Foxboro Company

IAvailable from Analabs, The Foxboro Company, 80 Republic Drive, North Haven, CT 60473. 4JL. MarvjUet and J. Tranchant, in R. P. W. Scott, Ed., Gas Chromatography, i960 (London But-terworth, i960), p. 321. 

Product brochure. The Foxboro Company EMV, East Bridgewater, MA. 

Figure 24.1. Illustrative relationship between range, span, elevated-zero and suppressed-zero. Courtesy of the Foxboro Company.

Figure 24.2. Reagent addition system. The ratio controller compares reagent flow to sample flow and maintains a preset ratio by operating control valve V on the reagent stream. The streams are then mixed in or before) the measurement chamber where the desired analytical measure ment is performed. Courtesy of the Foxboro Company.

Figure 24.3. Feedback and feedforward control systems. In feedback control, a measuring instrument obtains information at the output of a process, the signal obtained is compared to a set point, and the difference (or result) is applied to a final actuator. The result is ultimately detected by the measuring instrument and closed-loop control results. In feedforward control a measuring instrument obtains information at the input of a process, the signal obtained is again compared to a set point, but now the result is applied to an actuator that controls another input to the process. The result is not detected by the measuring instrument and open-loop control results. Courtesy of the Foxboro Company.

Figure 24.5. Proportional control action. After a load upset, the controlled variable deviates from the set point. The new control-point may then differ from the set point by the offset. Courtesy of the Foxboro Company.

Figure 24.6. The proportional-plus-integral controller. Integral action is accomplished by the series capacitor C in the feedback loop. The presence of offset causes this capacitor to charge at a rate that depends on RtC, where R, is the reset resistor. This forces the output to change in such a manner as to drive the offset to zero at a rate determined by the adjustment of the reset resistor. Courtesy of the Foxboro Company.

Figure 24.7. The proportional-plus-derivative controller. Derivative action is accomplished by a shunt capacitor C across Rf. When deviation from the setpoint is rapid, the low reactance of the capacitor causes less negative feedback—hence, greater amplifier gain. The derivative time resistor Ra allows adjustment of the magnitude of derivative control action to a given rate of change of the error signal. Courtesy of the Foxboro Company.

Figure 24.9. Output response behavior of discrete instruments, t, — sampling dead-time = t2 — h = ti — ts = ta = analytical deadtime = h — tz = h — ti = ts + ta < ta < It, + 2ta, where ta is the total measurement dead-time. Courtesy of the Foxboro Company.

Figure 24.10. Ute sampling controller. The sampling controller accepts a logic signal from a discrete analyzer the chromatograph) and applies corrective action for a control interval established by a timer. Courtesy of the Foxboro Company.

In 1931, the Foxboro company announced its Stabilog controller which had a wide... 

Figure 4. External view of a typical controller used from around 1925 onwards (from Foxboro Company catalogue).

Figure 7. Diagram illustrating the principle of the Foxboro company pneumatic controller (Foxboro Company Bulletin 177-1, circa 1925)...

Figure 10 Digital electrodeless conductivity instrument used for online process measurements. (Courtesy of The Foxboro Company, Foxborough, USA.)...

The Wilks Mini-Cell liquid sample holder is available from the Foxboro Company, 151 Woodward Avenue, South Norwalk, CT 06856. We recommend the AgCI cell windows with 0.10-mm depression rather than the 0.025-mm depression. 

The Foxboro Company, Corporate Research Center (N01-2A), Foxboro, MA 02035... 

Clarkson University, 339 Czechoslovak Academy of Sciences, 370 Dow Chemical Company, 478 Electrofuel Manufacturing Company, 543 Foxboro Company, 429 Greater Manchester Museum of Science and Industry, 50... 

Control Mode Adjustments," The Foxboro Company, Janu- ... 

The Foxboro Company Differential Vapor Pressure Cell Transmitter, Type 13VA, Technical Information Sheet 37-91a. 

The Foxboro Company, Turbo Compressor Anti-Surge Control, Application Engineering Data 000-25, June, 1965. 

The Foxboro Company Fractionating Column Heat Input Control by Pressure Drop Method, Application Eng. Data 282-14. 

The Foxboro Company, Foxhoro Dew Point Recording System, Using the Dewcel Element, Technical Information Sheet 19-30a. 

Fleming Instruments Ltd, Caxton Way, Stevenage, Hots. UK Flowvision, Kelvin Microwave Cotp., Charlotte, NC, USA, (704) 357 9849 Foxboro Company,Bristol Park, Foxboro, MA 02035, USA, (617) 543 8750 Fortress Dynamics, 25 Ladysmith Road. Gloucester, GLl 5EP, UK, (01452 305057)... 

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