Servomotors

One of the most common devices for actuating a control system is the DC servomotor shown in Figure 4.13, and can operate under either armature or field control. 

Fig. 4.16 Steady-state relationship between T t), u t) and e t) for an armature controlled DC servomotor.

DC servo-motor. Field controlled, with transfer function as shown in Figure 4.17. It will be assumed that the field time constant LylRy is small compared with the dynamics of the machine table, and therefore can be ignored. Flence, DC servomotor gain (Nm/V). 

The speed eontrol system shown in Figure 4.40 eonsists of an amplifier, a field-eontrolled DC servomotor and a taehogenerator. The load eonsists of a mass of moment of inertia / and a fluid damper C. The system parameters are ... 

Amplifier gain K2 = 3.5 Servomotor constant = 15 Nm/A Field resistance = 20H Gear ratio = 5... 

Any electromechanical device that utilizes an automated feedback servomotor to regulate the addition of titrant (a standardized solution of acid or base within a syringe) into a reaction vessel or sample to maintain pH. The rate at which the syringe expels its contents allows one to determine the rate of a chemical reaction producing or consuming protons. There are many such enzyme-catalyzed reactions whose kinetics can be examined with a pH Stat. For maximal sensitivity, one must use weakly buffered solutions. In his classical kinetic investigation of DNA bond scission by DNase, Thomas measured the rate of base addition in a pH Stat. The number of bonds cleaved was linear with time, and this was indicative of random scission. 

The differential amplifier compares the attenuated input signal from the detector-amplifier network with the reference voltage, Vq, as illustrated in Figure 6.31. The resulting error signal, V- - Vq, is amp]ified and applied to the servomotor, causing it to move in one direction if the error voltage is positive. 

Contractile properties in rodents can be measured either in vitro in a dissected muscle or in vivo in an intact preparation with an anesthetized animal (e.g., (19-20)). Measurements made under isometric conditions are perhaps most common and use the most straightforward setup. The addition of servomotors for dynamic control of muscle length allows simulation of dynamic conditions (eccentric, isotonic, etc.) that may be modified by disease or other processes (22, 23). For in vitro studies, the muscle is anchored by ligating the tendon (origin) to a support, for in vivo studies, the bone (femur) is clamped to prevent movement. The other tendon (insertion) is then coupled to a force transducer. In both cases, a recording electrode is also placed in contact with the muscle to record the compound action potential, and a stimulating electrode is used to stimulate the nerve or the muscle, as described below. 

The positional algorithm is preferred when the measurement is noisy, because it works with the error and not the rate of error change when calculating its proportional correction. Velocity algorithms have the advantages of providing bumpless transfer and less reset windup (0 or 100%), and are better suited for controlling servomotor-driven devices. Their main limitations include noise sensitivity, likelihood to oscillate, and lack of an internal reference. 

Fuel flow control in low-temperature cells is relatively simple. The control valves used are servomotor-driven quarter-turn valves, and the flow sensors can be the types used on gas furnaces, such as thermal dispersion type mass flow meters. 

In high-temperature cells, special valve designs are required to handle the fuel gas, which is up to 1000°C. These valves are used to balance the gas flows between stacks and for stack isolation to permit continued operation when some of the stacks fail. High-temperature servomotor drives (Mitsubishi and Hitachi) can be used on these valves. 

If motors are operated on a frequency converter, they can be run at higher frequencies. A typical value in servomotor technology is 87 Hz. At this value, the following speeds are obtained ... 

Lest you think that the laboratory balance has been made perfect by the servomotor, realize that the servomotor is electronic and therefore is susceptible to various types of interference. Sources of interference include ... 

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