Patent Publication Number: US-2005129575-A1

Title: Heavy metals monitoring apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      The benefit of U.S. provisional patent application Ser. No. 60/519,598, filed Nov. 12, 2003, is claimed. The entire disclosure of patent application Ser. No. 60/519,598 is hereby expressly incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      The invention relates generally to the monitoring of dissolved (ionic) heavy metal residuals in liquid process stream or liquid waste (effluent) streams, as examples, after recovery and collection of such metals from a laboratory, medical, industrial or manufacturing process stream.  
      In the United States, the Federal government, through Environmental Protection Agency (EPA) regulations, has issued stringent national compliance standards for the discharge of many heavy metals into sanitary sewers. For example, one such EPA regulation stipulates that no more than 5 ppm silver may be discharged into a sanitary sewer. However, operation of medical X-ray film processing devices, in particular those incorporating photographic fixers, typically generate large amounts of ionic silver and ionic silver complexes as by-products to the photographic process. This is also true for most bleach fix color photo systems, such as those found at photo studios and in photo departments located within retail stores and many of the larger drug stores.  
      Silver recovery units normally are attached to X-ray film and color photo-processors to capture silver from their spent fixer. Over time, such silver recovery units degrade in function and, as a result, it is common for liquids containing 50-1000 ppm silver to be discharged to waste drains connected to municipal sanitary sewers. Even the lower number (50 ppm) within this range well exceeds the EPA-mandated 5 ppm silver limit.  
      For the most part, this mandate has been largely ignored by the medical and photographic communities because heretofore there has been no practical way to monitor the effluent silver in real time or near real time. Without the ability to trace discharges, elimination of ongoing excessive silver through timely and appropriate process equipment changes becomes difficult or impossible. The result has been (and continues to be) silver finding its way to the local Publicly Owned Treatment Works (POTW) (or sewer plant), where it can potentially cause severe problems as a result of the destruction of the many microbiologicals necessary for the proper digestion of human waste material.  
      There are similar problems with monitoring the recovery process associated with other heavy metal waste streams, such as those found in the manufacture of printed circuit boards (copper and silver), batteries (lead), and the electroplating industry (copper, silver, zinc, tin and nickel).  
     SUMMARY OF THE INVENTION  
      In one aspect, a method is provided for monitoring concentration of ions of a specific metal in solution in a liquid process or liquid waste stream. An automatic controller is employed to deliver a sample volume of liquid from the stream to a measurement chamber, adjust the conductivity of the sample volume within the measurement chamber to a predetermined conductivity at a predetermined conductivity measurement temperature, employ an ion specific electrode and a reference electrode to make a voltage measurement representative of the concentration of specific metal ions within the sample volume at the predetermined concentration measurement temperature, record the voltage measurement, and flush the measurement chamber.  
      In another aspect, a method is provided for re-standardizing an ion specific electrode. For predetermined durations, voltages first of one polarity and then of opposite polarity are applied to the ion specific electrode with reference to a re-standardizing reference electrode.  
      In yet another aspect, apparatus for monitoring concentration of ions of a metal in solution in a liquid process or liquid waste stream is provided. The apparatus includes a measurement chamber, a conductivity sensor within the measurement chamber, an ion specific electrode and a reference electrode within the measurement chamber, a controlled sample injection pump for delivering liquid from the stream to the measurement chamber. a controlled ISA injection pump for delivering an ionic strength adjuster liquid to the measurement chamber, a controlled water pump for delivering water to the measurement chamber, and a controller electrically connected to receive signals from the conductivity sensor and from the ion specific and reference electrodes and connected to control operation of the sample injection pump, the ISA injection pump and the water pump. The controller is operable to effect a measurement cycle by directing the sample injection pump to deliver a sample volume of liquid from the stream to the measurement chamber, adjusting the conductivity of the sample volume within the measurement chamber to a predetermined conductivity at a predetermined conductivity measurement temperature by employing the conductivity sensor and the ISA injection pump in a feedback loop, making a voltage measurement representative of the concentration of specific metal ions in the sample volume at a predetermined concentration measurement temperature by employing the ion specific electrode and the reference electrode, and recording the voltage measurement, and flushing the measurement chamber.  
      In still another aspect, a system for monitoring concentration of ions of a metal in solution in a liquid process or liquid waste stream is provided. The system includes a local or client device, and a remote or server computer device. The local device includes a measurement chamber, a conductivity sensor within the measurement chamber, an ion specific electrode and a reference electrode within the measurement chamber, a controlled sample injection pump for delivering liquid from the stream to the measurement chamber, a controlled ISA injection pump for delivering an ionic strength adjuster liquid to the measurement chamber, a controlled water pump for delivering water to the measurement chamber, and a controller electrically connected to receive signals from the conductivity sensor and from the ion specific and reference electrodes and connected to control operation of the sample injection pump, the ISA injection pump and the water pump. The controller is operable to effect a measurement cycle by directing the sample injection pump to deliver a sample volume of liquid from the stream to the measurement chamber, adjusting the conductivity of the sample volume within the measurement chamber to a predetermined conductivity at a predetermined conductivity measurement temperature by employing the conductivity sensor and the ISA injection pump in a feedback loop, making a voltage measurement representative of the concentration of specific metal ions in the sample volume at a predetermined concentration measurement temperature by employing the ion specific electrode and the reference electrode, and recording the voltage measurement, and flushing the measurement chamber. The local or client device also includes a local communications device for transmitting the voltage measurement to a remote location for recording. The remote computer device at the remote location receives and records the voltage measurement.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an overall representation of apparatus embodying the invention;  
       FIG. 2  is a view of the front panel of an enclosure for the electronic subsystem of  FIG. 1 ;  
       FIG. 3  is a functional diagram particularly of components within the fluid-handling subsystem of  FIG. 1 ;  
       FIG. 4  is an enlarged exploded view of the measurement chamber which is part of the fluid-handling subsystem of  FIG. 3 ;  
       FIG. 5  is a representational block diagram particularly of the electronic subsystem of  FIG. 1 , but also including components within the fluid-handling subsystem;  
       FIG. 6  is a diagram, partially in electrical schematic form and partially in block diagram form, of the temperature sensing and conductivity subsystems shown in  FIG. 5 ;  
       FIG. 7  is a diagram, partially in electrical schematic form and partially in block diagram form, of the concentration sensing and heating subsystems of  FIG. 5 ;  
       FIG. 8  is a diagram, partially in electrical schematic form and partially in block diagram form, of various additional control and output subsystems represented in  FIG. 5 ;  
       FIG. 9  is a program flowchart representing Initialization and Main Loop software routines programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 10  is a program flowchart representing a “CALLHOME” software routine programmed within the microcontroller of  FIGS. 5-9 ;  
       FIG. 11  is a program flowchart representing a “SILVERCYCLE” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 12  is a program flowchart representing a “NEWSTAT” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 13  is a program flowchart representing a “HEATUP” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 14  is a program flowchart representing a “HOLDING” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 15  is a program flowchart representing a “CLEARALL” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 16  is a program flowchart representing a “QWIKSTAT” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 17  is a program flowchart representing a “CLEANPROBE” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 18  is a program flowchart representing a “TMPCAPCHRGE” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 19  is a program flowchart representing a “CONDUCTREAD” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 20  is a program flowchart representing a “GETTEMPERATURE” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 21  is a program flowchart representing a “DWELLDELAY” software routine programmed within the microcontroller of  FIGS. 5-8 ;  
       FIG. 22  is a program flowchart representing a “RINSEFILLCYCLE” software routine programmed within the microcontroller of  FIGS. 5-8 ; and  
       FIG. 23  is a program flowchart representing a “DUMPCYCLE” software routine programmed within the microcontroller of  FIGS. 5-8 . 
    
    
     DETAILED DESCRIPTION  
      Referring first to  FIG. 1 , apparatus embodying the invention for monitoring concentration of ions of a metal in solution in a liquid process or liquid waste stream is generally designated  50 . In the embodiment of  FIG. 1 , the apparatus  50  takes the form of a self-contained unit  52 , which is representative of a wheeled cart including shelves (not shown) for convenient and accessible support of various liquid reservoirs described hereinbelow, as well as for mounting of various other subsystems and components described hereinbelow. Moreover, as the self-contained unit  52 , the apparatus  50  is suitable for location within a photo studio or within a photo department located within a retail store, such as a drugstore.  
      In general, apparatus and methods embodying the invention are suitable for analyzing liquid process streams or liquid waste (effluent) streams in a short-term batch process mode so that near real-time data is available to monitor the concentration of heavy metal ions within liquid being discharged to a drain. As described in detail hereinbelow, a microprocessor-based controller stores this data locally and, in a client/server system, sends data by means of an internal modem to a computer site (or sites) within the test facility, as well as to outside locations of choice. Diagnostic information can also be forwarded to a monitoring unit provider (via the same internal modem) to track performance parameters, facilitating the scheduling of timely and appropriate maintenance and/or service work as required. Although the specific embodiment disclosed herein is for monitoring the concentration of silver ions in spent fixer in X-ray film and color photo-processors, the apparatus and methods of the invention are also applicable to measuring the ionic concentration of other heavy metals such as copper, nickel and lead, which are present in other and completely unrelated industries.  
      The apparatus  50  is intended to be employed in combination with a separate processing device, such as a metal recovery device, not specifically shown. As a more particular example, the apparatus  50  may be employed in combination with a silver recovery system attached to a photo-processing unit in order to monitor the discharge from the silver-recovery unit. Moreover, as is described hereinbelow, the apparatus  50  optionally may be configured to positively shut down the operation of the associated equipment in the event heavy metal ion concentration becomes excessive. The apparatus  50  accordingly facilitates the monitoring of the discharge of various heavy metals, such as silver discharged from medical X-ray and color film and photo devices, in a manner that allows the metal recovery apparatus/process to comply with current EPA regulations.  
      The apparatus  50  more particularly includes a hollow cylindrical measurement chamber  54 , a fluid-handling subsystem  56  of which the measurement chamber  54  actually forms a part, and an electronics subsystem  58 . A lower portion of the measurement chamber  54  lies slightly within the housing of the fluid-handling subsystem  56 , simplifying various connections, described hereinbelow, between the fluid-handling subsystem  56  and the measurement chamber  54 .  
      The fluid-handling subsystem  56  is generally contained within a plastic hinged-cover case (not shown), and contains various electromechanical components, in particular, pumps and solenoid valves, described hereinbelow with reference to  FIGS. 3 and 4 , as well as interconnecting tubing. The electronics subsystem  58  likewise is generally contained within a hinged-cover case  60  ( FIG. 2 ), which houses electronic printed circuit boards such as a mother board  62  represented in dash lines in  FIG. 2 , and various components mounted thereon. Included on the mother board  62  is a microcontroller  64  which, in general, directs the overall operation of the apparatus  50  under program control, including in particular the various electromechanical components of the fluid-handling subsystem  56 . The microcontroller  64  and its operation are described in greater detail hereinbelow with reference to  FIGS. 5-8 , and computer program code stored therein is represented in flowchart form in  FIGS. 9-23 .  
      With reference still to  FIG. 1 , three reservoirs are provided, each of corrosion-resistant plastic construction. In particular, there are a sample flow-through reservoir  66 , an ISA liquid reservoir  68 , and an adjust water reservoir  70 . In the embodiment of  FIG. 1 , the reservoirs  66 ,  68  and  70  each have a liquid capacity of five gallons.  
      The sample flow-through reservoir  66  has an input  72  for receiving a liquid process stream or liquid waste stream represented at  74 , as well as an overflow outlet  76  which discharges via an outlet line  78  to a drain line  80 .  
      Thus, during operation, the sample flow-through reservoir  66  remains nearly full of liquid representative of current discharge of the associated equipment, such as photo-processing equipment. Connected so as to enable liquid to be drawn from a lower portion of the sample flow-through reservoir  66  is a sample line  82 , the other end of which is connected to the fluid-handling subsystem  56 .  
      The ISA liquid reservoir  68  contains, and is periodically manually refilled with, an ionic strength adjuster (ISA) liquid appropriate to the chemistry of the liquid stream being monitored, and to the specific metal whose ionic concentration is being monitored. In an apparatus  50  for monitoring the concentration of silver ions in spent photographic fixer, an ammonium thiosulfate solution may be employed as the ionic strength adjuster. An ISA line  84  is positioned so as to draw ISA liquid from near the bottom of the ISA liquid reservoir  68 , the other end of which is connected to the fluid-handling subsystem  56 .  
      The adjust water reservoir  70  contains ordinary tap water piped in via a water line represented at  86 , and has as its primary purpose the warming of potentially cold tap water to a temperature approaching room temperature for adjusting sample electrical conductivity as described hereinbelow, rather than directly using cold incoming tap water for that purpose.  
      The incoming tap water line  90  is connected via a connecting line  88  to a fill control subsystem, generally designated  92 . In the embodiment described herein, the fill control subsystem comprises a pair of level sensors (not shown) within the adjust water reservoir  70  and connected to simple circuitry (not shown) within the electronics subsystem  58  for activating a solenoid valve (not shown) to allow tap water to flow into the adjust water reservoir  70  when the water level falls to the height to the lower sensor, and to deactivate the water fill solenoid (not shown) when the water level within the adjust water reservoir  70  reaches the upper sensor. A mechanical float valve, such as is found within a toilet tank, may as well be employed. As a precaution in the event of malfunction of the fill control subsystem  92 , the adjust water reservoir has a overflow outlet  94 , connected to the drain line  80 .  
      For drawing adjust water as needed from the adjust water reservoir  70 , an adjust water line  96  is connected for drawing water from the near the lower end of the adjust water reservoir  70 . The other end of the adjust water line  96  is connected to the fluid-handling subsystem  56 .  
      Each of the reservoirs  54 ,  68  and  70  includes a “nearly empty” sensor (not shown) connected to circuitry within the electronic subsystem  58  in order to signal that the apparatus  50  should be shut down in the event a liquid necessary for operation is not present.  
      The water line  86  is additionally connected via another line  98  directly to the fluid-handling subsystem  56  to provide rinse water for the measurement chamber  54 , as described hereinbelow. Cold incoming tap water is acceptable for purposes of rinsing the measurement chamber  54 , and conserves the quantity of water warmed to room temperature within the adjust water reservoir  70 .  
      Referring again to  FIG. 2 , the front panel of the electronics subsystem  58  includes an indicator subpanel  100  including a set of monitoring indicators, generally designated  102 , and a set of status indicators, generally designated  104 . The various indicators may take the form of light emitting diodes (LEDs). The monitoring and status indicators  102  and  104  generally reflect operation of the apparatus  50 , and permit an observer to quickly verify proper operation (or not). More particularly, the monitoring and status indicators  102  and  104  show real-time Pass/Fail monitoring information as well as the activity status of all major monitoring functions.  
      The set of monitoring indicators  102  more particularly includes a “good” LED  106 , a “marginal” LED  108  and a “fail” LED  110 . Associated with the “marginal” and “fail” LEDs  108  and  110  are alarm silence pushbuttons  112  and  114 , respectively.  
      The set of status indicators  104  more particularly includes a “sample tank low” LED  120 ; an “H 2 O tank low” LED  122 ; an “ISA tank low” LED  124 , a “probe read” LED  126 ; a “heater on” LED  130 ; an “ISA pump” LED  132 ; an “H 2 O pump” LED  134 ; a “recirculation pump” LED  136 ; a “sample fill pump” LED  138 ; a “drain solenoid” LED  140 ; a “rinse solenoid” LED  142 ; an “H 2 O tank fill solenoid” LED  144 ; and a “power” LED  146 . Connections to various ones of these LEDs are more shown in the partial electrical schematic diagrams of  FIGS. 6-8  described hereinbelow.  
      Also visible in  FIG. 2  is the front panel  150  of a conductivity controller  152 , described in greater detail hereinbelow with reference to  FIG. 6 . The microcontroller  64  and the conductivity controller together comprise an automatic controller.  
      With reference now to  FIGS. 3 and 4 , in the illustrated embodiment the measurement chamber  54  more particularly takes the form of a hollow cylindrical column, oriented vertically, made of PVC plastic, as an example. The plastic material may be either clear or opaque. The cylindrical measurement chamber  54  is approximately four inches in diameter and fourteen inches tall. The measurement chamber or column  54  has a base  160  generally including various apertures and conduits through which liquid enters and exits as described hereinbelow, as well as a top  162  including apertures for various probes, likewise described hereinbelow. A large aperture (not shown) is cut into the top of the fluid-handling subsystem  56  housing (not shown) for receiving the measurement chamber  54 , and the base  160  is conveniently attached to the top of the fluid-handling subsystem  56  housing by bolted ferrules (not shown).  
      Internal to the measurement chamber  54  is a float switch  164 , the function of which is to act as a fill control device for both sample and flush water charges. A Model M8000 float switch made by Madison Manufacturing Company may be employed.  
      The measurement chamber  54  has two drains, a main drain  166  centrally located in the base  160  and controlled by a drain solenoid valve  168  connected to a drain line  170 , as well as a precautionary overflow tube or drain  172 , connected directly to the drain line  170 . The sample level controlled by the float switch  164  is purposely kept slightly below the overflow drain  172  to allow headspace for ISA fluids needed for conductivity adjustment. However, flushwater is allowed to purposely reach slightly above the overflow drain  172  so as to thoroughly clean out the entire chamber  54  inside surface. This is accomplished by programming that adds a few additional seconds of flushwater inlet “ON” time beyond the normal float-controlled “OFF” time.  
      Liquid primarily enters the measurement chamber  54  through four ports or openings within the base  160 . More particularly, these are a sample input port  174  supplied by a sample pump  176  which draws from the sample flow-through reservoir  66 , an ISA inlet port  178  supplied by an ISA pump  180  which draws from the ISA liquid reservoir  68 , and an adjust water inlet port  182  supplied by an adjust water pump  184 , which draws from the adjust water reservoir  70 . Gorman-Rupp Model 16000-124 Bellows pumps may be employed. In addition, there is a rinse water or flush water inlet  186  which is supplied through a rinse solenoid valve  188  directly from the water line via the  FIG. 1  connecting line  90 .  
      In order to maintain a flow of liquid past various sensing electrodes described hereinbelow, required to maintain the proper operation thereof, a recirculation loop  190  is provided, including a recirculation pump  192 , a recirculation liquid inlet  194 , and a recirculation return  196 . A Gormann-Rupp Model EX315-432 centrifugal pump is used in the disclosed embodiment, but any pump of similar size and performance specifications may be employed.  
      Projecting into the measurement chamber  54  through respective apertures in the top  162  are four probes, each described in greater detail hereinbelow with reference to  FIGS. 6 and 7 . These are a conductivity probe  200  which passes through an aperture  202 , an ion-specific electrode  204  which passes through an aperture  206 , a reference electrode  208  which passes through an aperture  210 , and a re-standardizing reference electrode  212  which passes through an aperture  214 . As shown in greater detail in  FIG. 6 , the conductivity probe  200  includes a pair of spaced conductivity-sensing electrodes  216  and  218  to which AC voltage is applied, as well as a temperature sensing element  220 , preferably a resistance temperature detector (RTD).  
      Finally, an electric heater  222  is mounted to the base  160 , and projects into the measurement chamber for heating a sample volume of liquid contained therein first to a predetermined conductivity measurement temperature, and sub subsequently to a predetermined concentration measurement temperature.  
      In operation of the apparatus  50  as thus far described, under control of the microcontroller  64 , which activates the sample pump  176 , a precisely metered volume of liquid from the sample flow-through reservoir enters the measurement chamber  54  until signaled by the float switch  164 . This delivers a sample volume of liquid to the measurement chamber  54 . The conductivity of the sample volume within the measurement chamber  54  is adjusted to a predetermined conductivity at a predetermined conductivity measurement temperature, employing the conductivity probe  200  in separate temperature control and conductivity control feedback loops. Although it is possible for the predetermined conductivity measurement temperature to simply be the ambient temperature within which the apparatus  50  is being operated, preferably the heater  222  is employed to heat the sample volume up to a temperature of, for example, 23.5° C., as the predetermined conductivity measurement temperature. The conductivity of the sample volume is adjusted to a conductivity which is consistent with the conductivity of the liquid stream being sampled. As an example, for color bleach fixers, the predetermined conductivity may be 55.0 milli-Siemens per centimeter. More particularly, the conductivity is adjusted by operation of the conductivity controller  152 , operating in combination with the microcontroller  64 , which together, as the automatic controller, operate the ISA pump  180  and the adjust water pump  184 , to deliver quantities of ISA liquid and possibly adjust water from the ISA liquid reservoir  68  and the adjust water reservoir  70 , as required.  
      When conductivity adjustment is completed, the sensing electrodes  216  and  218  of the conductivity probe  200  are electrically disconnected and shorted together in order to prevent them from influencing the subsequent ion concentration measurement. To allow all stray voltages to dissipate from the AC voltage applied to the conductivity sensing electrodes  216  and  218 , there is a 60-second delay before a routine begins which involves employing the ion-specific electrode  204  and the reference electrode  208  to measure concentration of the ions of the specific metal. At the beginning of the concentration measurement routine, the liquid within the measurement chamber  54  is heated a second time, for example to 24.25° C. The ion-specific electrode typically requires time to achieve voltage stability, and a five-minute sample dwell time is inserted to allow the voltage measurement to become stable. Just prior to making a voltage measurement to acquire data, the heater  216  is operated for a third time, to bring the temperature of the liquid within the measurement chamber  54  to the predetermined conductivity measurement temperature, in this embodiment, 25° C. The temperature sensor  220  within the conductivity probe  200  is employed in each case to sense the temperature to determine when the heater  222  should be de-activated.  
      During this entire time, the recirculation pump  192  operates to maintain a flow of liquid past the ion specific and reference electrodes  204  and  208 , respectively. Recirculation provided by the pump  192  is important to more quickly blend the relatively low volume of conductivity adjustment liquids into the relatively higher volume of sampled liquid already present within the measurement chamber  54 , enabling the measurement process to proceed more quickly and efficiently.  
      In addition, as described hereinbelow with reference to  FIG. 7 , the ion-specific electrode  204  is periodically re-standardized.  
      Under control of the microcontroller  64  aided by the conductivity controller  152 , which together serve as the automatic controller  154 , these steps briefly described hereinabove are repeated at period intervals.  
      It is good practice to flush out the complete fluid system the measurement chamber  54  and recirculation loop  190  several times, especially if small (parts per billion) (ppb) levels are to be detected. In the example of monitoring silver ion concentration, it takes very little contamination by a prior ppm Ag liquid to contaminate a system in ppb Ag. Experience has shown that, regardless of starting residual silver left in the system after dumping, seven to ten water flushes clears out the Ag+ion down to undetectable levels. Multiple flushing also offers the side of minimizing the build-up of solid waste precipitates which could eventually foul the sensors, leading to erratic sensor readings.  
      For this reason, under microcontroller  64  program control, the measurement chamber  54  and recirculation loop  190  preferably are flushed out totally at least seven to ten times between cycles, seven times where “parts per million” (ppm) Ag limits are in effect, but at least ten times when the silver limit is expressed in “parts per billion” (ppb). The Gorrman-Rupp Model EX315-432 high-volume centrifugal pump employed as the recirculation pump  192  aids in rapidly flushing the system, to minimize downtime while the system is being flushed.  
      To protect the somewhat delicate sensor heads from drying out (thus rendering them inoperable), the operational cycle is set up to start with the measurement chamber  54  full of water. Thus, the last flushwater remains within the measurement chamber  54  until the “time to take a reading” programming sub-routine is reactivated.  
      With reference now to  FIG. 5 , the microcontroller  64  in the illustrated embodiment is a TFX-11v2, manufactured by Onset Computer Corporation, Bourne, Mass. The TFX-11v2 includes a number of digital I/O ports, as well as a number of 12-bit A/D converter input ports, program memory and data storage memory. Programming within the microcontroller to effect various functions described herein is represented by the flowcharts of  FIGS. 9-23 , and those  FIGS. 9-23  should be referred to for additional details. A number of subsystems are connected to and controlled by the microcontroller  64 . For convenience of illustration, the various subsystems are somewhat arbitrarily represented in  FIG. 5  as boxes  240 ,  242  and  244 , which represent the separate  FIGS. 6, 7  and  8 , respectively. In each of  FIGS. 6, 7  and  8 , a portion of the input and output lines of the microcontroller  64  are illustrated. It will be appreciated that the combination electrical schematic and functional block diagrams of  FIGS. 6, 7  and  8  for purposes of illustration omit a number of conventional interfacing components. For example, various digital outputs of the microcontroller  64  are buffered through field-effect transistors (FETs) (not shown).  
      The block diagram of  FIG. 5  also includes a local modem through which the microcontroller  64  transmits data. The local modem is connected via a telephone line represented at  248  to a remote modem  250  connected to a remote computer device  252 , which serves as a data-recording file server, and may be off site.  
      With reference to  FIG. 6 , the conductivity controller  152  more particularly comprises a Eutech Model Con200 conductivity controller. However, any similar single-point two-relay conductivity controller with equal or better performance specifications may be employed. The temperature compensation function of the Eutech Model Con200 conductivity controller  152  is not employed. Instead, the temperature sensor  220  (which is part of the conductivity probe) and heater  222  are employed separately, under control of the microcontroller  64 , to heat the sample volume to the predetermined concentration measurement temperature.  
      A suitable conductivity probe  200  is a Phoenix Electrode Model 2771314-31-003T Conductivity Probe. However, any conductivity probe with a Cell Constant of 1, a built-in 32K RTD temperature sensor, and having equal or better performance specifications may be employed.  
      The conductivity controller  152  more particularly includes a pair of probe terminals  260  and  262  which are connected to the conductivity-sensing electrodes  216  and  218  within the conductivity probe  200 . The Eutech Model Con200 conductivity controller  152  applies a low voltage AC to the conductivity sensing electrodes  216  and  218  via the probe terminals  260  and  262  and measures the resultant current flow in order to determine conductivity. The conductivity controller  152  has a pair of analog output terminals  264  and  266  which drive a current representative of measured conductivity, in addition to providing a display output on the  FIG. 2  front panel. This conductivity-indicating current output is converted to a voltage drop across a resistor  268 , and sensed via an analog input  270  of the microcontroller  64  for data logging purposes.  
      The Eutech Model Con200 conductivity controller has a pair of relay outputs  272  and  274  having normally-open contact of respective relays  276  and  278  internal to the conductivity controller  152 . In the illustrated embodiment, a common pole of the relays  276  and  278  is connected at  280  to a +12 volt supply.  
      During operation, the conductivity controller  152  activates the relay  276  when more ISA fluid is required in order to increase the conductivity of a sample, and the relay  278  when water is required to decrease the conductivity of a sample. Water may be required to correct a slight “overshoot” in the injection of ISA fluid.  
      Operation of the conductivity controller  152  is enabled by the microcontroller  64  so that operation of the conductivity controller  152  occurs only at appropriate times. Accordingly, the microcontroller  64  has digital outputs  282  and  284  connected (through appropriate buffers, not shown) to activate respective relays  286  and  288 . The contacts of the relay  286  are arranged so as to connect the conductivity sensing electrodes  216  and  218  to the probe terminals  260  and  262  of the conductivity controller  152  only when the relay  286  is activated, and to otherwise entirely disconnect the conductivity sensing electrodes  216  and  218  from the rest of the circuitry and to short the two electrodes  216  and  218  together. Similarly, contacts of the relay  288  are arranged so as to operationally connect the relay outputs  272  and  274  of the conductivity controller  152  only when the relay  288  is activated.  
      More particularly, the relay output  272  is connected, through contacts of the relay  288 , to drive a DPST relay  290 . One pole of the relay  290  is connected to drive the “ISA pump” LED  132 , and the other pole is connected to drive a solid state relay  292 , which in turn energizes the ISA pump  180  which operates at 117 volts.  
      Likewise, the relay output  274  is connected through contacts of the relay  288 , to drive a DPST relay  294 . One pole of the relay  294  is connected to drive the “H 2 O pump” LED  134 , and the other pole is connected to drive a solid state relay  296 , which in turn energizes the adjust water pump  184 .  
      In addition, so that the microcontroller  64  can monitor and record the times when the ISA pump  180  and the adjust water pump  184  are operated, a pair of optical couplers  298  and  300  are also connected to the output of the solid state relays  292  and  296 , respectively, and drive digital inputs  302  and  304  of the microcontroller  64 .  
       FIG. 6  also represents circuitry for interfacing for the temperature sensor  220  to an A/D converter analog input  306  of the microcontroller  64  for temperature measurement purposes. More particularly, temperature measurement circuitry  308  includes a resistor network  310  and an appropriate amplifier circuit  312  having an input  314  and an output  316  connected to the microcontroller  64  analog input  306 . Operation of the temperature measurement circuitry  308  is enabled by operation of a DPDT relay  318  controlled by a digital output  320  of the microcontroller  64 . The contacts of the DPDT relay  318  are arranged, when not energized, to ground the input  314  of the amplifier  312 , and to entirely disconnect the resistor network  310  and the temperature sensor  220  from the circuit. When activated, the contacts of the relay  318  are arranged so as to apply +5 volts to the resistor network  310 , and connect an output of the resistor network  310  to the input  314  of the amplifier  312 .  
       FIG. 7  represents circuitry for connecting the ion-specific electrode  204  and the reference electrode  208  to a 12-bit A/D converter analog input  350  of the microcontroller  64  for conductivity measurement purposes. A low-noise amplifier and signal conditioning circuit  352  has a pair of differential inputs  354  and  356  which receive and amplify the voltage across the electrodes  204  and  208 , which voltage represents the concentration of specific metal ions within the sample volume. The amplifier circuit  352  has an output  358  connected to the microcontroller  64  analog input  350 . In addition,  FIG. 7  shows circuitry for re-standardizing the ion-specific electrode by applying a voltage first of one polarity then of opposite polarity to the ion-specific electrode  204  with reference to the re-standardizing reference electrode  208 .  
      Three relays, a 4PDT relay  362 , a 4PDT relay  364  and a DPDT relay  366 , activated by respective digital outputs  368 ,  370  and  372  of the microcontroller  64  are employed to set up different operational states. When all three relays  362 ,  364  and  366  are deactivated, the ion-specific and reference electrodes  204  and  208  are shorted to each other and electrically disconnected from the circuit through contacts of the relays  364  and  362 . The re-standardizing reference electrode  212  is entirely electrically disconnected from the rest of the circuitry. Inputs  354  and  356  of the amplifier  352  are connected to circuit ground via contacts of the relay  362 .  
      To measure the voltage between the ion-specific electrode  204  and the reference electrode  208 , which voltage is representative of the concentration of specific metal ions within the sample volume, the microcontroller  64  activates the 4PDT relay  362 , which electrically connects the electrodes  204  and  208  to the inputs  364  and  366  of the amplifier  368 . The resultant voltage is then recorded by the microcontroller  64  as a Test Voltage.  
      More particularly, a software routine executes which, in the case of Test minus Control (T-C) data, subtracts the Test Voltage from its paired Control voltage, and the resultant Test minus Control (T-C) voltage differential is then entered into a ppm vs diferential voltage calibration equation, which converts this differential voltage value to ppm silver. However, when using the Known Addition voltage measurement protocol, the actual Test measured voltage is entered into a ppm silver vs silver sensor voltage calibration equation, which directly converts the Test measured voltage into ppm silver.  
      For reference purposes, these data are stored within the server program ( FIG. 6 ) permanently, but yet can be accessed anytime. A phoneline datalink and programming furnished to customers allows customers to access the data on their own computers in many formats, but typically displayed as a graph of ppm Silver versus Time (in days, weeks, or months).  
      To re-standardize the ion-specific electrode  204 , the microcontroller  64  first activates the DPDT relay  366  which, in combination with the contacts of the relay  364 , connects the re-standardizing reference electrode  212  to circuit ground and the ion-specific electrode  204  to the output of a +3 volt power supply  376 , for about three seconds. A contact of the relay  364  also drives the “Probe Clean” LED  128 . Then, to apply a voltage of opposite polarity to the ion-specific electrode  204  with reference to the re-standardizing reference electrode  212 , the relay  366  is activated, in addition to the relay  364 , thereby connecting the ion-specific electrode  204  to circuit ground, and the re-standardizing reference electrode  212  to the output of the +3 volt power supply  376 .  
      Due to a limited number of output lines of the microcontroller  64 , the digital output  372  is also employed to activate a relay  380  which has contacts arranged to drive a power relay  382  which in turn drives the heater  222 , in addition to contacts arranged to activate the “heater on” LED  130 .  
       FIG. 8  represents connections of four additional digital control outputs of the microcontroller  64 , for activating each of the sample pump  176 , the recirculation pump  192 , the rinse solenoid valve  188  and the drain solenoid valve  168 . Digital outputs  390 ,  392 ,  294  and  296  of the microcontroller  64  activate respective DPST relays  400 ,  402 ,  404  and  406 . One pole of the relay  400  is connected to drive the “Sample pump” LED  138 , and the other pole is connected to drive a solid state relay  410 , which in turn energizes the sample pump  176 . One pole of the relay  402  is connected to drive the “Recirculation pump” LED  136 , and the other pole is connected to drive a power relay  412 , which in turn energizes the recirculation pump  192 . One pole of the relay  404  is connected to drive the “Rinse Solenoid” LED  142 , and the other pole is connected to drive a power relay  414 , which in turn energizes the rinse solenoid valve. Finally, one pole of the relay  406  is connected to drive the “Drain Solenoid” LED  140 , and the other pole is connected to drive a power relay  416 , which in turn energizes the drain solenoid valve  168 .  
      The microcontroller  64  additionally has “marginal” and “fail” digital outputs  420  and  422  which can optionally be employed to shut down an associated process in the event measured concentration exceeds predetermined limits. These outputs are connected to a user-operable switch  424  which selects one or the other to drive an output relay that can be used to shut down the associated equipment, such as a photo-processor.  
      The embodiment described herein is particularly for measuring the concentration of silver ions, and the ion specific electrode  204  accordingly is a potentiometric half-cell responsive to the concentration of silver ions. A Model AGS1501-003B Silver/Sulfide ISE sensor available from phoenix Electrode Company may be employed. As the reference electrode  208 , another ion specific electrode or potentiometric half-cell which is specific to ions which are not expected to be present in the stream from which the sample volume is taken advantageously may be employed. In the disclosed embodiment, a Model F001501-003B Lanthanum Flouride ISE sensor, also available from phoenix Electrode Company is employed as the reference electrode  208 .  
      As the re-standardizing reference electrode  212 , a stainless steel rod may be employed.  
      Standard statistical techniques are used to remove all wild points from the data collected for all Test samples. An “average value” is then calculated for each of these samples. These average values are then corrected, if necessary, for minor aberrations in temperature and/or conductivity, and converted to ppm silver (by a previously generated silver volts-to-ppm silver equation. If that ppm Silver value falls within the pre-set limit (say 5.0 ppm), then the system is considered performing within spec, the number is sent by modem to an off-site file server and stored in a file against a date &amp; time stamp.  
      However, if the value obtained is outside the limit, then in addition to being stored in the mainframe server file, that particular value also enters a special file that tracks “out-of-limit” performance. In order for an “Out-of-Limit” notification to be given, this sub-routine must recognize at least three “out-of-limit” values in sequence; otherwise the sub-routine resets itself. This “Three Strikes and your Out” approach ensures that the customer never receives a false positive indication.  
      Actually, contained within this sub-routine is yet another sub-routine that requires three valid “out-of-limit” indications before that “Strike” is validated. Therefore, with this approach, there must be at least nine valid “out-of-limit” responses before an “Out-of-Limit” notification is given. This technique is not the same as just nine “out-of-limit” values in sequence, because any one “within-limit” value merely resets that particular strike, but all strikes validated ahead of this strike remain in place.) This technique minimizes false alarms.  
      Also, four or more sequential “within-limit” values reset all Strikes, the assumption being that whatever the problem was has been corrected. Of course, even if this resetting were to take place, the individual “out-of-limit” data is not lost to the customer, as each of these points would show up on any historical PPM Silver vs Time plot, should one be generated that covers that particular time and date.  
      An especially good technique to use where very small ppm silver levels are to be monitored (say 1 ppm or less) is the use of Standard Addition (also called Known Addition), where a small amount of a known silver solution is added to the sample, followed by a second reading, after the voltage has re-stabilized in the mixture.  
      The volume and concentration of the standard must be carefully chosen to meet the following criteria: 
          1) The concentration and volume of the additive must be sufficient to cause a significant and measurable change of the measured voltage of the sample solution, but the volume must also be small enough so that it does not cause a significant change in the sample Ionic Strength.     2) The volume of the additive must be large enough so that volumetric errors are not significant.        

      Both of these criteria are easily met with the disclosed system, with appropriate programming, enabled by toggling a “Known Addition Activated? Yes/No” flag upon system startup.  
      An advantage of using this technique is that both test and control measurements are made while the electrodes are continually immersed in fluids sharing the same (or very nearly the same) temperature and Ionic Strength.  
      While specific embodiments of the invention have been illustrated and described herein, it is realized that numerous modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.