be placed in the circuit. 

In order to overcome (1) it is often necessary to introduce a form of assisted starting, which can also help in overcoming problem (2). However, modification of the overload protection device characteristics may also be necessary. 

You could eliminate the inter-cylinder feed on a 4-cylinder engine by using four separate small inverters instead of one larger one. The small ones are fairly cheap and many have overload-protection circuitry so no fuse is needed in the battery lead - those that don t will have their own fuse. With this system, each inverter feeds just one... 

Sealing station overload protection Cooling station... 

Preventing the overloading of processing equipment, such as grinders and conveyors. Consider installing overload protection devices on drive motors. 

The only reliable means to overcome these problems in punch-and-die presses is to employ hydraulic actuation of the punch(es) (Fig. 8.95b). The timing of the punch strokes as well as the rate of increasing or decreasing pressure and the dwell time can be easily adjusted. In addition, hydraulic presses typically feature overload protection by gas filled accumulators and, because there is no physical limit to the length of the stroke, densification ratios can be very high, thus allowing successful compaction of large amounts of feed even if its initial bulk density is low. 

Pressurizing Design None Fixed rollers No overload protection Shear pin or similar... 

Roller presses that are used for the compaction offertilizers (Fig. 6.6-16) feature selfaligning roller bearings, optimally sized steel bearing blocks, and a hydraulic pressurizing system with proprietary functions and hydraulic accumulators. The latter allow adjustment of the pressure-response characteristic and provide for overload protection. While in some cases simple gravity feeders with flow control baffles are provided, most applications require one or more screw feeder(s) with variable (e.g., hydraulic) speed drives to force the material to be compacted into the nip between the rollers [B.48, B.97]. 

As shown in Fig. 6.2-40b, another but more technically detailed evoluted presentation of a typical high speed, high-pressure rotary tabletting machine, quite often, the maximum pressure is produced by one (or two) set(s) of press rollers that oppose each other. One or both are supported by springs to provide overload protection. In such machines, the final compaction takes place very quickly and is followed by a sudden... 

Distribution systems—feeders, unit substations, transformers, switchgear, and overload protection... 

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