EQUIPMENT
Direct Digital Control Influence Felt Though still in infancy, technique has effect on new instrument developments appearing at ISA Show The continued infant status of direct digital control of processes has been pointed up by the Instrument Society of America's 18th Annual ISA Instrument-Automation Conference and Exhibit, held in Chicago. Some sources point out problems to be solved before direct digital control comes into widespread use. However, significant steps have been taken in valve actuators and multiplexing. Direct digital control is the application of a time-shared digital computer to control processes with many separate control loops without conversion of outputs to analog form (C&EN, April 15, page 100). To justify replacement of conventional analog controllers, the computer in a direct digital system must be able to handle many loops at low cost and high reliability. A key cost reduction is acknowledged to be the elimination of digital-toanalog conversion of outputs for valve actuation. The spotlight in this area of the show fell on Honeywell's valve division, Fort Washington, Pa. The division exhibited a digital valve positioner that it expects to sell for less than $200. Deliveries are to start after January 1964, according to the division. The digital valve positioner uses a d.c. pulse to control a pneumatic valve. Pneumatic conversion means that the unit can control a valve of almost any size in response to digital pulse commands sent to the valve site. In the Honeywell application, the unit starts to actuate a valve when the incoming digital pulse (24-volt, 0.2amp.) turns the synchronous motor. As the pulse motor revolves, it turns a screw mechanism that operates a pneumatic control. The d.c. pulse motor is a permanentmagnet motor which turns through a specified small angle when it receives a d.c. pulse. Also called a stepper motor, it is an a.c. synchronous motor that handles d.c. by means of phase switching. The d.c. pulse motor is the key in 74
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direct digital actuation. The Honeywell actuator uses a Slo-Syn synchronous motor made by Superior Electric Co., Bristol, Conn. Superior now makes Slo-Syn motors ranging from 25 to 1800 ounce-inches in torque. Honeywell uses the 25-ounce-inch motor, but designed the actuator for use of a 1-ounce-inch motor. When the smaller motor is available, lower power needs will reduce electronic costs further. The value of this motor for control is that it starts, stops, or reverses within about 1.5 cycles a.c. or one pulse d.c. A high-locking torque comes from the continuous d . c , locking the motor shaft in stopped position until a pulse arrives. Prototype. For small valves, G. W. Dahl Co., Inc., Bristol, R.I., says it is applying the Slo-Syn motors in allelectric actuators. The company says it has a prototype in which the d.c. pulse motor itself positions the valve. Dahl expects to sell production models for $183. The digital valve positioner gives incremental movement for positioning of the valve stem, with 1024 increments equal to a full stroke. Maximum speed is 400 pulses per second, or two and a half seconds for full travel. Switching operations are thus necessary before the computer signal goes to the valve. Computers give a command in something like eight microseconds. An electronic system for switching to a slower digital pulse train is an ideal place to put in proportional action. A speed range of 0 to 400 increments per second is available in the actuator. It makes the actuator move rapidly when the position error (distance from set point) is large, slowly when position error is small. Oscillators. An experimental Du Pont direct digital control system uses as the computer output a selective pulse frequency going to the Honeywell actuator. The computer, after receiving control information on a loop
through a multiplexer, switches that loop to one of 13 positions on a bank of oscillators. Six positions are positive in direction, six are negative, and one is zero. The company is now using the system on only three loops. If position error requires a large positive movement, the computer selects an oscillator with a high frequency on the positive side. Operating through flip-flop switches on the 24volt d.c. power supply for the control loops, the oscillator sets the actuator speed until the multiplexer comes back to that loop; the valve stem will move up or down at that speed. Then the computer selects another oscillator position to avoid overshooting or to stop the valve. Under development is a multiplexer that will take into consideration the needs of different loops for different time cycles. The importance of multiplexing to direct digital control can be seen in the various estimates of break-even points for number of loops controlled. Some sources indicate break-even points as low as 32 or 50 loops, others as high as 100 to 200 loops. In a technical paper at the ISA conference, L. E. Sheldon of IBM described a 300-point multirequirement modular complexer capable of terminating and multiplexing thermocouple inputs. Thus, approaches are available for large-scale multiplexing, although this one may not be directly applicable to valve actuators. Other new equipment at the ISA show points to preparation for replacement of single-loop analog controllers by multiplexed, time-shared controllers. Minnesota Mining & Mfg. Co. introduced a multiplexed, digitally operated controller capable of handling eight to 32 loops. 3M calls the unit the Digitele direct digital controller, but the unit converts output for each loop from digital to analog. Although the Digitele controller is not computer-based or direct control in the strictest sense, it indicates the trend to time-shared control.
Miniaturized Air Analyzer Measures Gaseous Pollutants 145TH
ACS
NATIONAL
MEETING
Water and Waste Chemistry A miniaturized colorimetric recording air analyzer to measure gaseous pollutants has been developed at the U.S. Public Health Service research installation in Cincinnati, Ohio. Now in an advanced prototype development stage, the instrument measures and records the color change in a metered sample after it has contacted a metered flow of air in a small absorbing column, according to Dr. Bernard E. Saltzman, Robert A. Taft Sanitary Engineering Center, and Alfred L. Mendenhall of the Occupational Health Research and Training facility. The analyzer features rapid response, minimum liquid reagent requirements, small size, and rugged all-metal construction. Dr. Saltzman expects the instrument to be used in both industrial hygiene studies inside industrial plants and air pollution studies outside the plants. Almost complete response occurs within three minutes of a change in air concentration, compared to 15 min. or more for previously available devices, according to Dr. Saltzman. The use of stainless steel tubing connections to a stainless steel block capped with glass windows adds to the ruggedness of the unit. This feature contrasts with the usual glass-tubing connections to an all-glass photometer cell which holds the reagent in conventional systems. The optical system includes a grating monochromator and an RCA 6217 panchromatic photomultiplier tube. This tube views both beams of the photometer cell. The beam from the exposed reagent side of the cell is chopped at 15 cycles per second. The square-wave signal is superimposed on the unchopped reference signal of the beam from the unexposed reagent side. The circuit, according to Dr. Saltzman, is arranged so that the photomultiplier tube dynode voltage is regulated by the reference beam to produce a constant base output voltage. The superimposed wave is rectified and feeds to a vacuum-tube voltmeter circuit which yields a 0- to 50volt signal for the recorder. Air flow through the prototype
ACF Industries Designs New In-Transit Heating Car An electrically heated tank car has been introduced by Shipper's Car Line division of ACF Industries, Inc. According to the New York, N.Y., firm, the car is capable of handling materials at temperatures above 500° F. Cars heated electrically provide safer, easier, and in many cases more economical materials handling than earlier cars that heat their contents with either live steam or natural gas, according to Henry V. Bootes, ACF vice president and division general manager. Two cars have thus far been put in service. Margarine in a liquid state is carried from a Southwest processing plant to a Pacific Northwest distribution center in one of these cars. In the other, leased to a steel producer, molten pitch is carried to aluminum manufacturers. Heat is supplied at constant temperature by a 40-kw. diesel electric generator. Diesel fuel, carried under the car, is sufficient to run the generator for about two weeks. After the engine is operating, it is completely automatic, requires no attention until the car is unloaded. The car's heating system can be from any 200-volt shop line at the unloading point.
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unit runs to about 200 ml. per minute with good absorption efficiency. At higher rates, efficiency appears to diminish, Dr. Saltzman says. While nitrogen dioxide was selected as a test gas, the equipment can be modified to measure other substances such as oxidants, nitric oxide, and sulfur dioxide in the atmosphere, Dr. Saltzman says. The rapid response of the instrument even permits measurement during brief fluctuations in gaseous pollutant levels, he adds. Furthermore, the low reagent consumption means that it can be used for long periods without replenishing the reagent supply.
Zeiss to Market Recording Spectrophotometer in U.S. Carl Zeiss, Inc., has added a recording spectrophotometer to the line of analyzers it sells in the U.S. Introduced at the ACS New York Section's Chemical Exposition U.S.A., Model RPQ 20A can be used as a double-beam instrument to measure extinction and transmittance. It has a 200-to-2500 m^. range, Zeiss says, and is adjustable to single-beam operation for flame photometry and fluorescence measurements. Reflectance measurements are made possible by a diffusion sphere attachment. The instrument will list for about $15,000, including powerpack. The reflectance attachment is tagged at $1730. Introduction in the U.S. follows the New York, N.Y., firm's development of U.S. service facilities. Zeiss emphasizes the simplicity of construction and operation of the analyzer. It has no moving optical parts and features partly transistorized amplifier circuitry. Two choppers are synchronized automatically, according to the firm. Reflectance work requires exchange of two mirrors in the measuring instrument and attachment of the diffusion sphere accessory. Measurements can be made by laboratory technicians without special training, Zeiss says. The German-made RPQ 20A brings Zeiss into competition with the Cary Model 14, manufactured by Applied Physics Corp., Monrovia, Calif. With a 185-to-2650 m/x. range, this analyzer lists for about $16,000, is designed for absorption or transmission analyses. Reflectance, fluorescence, and flame photometry attachments for Model 14 are optional. 76
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New GC Products Introduced At Chemical Exposition New products were unveiled by gas chromatograph manufacturers at the ACS New York Section's Chemical Exposition U.S.A. Some of the new products came from Wilkens Instrument and Research which introduced its Hy-FI 2 dual-channel detector system. The system, which combines both flame and electron capture detectors, is incorporated in the firm's modular gas chromatograph, Model 665, selling for $1850. With this combination, the column effluent is divided by a stream splitter to feed both detectors. The signals from both detectors are amplified by a two-channel electrometer which in turn operates a two-pen recorder. Wilkens points out that a striking trace of peppermint oil has been made with this equipment. Many peaks were picked up by electron capture which, because of their low concentration, were not detected by flame, the company adds. • Furthermore, since the electron capture detector doesn't destroy the effluent, it's possible, especially when working with perfumes and flavors, to use the nose as a detector of sorts for identification. Wilkens also unveiled its new Model 202 two-column gas chromatograph. The unit is adaptable to both dual flame and thermal conductivity detectors. Manual or linear temperature programing modules are optional. Prices range from $1480 to $1975. Perkin-Elmer displayed a new series of modular gas chromatographs. Included in the series are the base models 810 and 820, selling for about $1600 and $1495, respectively. The instruments can be adapted to use all types of detectors, P-E says.
BRIEFS New flowmeter has no moving parts in the fluid stream and may be used in either liquids or gases. Known as Model IU-62-FMP, it has been developed by International Ultrasonics, Inc., Metuchen, N.J. It consists of a thin probe extending into the flow stream and an indicator. E 30
Proportional controller is offered by Yellow Springs Instrument Co., Yellow Springs, Ohio. Designated Model
72, it has direct digital dialing of the set point which is resettable to ±0.01° C. Short-term stability of ±0.005° C. and long-term stability of ±0.01° C. are claimed by the company. The proportioning band is adjustable from 0.1° C. to 3° C. to allow optimization of the controller response to the control situation. The unit costs $345. E 31
Self-contained solid-state temperature controller is available from Research, Inc., Controls Division, Minneapolis, Minn. Named the Thermae Model TC 5192, it is designed for exacting closed-loop temperature control applications, and is capable of accuracies of 0.25%, the company says. E 32
Glass valves, engineered especially for chemical and pharmaceutical processing plants, have been introduced by Corning Glass Works, Corning, N.Y. They are armored with a coating of glass fiber reinforced epoxy resins for extra strength. All components that come into contact with the liquid being handled are corrosion resistant, Corning says. E 33
An all-aluminum cylinder has been added to Kaiser Aluminum & Chemical Corp/s line of containers for fluorocarbon. The new cylinder weighs only 30 lb., which is 46% lighter than comparable steel cylinders, according to the Oakland, Calif., company. E 3 4
New line of high-temperature, highvacuum furnaces is available from Vacuum Products Division, Varian Associates, Palo Alto, Calif. These cold-wall furnaces maintain a pressure of 5 X 10 - 9 mm. Hg at temperatures above 2000° F., according to the company. E 35
Environmental monitor for measuring and recording the alpha radiation level of airborne particulate materials is being offered by Victoreen Instrument Co., Cleveland, Ohio. Principal uses of Model VNS-4/830C will be in nuclear fuel element fabrication and processing plants. E 36
Ruby laser system is capable of firing once per minute with a power output
of at least 100 joules at 6943 A., according to its manufacturer, Maser Optics, Inc., Boston, Mass. The company adds that the system, known as Model 3100, can deliver outputs as high as 125 joules when operated under cryogenic conditions. Cost of the unit is $7200. E 37
High-temperature incinerator for destruction of liquid and semiliquid wastes is introduced by Prenco, Inc., Royal Oak, Mich. Designated Model SF-l-P, it utilizes the B.t.u. value of the waste itself to produce incineration temperatures in excess of 2200° F., according to the company. The complete unit may be easily installed as it requires only electrical plug-in and waste supply line hookup to put it into operation. It has a ca-
pacity of 3000 gal. of waste material per week, according to Prenco. E 38
Teflon-coated wire cloth for screening sticky materials is available from National-Standard Co., Niles, Mich. The coating is relatively inert, can be used at temperatures of up to 480° F., according to the manufacturer. Openings from 2 through 100 mesh are available. Applications are limited to nonabrasive materials, the company adds. E 39
Further useful information on keyed Equipment items mentioned is readily available . . .
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NEW MODEL 910 BREW VACUUM FURNACE • . . the last word in cold-wall vacuum furnaces with all the modern features you want for high performance, low maintenance. • For bright annealing, tempering, hardening, brazing, homogenizing, normalizing, degassing, sintering. • Designed to heat treat materials in vacuum or in a controlled atmosphere at temperatures up to 2400 °F. • Forced fan-cooling with built-in heat exchanger provides rapid cooling. • Heat zone heated on all six sides assures uniform work charge temperature. Usable heat zone space: 3600 cu. in. • Uniform temperature maintained by automatic controls. • Operating pressures at temperature down to 1 x 510"4 Torr. Ultimate pressure 5 x 10" Torr. • No graphite or other refractory materials used, eliminating contamination of work charge. • Fool-proof safety interlocks prevent improper operation. • Stainless steel furnace tank with low heat sink design permits rapid cooling and shorter outgassing cycle. • In addition to the Model 910, Brew's complete line consists of twenty standard models for research and general heat treating with temperatures ranging up to 3000°C and vacuums to 10"s Torr. C o m p l e t e specifications on request. See the new Model 910 at Brew Booth 1200, Metal and Materials Show, Cleveland, October.
BREW
VACUUM FURNACE DIVISION
B f t r & R D O. BREW and COMPANY. INCORPORATED
CONCORD. NEW HAMPSHIRE
SEPT.
23,
1963
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