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Computer Monitoring of Recirculation Systems "An Alarming Thought"James
M. Ebeling Introduction"Aquaculture is agriculture", and like modern agriculture, aquaculture is progressing towards intensive, controlled environment production units (i.e. intensive recirculation systems). Through this technology comes an increase in production potential, but with a corresponding increase in risk of catastrophic loss. In pond aquaculture, response times are often measured in terms of hours and even days. In intensive systems, response time can be measured in heart beats. This leads to a need by a manager for accurate, real-time information on systems status and performance, and reliable backup for critical systems. As a preface to this discussion, even an engineer has to confess that the most sophisticated monitoring and alarm system is an attentive human operator. An experienced manager can detect the moment he or she steps into a facility whether something is amiss, often just from a change in background noise. But most facilities are not staffed continuously, or are complex and spread out over several buildings. (Based on my own experience, most system failures occur either late Sunday, or ten minutes after the last person has left the facility.) Thus, the need for some form of continuous monitoring of critical water quality parameters and of selected systems. Factors that affect the design of any monitoring/alarm systems, include: 1) type and size of facility: whether it is a hatchery, production and growout system, or just broodstock maintenance; cold water or warm water facility; freshwater or saltwater; the source of water from wells or gravity fed; single building or multiple buildings. 2) type and number of tanks: circular rearing tanks, raceways, or small ponds; individual rearing tanks or large production tanks; aeration with air or oxygen injection; recirculation or flow through systems. 3) number and value of fish: semi-intensive, intensive or super "just keep them wet " intensive systems; baitfish, trout, catfish, or prize Koi. 4) location and operating procedures: remote location or next door; on-site staff, full or part-time operators. 5) budget: just one bell or microcomputer controlled back-up response. What follows is a brief discussion of technology that is currently available for monitoring an intensive recirculation system and provide for adequate back-up in case of system failures. Various types of sensor, probes, and monitoring equipment will be described, as well as integrated systems. Both high-tech and low tech solutions will be presented. But what must be emphasized again is that the best monitoring/alarm systems is still an attentive operator and second that any system is only as good as the care that is taken in its design, installation and maintenance. MonitoringPriorities "A Question of Timing"Table 1 presents a short list of some of the potential "emergencies" in the life of any intensive system. In addition to these, always keep in mind Murphy's Law: "If anything can go wrong, it will!". There is no question that intensive systems need some form of continuous monitoring and alarm system to avoid catastrophic loss of product. In fact, considering the odds, its surprising that any fish survive. In designing a system, it is important not to go overboard in terms of technological complexity and in the shear number of alarms and monitors. Sophisticated alarm systems are of little use, if the hired help continually disarms them due to unreliability, or too many sleepless nights answering false alarms. When designing a system, always keep in mind what the critical water quality requirements are and some sense of their relative importance and required response times. Basically, all a fish needs to survive is water (excluding Chinese catfish and tilapia!). But the water must have sufficient oxygen, be at a proper temperature and not contain too high a concentration of waste products (i.e. ammonia). At high densities, the most important parameter to monitor (besides water) is the dissolved oxygen level. If the water flow or aeration is cut off for any number of reasons, low oxygen and the resulting increased stress levels can lead to disease problems and/or mass mortality within minutes. Thus in designing the oxygen monitoring system, a simple bell may not be adequate, especially if you live 20 minutes away. Some form of backup aeration must be provided for and automatically engaged to insure survival, for the fish and yourself. After dissolved oxygen, other important parameters to monitor are temperature and ammonia levels. But unlike oxygen, temperature changes and ammonia can take several hours to days to reach dangerous levels. Thus there should be time to analyze the problem and take the necessary steps to correct it, in a more relaxed manner. Where to Monitor - "A Question of Importance"Table 2 lists some of the important systems and parameters that need to be monitored in intensive recirculation systems (Huguenen and Colt, 1989). The actual number of functions that are monitored, depend on the specifics of the system and the operating conditions. In some cases, only a few monitoring points may be necessary. In any case, it is important to be sure that your monitoring the "critical" parameter. It helps little to monitor water flow into a tank, if the standpipe has fallen, and water is draining out faster than its coming in! The critical parameter here is water level in the tank. Similarly, there is no advantage in knowing that power is supplied to a pump motor, if the pump is jammed or the motor overloaded and shutdown. What one needs to monitor is whether or not water is being pumped and at an adequate volume for system needs. What To MonitorWater LevelProbably the easiest parameter to measure, water levels are commonly monitored for both high and low levels in production tanks. Other locations to monitor include the intake side of pumps in wells or sumps and should include automatic shutdown of pumps to prevent their damage in the case of low levels. Supple reservoirs or headtanks should be monitored for both high and low levels. High levels can indicate unusual change in normal water demands, due to clogged pipes or valves accidentally turned off. Low levels can be caused by pump or water supply failure. If immersion heaters are used, low level monitoring should be designed to turn them off, to prevent damage. Individual tanks can be monitored to detect plugged drain lines, fallen standpipes or large leaks. Sensors in production tanks need to be located so that passing fish don't accidentally trigger them. Alarm levels should be set so that normal operating transients do not activate an alarm. This can be accomplished either by setting the levels optimistically or allowing some time delay before activating an alarm after a sensor is triggered. In addition, any storage tanks of chemicals (i.e. sodium thiosulfate injection systems) should be monitored to give warning of depletion and also prevent injector pump damage. TemperatureIn any controlled environmental system, continuous and precise monitoring of temperature in rearing tanks is critical in order to optimize production, reduce stress and minimize risk of disease. Usually systems are monitored for both excessive high and low temperature, but it is important to remember that the two are not necessarily of equal importance. While low temperature may reduce growth, excessive high temperature may yield a new career. Since most temperature controllers are cyclic in nature (either on or off), temperature alarm limits should not be set too tight, to prevent unnecessary alarms due to short term transients. If immersion heaters are used, it is a good idea to use several low watt units rather than one single high wattage unit. Then if one unit breaks down, the impact is limited to a single unit and the overall effect is minimized. PressureThe aeration system is one of the most critical components in any intensive system. Response time to failure is very short. Thus if anything is to be monitored and have backup capability, this is it. Air/oxygen pressure is relatively easy to monitor and set up alarms for. Excessive high pressure can indicate blocked supply lines, valves turned off, or clogged diffusers. Excessive low pressure might mean a ruptured airline, open or jammed pressure relief valve, disconnected diffusers or blower failure. Pressure sensors can also be used to monitor the suction and discharge side of pumps. Although it should be noted, that a pressure or suction can exist without necessarily an adequate flow of water to systems. Water FlowIn some cases, the actual measurement of flow rates is important, such as well performance monitoring or chemical injection systems. Normally though, monitoring simply that water which is flowing with an "on-off" device is adequate to insure water supply to critical systems. One such system is in-line heaters. That require a water flow to prevent overheating and potential meltdown. Another is submerged filters, where anaerobic condition can be fatal. Electric PowerPower failure is probably the most common emergency situation and the one most easily monitored. This is especially important when systems (i.e. pumps, filters, etc.) are located some distance from the main building. With three phase electric power, it is quite possible to lose power only in some systems, but not all. This can occur when only one phase is down. Some single phase equipment, dependent upon wiring, can continue to operate. Physical Plant SecurityReadily available, intrusion alarms, smoke and high temperature (i.e. fire) sensors are commonly used to protect against fire, theft and vandalism. Often existing systems can be connected directly to proposed monitoring systems. Water Quality MonitoringCurrently mature technologies exist for on-line monitoring of pH, dissolved oxygen and conductivity. These instruments usually consist of a sensor in the sample flow stream and an electronics/display package. Many models include an integrated alarm circuitry for low or high readings, that can easily be connected to a monitor/alarm system. Other parameters such as ammonia are relatively difficult to monitor on-line, but simple techniques exist for routine grab sample monitoring. How To MonitorWhat follows is a short review of various sensors that can be utilized to monitor system status and performance. Several variations on each are available from multiple sources, most notably the wastewater treatment industry and the chemical and petroleum industry. In most cases, the sophistication and corresponding expense of these types of sensors is not necessarily required in aquaculture facilities. But, until specific equipment becomes available for aquaculture and for high valued products, the added cost can be easily justified. One should keep in mind that in any system, the overall reliability is determined by the most unreliable part (i.e. weakest link). Some idea of relative costs are presented in Table 3. Water LevelFloat Switches. The basic float switch is designed to monitor a single, discrete, preset liquid level. These usually consist of a small permanent magnet encapsulated within a float. The float moves with the water surface, and actuates a hermetically sealed reed switch within the stem or body of the switch. The rugged construction of this design provides for long, trouble free service with minimum maintenance required. Several designs are available for mounting either vertically (top or bottom) or horizontally (side walls) in tanks or sumps. In addition, combining two float switches with a latching relay, allows for differential level control for pump-up or pump-down applications. These are also available as a single rod with floats that ride up and down the rod actuating reed switches inside the rod. Other variations include a single float which is tethered by it electrical cable. A relay inside the float switch is activated depending whether the bulb is floating upward on the surface or hangs down at the bottom. Float switches are simple, foolproof and relatively inexpensive, but they can be easily tripped by a mischievous fish. Optical Liquid-Sensing Sensors These probes detect liquid levels using an internal infra-red circuit. If the probe tip is immersed, light is refracted out into the liquid. If the probe is dry, light is reflected back into a phototransister sensor. Combined with a control module, high or low levels can be monitored and fill or drain operations performed. These are very sophisticated sensor, and somewhat expensive. Non-Contact Ultrasonic Level Sensors. These sensors operate by measuring the exact time required for an ultrasonic pulse to travel to the water surface and return. They are capable of measuring distance (levels) from 0.5 to 30 feet with an accuracy of up to 1% in open air. A variety of outputs are available ranging from alarm relays at preset levels to continuous level data. Expensive, but very flexible in their application. Conductivity Level Switches. These operate on a simple conductivity principle, whereby a small electric current is passed through the conductive liquid when the level reaches the bottom of the electrode sensor. The current can be completed between a single electrode and a grounded metal tank, or between two electrodes. A very simple concept, but somewhat expensive to implement and subject to fouling. Pressure Sensing Level Systems. The measurement of water level is accomplished by mounting a pressure transducer on the discharge side of an air supply, and then measuring the pressure required to bubble air through an immersed pipe in the water column. The pressure required to force the air bubbles out is directly proportional to the depth. These systems are excellent where fouling of float switches could be a problem. Their only drawback is the expense of both the pressure transducers and the signal conversion hardware. TemperatureThe four most common temperature transducers are thermocouples, the RTD, the thermistor, and the integrated circuit sensor. Each is based on some change in the physical property caused by a change in temperature. A thermocouple consists of two dissimilar metal wires jointed together. When heated or cooled, a small electric voltage is generated, that is linearly proportional to the junction temperature. Thermocouples are probably the most versatile temperature transducers available today. Hardware is readily available the performs all the necessary tasks of measuring the voltage and performing the voltage to a temperature conversion. Thus temperature measurements become as easy as twisting two wires together and connecting them to the monitoring hardware. The RTD (resistance temperature detector) takes advantage of the change in resistance of certain metals (platinum, nickel and nickel alloys) as a function of temperature. RTD's are extremely stable and accurate, but also expensive. Like the RTD, the thermistor is also a temperature sensitive resister, composed of semiconductor material. The thermistor is extremely sensitive and able to detect minute changes in temperature, but they tend to be somewhat fragile. The integrated circuit transducer is relatively new. They supply an output (current or voltage) that is linearly proportional to their absolute temperature, and are relatively stable, linear and accurate. Of the four, thermocouples are the easiest to use, but do require the most expensive hardware for signal conversion and compensation. Thermistors are the most precise, over limited temperature ranges, and are most often used in temperature controllers. RTD's have very limited use, because of their high costs. PressurePressure measurements can be used to either maintain pressure at some set-point value (air compressor for control values) or sense that the pressure is moving out of some safe range (high/low alarm). Pressure is defined as a "force per unit area" and this force produces a deflection, distortion or some other physical change. This change can be measured directly using a pressure transducer, and excitation power supply and a signal processor. A pressure control switch employs this proportional deflection to trip an electrical switch at a preset pressure setting. The use of pressure sensors to monitor water depth has already been mentioned. Pressure sensors are not commonly used to measure flow rates, due to the pressure fluctuations created by opening and closing valves in aquaculture systems. The most important system to monitor for pressure is of course the aeration system. Low pressure switches are available in a wide variety of configurations and price scales. It is important to remember, when specifying pressure switches that 1 psig equals 27.68 inches of water. Thus for typical aquaculture systems, the pressure in an aeration system will usually be below 5 psi or 140 inches of water (12 feet). Some pressure switches are rated high enough in load switching capacity, that they can be used directly to activate backup aeration blowers. Others will require some intermediate stage, such as an audible alarm with manual start-up or solid-state or mechanical relays. Flow RatesRotameters. The rotameter operates on the variable area principle, where the fluid flow raises a float in a tapered tube, increasing the area for passage of the fluid. The greater the flow, the higher the float is raised, which is directly proportional to the flow rate. The float reaches a stable position, when the upward force exerted by the flowing fluid equals the downward force exerted by the weight of the float. It is important to note that because of this manner of operation, the rotameter must be vertically orientated. The rotameter has numerous advantages, including: - linear scale Rota meters can be used to measure almost all fluids, over a range of flows from 0.0002 cc/min to 60 GPM. In addition, adjustable proximity switches can be externally mounted on the flow meters, which are tripped at predetermined flow rate. These in turn can activate warning lights, pumps or other equipment. Drag Discs/Paddle/Vane Flow Switches. All of these devices are designed to monitor for flow/no-flow or low flow conditions. Each operates on the drag force of the moving water against a small disk/paddle or vane in its path. They are available in a wide range of flow rates and pipe sizes and often can be externally adjusted for switch point. Normally the drag discs and paddles are installed using a "Tee" fitting, while the vane type is installed in-line. Simple, elegant, inexpensive, but the subject to fouling. Turbine and Paddle wheel Flow Meters. Turbine flowmeters are one of the most widely used technology for accurately monitoring flow rates. Within the turbine flowmeter, the moving water engages a vaned rotor, which rotates at a speed proportional to the flow rate. As the turbine rotates, it can either mechanically indicate flow rate or total flow or electronically generate a pulse that can be sent to other hardware. In a paddlewheel flowmeter, the rotor and blades are perpendicular to the flow, usually mounted in a "Tee" fitting. Paddlewheel flowmeters are very tolerant of particles in the system and a very low cost substitute, where high accuracy of the turbine flowmeter is not required. Where only total flow is required rather than flow rate (GPM), then the turbine meter turns out to be an excellent, low cost solution. Water QualityDissolved Oxygen. There are now a number of dissolved oxygen probes and analyzers available, that are specifically designed for the aquaculture industry. Several newer models are microprocessor-based instruments capable of measuring levels of dissolved oxygen up to 100 ppm (important for monitoring oxygen injection systems). Standard recorder outputs are now provided for both temperature and D.O. that include 4-20 mA and 0-1 VDC, as well as RS- 232 or RS-485 serial output for direct interfacing with microcomputers. Almost all of the newer models include high/low setpoint control relays for controlling external aeration devices, pumps, valves or other equipment (phone dialers). Although the initial investment in this equipment can be high, it must be weighed in terms of the potential loss and poor growth due to low dissolved oxygen levels. pH and Ammonia. Both of these parameters have relatively long response times when compared to dissolved oxygen and other monitored parameters. pH is easily measured with a vast assortment of readily available meters and test kits. On-line ammonia monitoring is feasible, but very expensive and difficult in practice. There is equipment available that can analyze a continuous side stream sample using wet-chemistry and a colorimetric analysis technique. But these techniques are expensive and require frequent standardization and maintenance (Gibbs, 1991). Bringing It All TogetherNow that one can theoretically monitor the recirculation system for many of its potential problems (excluding "Mother Nature's"), the next step is bringing them to the attention of the manager, especially when he's at home asleep. Two systems will be presented, ranging from the simplest (inexpensive) to the more complex (expensive). The choice of system and design is extremely dependent on site specific variables, previously reviewed. Automatic DialersA very inexpensive, simple and versatile monitoring system can be built around several readily available automatic phone dialers/alarm systems. These units originally were designed for home and business security monitoring, but work quite well as a central control unit. One such unit (Sensaphone, Phonetics, Inc., Aston, PA) has been used by several hatchery and recirculation systems with excellent results (Hamilton and Faerber, 1990, Losordo, 1991). The Sensaphone unit automatically monitors the following conditions (Sensaphone, 1990): - AC electric power -- checks for power failure All monitoring is a continuous process. When a problem arises, the unit will announce the alarm condition locally for 30 seconds. If no response is given, it will then sequentially dial up to four user-programmed telephone numbers with an alarm message. It will state, in English, the existing problem, disconnect, and wait for an acknowledging telephone call. It will continue dialing-out until its message is properly acknowledged. One can also call in and receive a status report on the monitored conditions and listen to the background sounds through a built in microphone. For a small operation, such a system might easily manage to monitor adequately all the key operating parameters, for example: air/oxygen pressure, critical water levels and flows, water temperature and dissolved oxygen level. This could be accomplished by wiring several monitoring sensors (normally closed) in series, such that if any one of them is tripped, an alarm is generated. In addition, high sound levels from a fire/smoke alarm would also trigger an alarm. Computer Based Monitoring/Alarm SystemsAt the other end of the spectrum are systems built around sophisticated, dedicated computer based monitoring and data logging systems. (Ebeling, 1991). Over the past few years, several such systems have become available and surely more will follow. One such program is the "Hatchery Management System" (Rutledge Aqua Control, Inc., Snohomish, WA). This program is a computerized system which provides "continuous monitoring, alarm, control, automatic data gathering and analysis and chronology of hatchery event". One important advantage of these types of systems, is that in addition to sounding an alarm, they can also explain to the operator what to do about it. Especially with complex and interconnected systems, this becomes important, to take the guess work and the hunt out of responding to an alarm. Also these systems have the ability to store data over time. Thus giving the hatchery managers the ability to analyze the cause-and-effect relationships between control or adjustment decisions and actual results, allowing fine tuning of future control decisions and increased hatchery efficiency. All of these systems are standard input sensors, such as dry contact binary sensors and low voltage analog sensors and normally 24 VDC output for operating control relays. Keeping It WorkingJust a few final words on overall system design and maintenance. Most of these are taken from Shepherd and Morris (1987) review of practical emergency procedures for fish culturists. System Design- choose sensors carefully to avoid false alarms (fish love to rub against float level sensors) - remember that aquaculture tends to be rather liquid in nature, so protect all electrical connections and equipment from moisture - mount sensors where they are visible and easily accessible for service and adjustment - clearly label the sensor's armed and unarmed modes, preferably with LED's at each station to show sensor status - use the fewest possible sensors - include expansion capability in all components of the system - remember water and electricity make for a fatal combination, use low single voltages (5 VDC, 1 2 VDC or 24 VAC) to protect both the fish and you. Maintenance- have a well prepared maintenance manual - weekly/monthly/yearly maintenance scheduling system and files of major service records - daily/weekly/monthly instrument check sheets - regular system checks, including: - staff training to handle routine alarms - staff familiarization with complete operating system,
including water ReferencesEbline, J. M. 1991. A computer based water quality monitoring and management system for pond aquaculture. pp. 233-248. In: Engineering aspects of intensive aquaculture. Proceedings from the Aquaculture Symposium, Cornell University, Ithaca, New York. Northeast Regional Agricultural Engineering Service, Ithaca, N.Y. Gibbs, C. R. 1991. Advances in on-line water quality monitoring. pp. 304- 321. In: Aquaculture and Water Quality (eds. D. E. Brune and J. R. Tomasso). World Aquaculture Society. Hamilton, S. J. and W. L. Faerber. 1990. Inexpensive monitoring of equipment operation in long-term studies. The Progressive Fish-Culturist, 52:133-136. Hugenin, J. E. and J. Colt. 1989. Design and operating guide for aquaculture seawater systems. Elsevier, N.Y. Losordo, T. 1991. Personal communication. Shepherd. B. G. and J. G. Morris. 1987. A review of practical emergency procedures for fish culturists. Aquacultural Engineering, 6:155-169. Table 1: "Short List" of Potential Problems
Category Area Specifics
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External "Mother Nature" floods, tornados, wind, snow
(Outside your control) ice, drought
"Man electrical outages,brown-outs,
contamination, vandalism /theft
Internal "Staff" operator error
maintenance overlooked, causing
-failure of back-up systems
-failure of system components
automatic controls turned off
alarms deactivated
Water Supply Flow value shut or opened too far
pipe or value plugged
pump failure/loss of suction head
intake screen plugged
Level drain value open
standpipe fallen or removed
leak
overflowing tank
water demand exceeding supply
Quality low dissolved oxygen, high CO2
supersaturated
high/low temperature or pH
ammonia/nitrite/nitrate
other minerals/chemicals/organics
Filters Sand Filters low inflow dissolved oxygen
channeling/caking
excessive head loss
RBC stopped rotating
physically damaged
Trickling Filters physically plugged by organics
channeling
Aeration Blowers motor overheated
drive belt broken
System diffusers plugged/disconnected
Physical Plant Electrical GRIC circuit breakers tripped
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Table 2: Typical Alarm System Monitoring Points
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Water Level supply sumps to pumps (high/low)
drain sumps (high)
headtanks/ reservoirs (high/low)
chemical storage tanks (low)
culture tanks (high/low)
filters (high/low)
Water Flow supply line pumps
submerged filters (low)
in-line heaters (low)
Temperature heating/cooling systems (high/low)
heat exchangers
culture tanks (high/low)
Pressure air pressure in aeration system
suction & discharge side of pumps
intake & discharge side of filters
pressure actuated control values
Dissolved Oxygen culture tanks (low)
inflow to submerged filters (low)
water supply (supersaturated)
Physical Plant Security high temperature/smoke sensors
intruder alarms
Others ozone injection systems
automatic filter backwash systems
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Table 3: Costs of Monitoring Sensors/Transducers/Hardware(These are estimates based on current catalog prices)
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Flow Rate Rotameters (acrylic) $40-250
Turbine Meters $1000-1500
paddlewheel sensors $200-400
Indicator Meters $400-1000
Totalizing Turbine Meters $50-200
Flow Switches Drag diskcs (Tee mounted) $100
Paddle (Tee mounted) $45
Vane (in-line) $40
Level Indicators Float Switches $10-50
latching relays $50-100
Rod high/low controller $200-350
Ultrasonic level $300-1000
Optical probes $100
Controllers $150
Conductivity level switches $120-300
Pressure sensing $500-750
Temperature (Sensors) Thermocouples $10-50
RTD's $100
Thermistors $40-100
Integrated Circuit Transducers $5-20
(Hardware) Thermocouples/monitored point $50-150
RTD's $250
Thermistors $250
Integrated Circuit Transducers $100
Pressure control switches $8-100
measurement hardware $300-500
Water Quality dissolved oxygen probes $150-500
meters $500-1500
pH probes $30-500
meters $200-1000
Automatic phone Dialer $300-3200
Computer Controller Call for Quote
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Sources of Equipment(No endorsement of products by Ohio State University or the author is intended, nor is criticism implied of other manufacturers of similar products which are not included.)
Agriculture Magazine Buyer's Guide Aquatic Eco-Systems, Inc.
P.O. Box 2329 2056 Apopka Blvd.
Asheville, NC 28802 Apopka, FL 32703
(704) 254-7334 (407) 886-3939
(automatic phone dialers, pressure
Canadian Aquaculture Buyer's Guide switches)
4611 William Head Road
Victoria, BC V8X 3W9 Capital Control Co.,Inc.
(604)478-9209 P.O. Box 211
Colmar, PA 18915
OMEGA Engineering, Inc. (800) 523-2553
P.O. Box 2284 (water quality monitoring equipment)
Samford, CT 06906
(800) 826-6342 Hach Co.
(monitoring & control equipment) P.O. Box 608
Loveland, CO 80539
Cole-Parmer Instrument Co. (800) 227-4224
7425 North Oak Park Avenue (instruments & test kits)
Chicago, IL 60648
(800) 323-4340 Island Science
(instrumentation & control equipment) P.O. Box 564
Novato, CA
Keithley Metrabyte (41 5) 898-1422
440 Myles Standish Blvd. (computer software)
Taunton, MA 02780
(508) 880-3000 Ryan Heco Products, Co.
(data acquisition & control plug~in boards) P.O. Box 588
Burbank, CA 91503
Royce Instrument Corp. (818) 841-1141
13555 Gentilly Rd. (control & monitoring equipment)
New Orleans, LA 70129
(800) 347-3505 YSI Inc.
(water quality monitoring Yellow Springs, OH 45387
equipment,automatic (513) 767-7241
phone dialers, computer control systems) (water quality monitoring equipment)
Raco Manufacturing & Engineering Zeigler Bros.,Inc.
Co. P.O. Box 95
1400-62nd St. Gardners, PA 17324
Emeryville, CA 94608 (717) 677-6181
(415) 658-6713 (monitoring equipment & computer
(automatic phone dialers) monitoring)
systems)
Rutledge Aqua Control Systems,
Inc.
P.O. Box 967
Snohomish, WA 98290
(206) 568-2044
(computer software)
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