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      Introduction

      The Nutrimax Control System was developed some years back long before the IOT etc. became a thing. Working with Okkie van Niekerk, we developed a groundwater conditioning system which could work remotely by adding a mixture of three acids to a groundwater feedline to control the pH in a continuous process.

      nutrimex

      The dilution feed water flow (shown at the top right) is fed with a mixture of Nitric, Sulphuric and Phosphoric acids into the mixing tank. The acid proportions are controlled to suit the raw groundwater properties.

      The mixed solution is then added to the groundwater feed line to keep the pH in a predetermined range. The system has local control with SMS reporting of events and notification when an acid fee tank runs low.

      Proof of Concept

       We embarked on the development of the control and monitoring system using most of our own hardware in the most economical way. The primary components used was our Measurement and Control Interface (a multi-I/O serial interface device), a single-board PC running windows, a GSM communications module and a variety of other custom and standard components.

       The test system with two 1000 l tanks and multiple venturis and control valves.

      The test enclosure with flat panel screen display and internal components.

      The I/O list:

      Connection Type Function
      Analogue Inputs  
      1 Main Water Line pH
      2 Main Water Line Temperature
      3 Dosing Mixture Conductivity
      4 Pressure (not fitted)
      5 Internal Enclosure Temperature
      6 Mains Status
      Digital Inputs
      Din 1 Mixing Tank Level High Switch
      Din 2 Mixing Tank Level Low Switch
      Din 3 Main Pump Status
      Din 4 MCI Enclosure Door Status
      Relay Outputs
      Relay 1 Nitric Acid (HNO3) Feed Valve 1
      Relay 2 Nitric Acid (HNO3) Feed Valve 2
      Relay 3 Phosphoric Acid (H3PO4) Feed Valve 1
      Relay 4 Phosphoric Acid (H3PO4) Feed Valve 2
      Solid State Relay Outputs
      SSRout1 Acid Dosing Pump
      SSRout2 Watchdog Lamp
      Digital Outputs
      Dout 1 Sulphuric Acid (H2SO4) Feed Valve 1
      Dout 2 Sulphuric Acid (H2SO4) Feed Valve 2
      Dout 3 Dilution Valve
      Dout 4 Acid Dosing Valve
        All the parameters are logged periodically and then condensed into a single SMS message when an event occurs.
      Event Number
      1 Main Pump On After the Main Pump On Delay has expired but sends time the pump started.
      2 Main Pump Off When Main Pump switches off - a summary of activity for the irrigation cycle.
      3 pH Alarm Sends message when high or low alarm level exceeded - used with start-up delay to pH can stabilize.
      4 Acid Conductivity Alarm Sends this when the conductivity at the end of any acid addition cycle is outside the acid conductivity range.
      5 Dilution Conductivity Alarm Sends this when the conductivity during any dilution cycle is outside the dilution conductivity range.
      6 Enclosure Temp Alarm Sends message when high or low alarm level exceeded.
      7 Mixing Tank Filling Alarm Sends message when it takes too long to fill to the mixing tank.
      8 Enclosure Door Opened Sends message when the enclosure door is opened.
      9 System Rebooted Sends message when program starts up

       

      The program works using a basic 1 second counter (in this case maximum count of 300) and the various valves are switched on or off as determined by the configuration setup. Most parameters can be setup and then logged and used to operate the system automatically.

      Level switches are used to determine the liquid levels in the tanks and venturis are used to add the various acids.

      SMS messages are used to compress and send all the relevant data and VNC can be used to remotely access the display screen and the logged data.

      A collection of display screens is shown below:

       

      Typical Data Log:

      0.000717592592592593      38005      671      650      180      -259      335      669      669      669      0      1      32      4482
      0.00141203703703704      38005      669      650      181      -259      336      669      669      668      0      1      32      4480
      0.00210648148148148      38005      673      650      181      -259      335      669      669      668      0      3      32      4488
      0.00280092592592593      38005      669      650      186      -259      336      671      669      668      0      7      32      4512
      0.00349537037037037      38005      671      650      185      -259      336      671      669      668      0      7      32      4544
      0.00418981481481481      38005      671      650      183      -259      335      671      669      668      0      6      32      4481
      0.00488425925925926      38005      669      650      181      -258      336      671      669      668      0      6      32      4544
      0.0055787037037037       38005      671      650      185      -259      334      671      669      668      0      4      32      4484
      0.00627314814814815      38005      669      650      180      -259      336      671      669      668      0      0      32      4496
      0.00696759259259259      38005      669      650      186      -259      335      671      669      668      0      0      32      4544
      0.00766203703703704      38005      671      650      180      -259      334      671      669      668      0      1      32      4482
      0.00835648148148148      38005      671      650      181      -258      335      671      669      668      0      1      32      4544
      0.00905092592592593      38005      669      650      181      -259      334      671      670      668      0      3      32      4488

      Typical Event Log:

      19-Jan-04 08:20:43 "Enclosure Door Opened"  650      672      178      -2587      322      12676      4      193      0
      19-Jan-04 08:22:46 "Dilution Conductivity Fault"  650      671      180      -2562      323      12544      0      144      0
      19-Jan-04 08:22:58 "Main Pump On"  650      667      180      -2562      323      12544      0      129      0
      19-Jan-04 08:23:48 "System Restarted"  650      667      178      -2575      321      12546      1      32897      0
      19-Jan-04 08:24:08 "Acid Conductivity Fault"  650      669      177      -2575       321      12546      1      137      0
      19-Jan-04 09:23:07 "Dilution Conductivity Fault"  650      667      185      -12      282      12736      2      145      0
      19-Jan-04 09:29:51 "Dilution Conductivity Fault"  650      665      186      -2537      279      12736      4      145      0
      19-Jan-04 09:44:57 "Dilution Conductivity Fault"  650      665      191      9300      276      12736      3      145      0
      19-Jan-04 09:49:11 "pH Alarm"  650      137      192      3775      276      12673      6      133      0
      19-Jan-04 10:00:03 "Dilution Conductivity Fault"  650      -20      208      10050      276      12608      6      149      0
      19-Jan-04 10:30:38 "Enc Temp Alarm"  650      -20      191      1925      1013      12552      7      165      0

      Typical SMS Message:

      0829000575, RoBuSST 1: 19-Jan-04 16:23:23 # Acid Conductivity Fault# pH=6.6(6.5|22.6) EC=1016 EncT=29.6  N2 S1 P1 MTFC= 0 EW=  137 DIO=0011:0001:0100:0000"