Control fields

Doane J W 1986 Field controlled light scattering from nematic micro droplets App/. Phys. Lett. 48 269-71... 

Presently, fieldbus controllers are single-loop controllers with 8- and 16-bit microprocessors and are options to digital field-control devices. These controllers support the basic PID control algorithm... 

The above methods provide speed variation in steps, as in squirrel cage motors or in two machines or more, as in frequency converters, and cannot be u.sed for a process line, which requires frequent precise speed controls. Until a few years ago there was no other option with all such applications and they had to be fitted with d.c. motors only. D.C. motors possess the remarkable ability of precise speed control through their separate armature and field controls. In d.c. motors the speed... 

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. 4.17 Block diagram representation of field controlled DC servo-motor.

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). 

Fixed speed. Advise synchronous speed desired (i.e., 3,600, 1,800, etc.) for AC motors. For DC motors, advise desired basic speed at full, load, and maximum speed by field control. 

Constant-speed motors are usually suited for a speed range of less than 3 to 1 by field control, but mechanical and electrical characteristics govern maximum safe speeds. With constant voltage on the armature, as the field is weakened the speed increases and the motor develops constant horsepower. 

Adjustable-speed shunt-wound motors with field control are designed for operation over speed ranges of 3 to 1 or greater. Standard adjustable-speed motors are rated in three ways tapered horsepower, continuous, 40°C rise constant horsepower, continuous, 40°C rise and constant horsepower, 1 hr,. 50°C rise, of the next larger horsepower rating than for continuous duty. 

Compound-Wound Motors. These motors are used to drive machines that require high starting torque or in which the loads have a pulsating torque. Changes in load usually produce wide speed regulation. This motor is not suited for adjustable speed by field control. 

The field laboratory set up by the field research group is a key element to completing successful worker exposure/re-entry research. The field laboratory may be set up in close proximity to the treated field, but should be located at a reasonable distance from the treated area to avoid cross-contamination of field samples and field controls. 

Field control and field-fortified urine samples were prepared with urine from individuals with no known exposure to chlorpyrifos. Some control urine samples were left unfortified (controls), and some control urine samples were spiked with a "low" amount of 3,5,6-TCP, shaken, and stored on dry ice until analysis. Some control samples were also fortified with a "high" amount of 3,5,6-TCP. 

Table 4 Field Controls and Field Spikes (Worker Exposure)...

AJ Grodzinsky, AM Weiss. Electric field control of membrane transport and separations. Separ Purif Methods 14 1-40, 1985. 

The model of electric field-controlled artificial muscles has been described in 1972 [5], Fragala et al. fabricated an electrically activated artificial muscle system which uses a weakly acidic contractile polymer gel sensitive to pH changes. The pH changes are produced through electrodialysis of a solution. The response of the muscle as a function of pH, solution concentration, compartment size, certain cations, and gel fabrication has been studied. The relative change in length was about 10%, and the tensile force was 1 g/0.0025 cm2 under an applied electric field of 1.8 V and 10 mA/cm2. It took 10 min for the gel to shrink. 

Field/Control constant communication with field no communication with field operator... 

---