for the purposes of promoting an understanding of the principles of the invention , reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same . it will nevertheless be understood that no limitation of the scope of the invention is thereby intended . any alterations and further modifications in the described processes , systems , or devices , and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates . referring to fig1 an apparatus 100 for automatically measuring the soil ph according to the present invention is shown . apparatus 100 includes a probe assembly 110 affixed to a chassis 120 . chassis 120 has a forward side 121 and a rear side 122 , corresponding to the direction in which apparatus 100 moves when collecting data . chassis 120 is supported by one or more wheels 130 , which are adjustably mounted thereto , so as to allow chassis 120 to be raised or lowered relative to the surface of the ground 131 . a tow hitch 140 is affixed on the forward side 121 of chassis 120 , so that the apparatus can be towed by a standard tractor 132 or other appropriate vehicle . a shank 150 is affixed to chassis 120 directing forward of probe assembly 110 , and with the bottom edge of shank 150 positioned lower than the bottom of probe assembly 110 when the apparatus is not collecting data . a removable plate 180 is positioned parallel to the direction of travel , adjacent to the trailing edge of shank 150 , and to the side of probe assembly 110 . a top plan view of the shank 150 / removable plate 180 arrangement is illustrated in fig6 . a water tank 160 is connected by water hoses ( shown as 165 in fig2 ) to a water pump 167 , which is in turn connected to nozzles ( shown as 250 in fig2 ) in probe assembly 110 . in one embodiment , water pump 167 is a standard 12v water pump ( such water pumps being commonly known in the art ). a compressed air tank 170 is connected to an air cylinder ( shown as 230 in fig2 ) though air hoses 175 . preferably , water hoses 165 and air hoses 175 are affixed to chassis 120 at a number of places along chassis 120 . a location sensor 190 is affixed to chassis 120 or other convenient location . in one embodiment , location sensor 190 is a standard global positioning satellite ( gps ) antenna . a computer 199 is affixed to chassis 120 , and is telemetrically connected to water pump 167 , air cylinder 230 , location sensor 190 , and a probe ( shown as 240 in fig2 ), and is programmed automatically to record ph measurements made by probe 240 and location measurements made by location sensor 190 , to correlate ph measurements with the location at which they are made , and to control water pump 190 and air cylinder 230 , as further described below . in an alternative embodiment , water pump 190 and air cylinder 230 are controlled by a separate computer . referring to fig2 further details of probe assembly 110 for making periodic measurements of the ph of soil at a pre - selected depth is shown . the probe assembly 110 includes a sampling platform 210 affixed to a first shaft 211 , which extends through a spring 214 and a mounting 218 , discussed hereinafter . at least the top portion of first shaft 211 is threaded , and is engaged by a threaded nut 216 . the bottom end of spring 214 abuts mounting 218 , and the top end abuts a washer 219 , which in turn abuts threaded nut 216 . an adjustment piece 220 for adjusting the distance between the threaded nut 216 and the air cylinder 230 is provided , comprising two parallel portions , each having a threaded through - hole 221 , and a perpendicular portion . through - holes 221 are oppositely threaded , with the bottom hole threaded appropriately to engage the threads on the top end of first shaft 211 . first shaft 211 and an second shaft 212 engage oppositely threaded through - holes 221 , so that the distance between shafts 211 and 212 can be increased or decreased by rotating adjustment piece 220 about the axis of shafts 211 and 212 . second shaft 212 passes through mounting 228 , discussed hereinafter . the end of shaft 212 opposite to adjustment piece 220 is affixed to air cylinder 230 . air cylinder 230 is adapted to actuate second shaft 212 ( i . e . move the shaft 212 away from air cylinder 230 ) when air pressure is applied by compressed air tank 170 through air hoses 175 . the range of actuation is at least about 5 mm , and preferably does not exceed about 40 mm . air cylinder 230 is affixed to mounting 228 . in one embodiment , the air pressure required to cause air cylinder 230 to actuate shaft 212 is 250 kpa . a probe 240 is affixed to the bottom end of a third shaft 241 . at least the top portion of third shaft 241 is threaded . third shaft 241 passes through a spring 242 , mounting 218 , and mounting 248 . a threaded nut 246 engages the top portion of shaft 241 , and abuts mounting 248 . the top end of spring 242 abuts mounting 218 , and the bottom end abuts mounting 218 . when correctly positioned , probe 240 is just above sampling platform 210 in its retracted position . nozzles 250 are connected to hoses 165 , and are directed toward probe 240 , so that when water is pumped from tank 160 , streams of water contact probe 240 . probe assembly 110 is affixed to chassis 120 by mountings 218 , 228 , and 248 . mountings 218 , 228 are affixed on chassis 120 sufficiently closely to place spring 214 in compression when sampling platform 210 is positioned at least below the bottom edge of shank 150 by turning adjustment piece 220 . mountings 218 and 248 are affixed to chassis 120 sufficiently far apart so as to place spring 242 in compression when probe 240 has been positioned at least as low as the lowest position in which it might be used to make measurements . this allows spring 242 to hold probe 240 in position against jostling of probe assembly 110 during motion . the position of probe 240 can be adjusted by turning threaded nut 246 . in one embodiment , when spring 214 is in tension , it will return sampling platform 210 to the retracted position when air cylinder 230 is at rest ( deactivated ). when air pressure is applied to air cylinder 230 , the compression in spring 214 is overcome , and sampling platform 210 is moved to the extended position . in another embodiment , spring 214 retains sampling platform 210 in an intermediate position when no air pressure is applied to air cylinder 230 , wherein the bottom of sampling platform 210 is above the bottom edge of shank 150 . referring now to fig3 further details of the preferred embodiment of sampling platform 210 are illustrated . sampling platform 210 comprises a tray portion 310 , and support portions 320 . in the preferred embodiment , tray portion 310 is lower in the middle than on the sides . in another embodiment , tray portion 310 is flat . in one embodiment , tray portion 310 is about 50 mm wide , and less than 66 mm long , relative to the direction of motion . support portions 320 are affixed to bar 330 , which is affixed in turn to shaft 211 , so that sampling platform 210 is in mechanical communication with air cylinder 230 . in one embodiment , sampling platform 210 is about 150 mm from the top of bar 330 to the bottom of tray portion 310 . in the preferred embodiment , probe 240 is the sensor of an accumet model 25 ph meter , which is operable to measure the ph of a soil sample when placed in contact therewith . in order to allow its measurement of the ph of the soil samples to stabilize , the probe must remain in contact with the sample for at least 5 seconds , and preferably for 6 seconds . collection of the sample and cleaning of the probe between measurements can be accomplished in about 1 . 5 seconds . therefore , the preferred period of a measurement cycle is about 8 seconds . as will be readily apparent to those skilled in the art , this permits a range of sampling densities to be used , by varying the speed at which the apparatus 100 is moved . when measuring soil ph with apparatus 100 , adjustably mounted wheels 130 are positioned so that the bottom edge of shank 150 is a distance below the point where wheels 130 contact the ground 131 corresponding to the desired depth of measurement , so that , when apparatus 100 is towed , shank 150 will remove soil above the selected depth forward of probe assembly 110 , creating a trench of the selected depth . removable plate 180 prevents upturned soil from falling back against probe assembly 110 , potentially contaminating measurements or otherwise disrupting performance . fig6 is a plan view , illustrating the relative position of shank 150 , sampling platform 210 , and removable plate 180 . air cylinder 230 is adapted to actuate sampling platform 210 between at least two positions , including an extended position and a retracted position . in one embodiment , when air pressure is applied to air cylinder 230 , sampling platform is moved to the extended position , in which sampling platform 210 is brought into contact with the ground 131 , and when air pressure is removed from air cylinder 230 , compression in spring 214 returns sampling platform 210 to the retracted position , in which the soil sample is brought into contact with probe 240 . in another embodiment , air pressure can be applied in two directions to air cylinder 230 , one causing air cylinder 230 to move sampling platform 210 to its extended position , and the other causing air cylinder 230 to move sampling platform 210 to its retracted position . in this embodiment , spring 214 retains sampling platform 210 in an intermediate position when no air pressure is applied . in yet another embodiment , a variable air pressure can be applied to air cylinder 230 so as to cause sampling platform 210 to move to any position intermediate to the extended and retracted positions . furthermore , those having ordinary skill in the art will recognize that any suitable linear actuator device may be used in place of air cylinder 230 , such as a solenoid , stepper motor / lead screw , etc . prior to beginning measurement , sampling platform 210 is positioned by turning adjustment piece 220 so that when air cylinder 230 moves sampling platform 210 to its extended position it is 5 mm below the bottom edge of shank 150 . the tension in spring 214 is optionally adjusted by turning threaded nut 216 . when the apparatus is moving , this will cause soil to be collected on sampling platform 210 . probe 240 is positioned by turning threaded nut 246 so that when sampling platform 210 is moved to its retracted position soil samples contained on the sampling platform 210 are brought into contact with probe 240 . while sampling platform 210 is extended , water is pumped by water pump 167 from tank 160 through hoses 165 , and projected through nozzles 250 onto probe 240 , so as to remove remnants from the previous measurement which might otherwise contaminate the new sample . preferably , water is projected under pressure of at least about 100 kpa . by projecting water onto probe 240 while sampling platform 210 is extended , samples are collected simultaneously to cleaning probe 240 , minimizing measurement cycle time . the operation of water pump 167 and air cylinder 230 is synchronized by computer 199 , which controls the operations of both . computer 199 also records the position of apparatus 100 as measured by position measuring devise 190 while sampling platform 210 is in the extended position . the ph measurement of this sample is recorded approximately 6 seconds later , just before the measurement cycle is completed , and is associated in the data storage device with the position of apparatus 100 when the sample was collected . in this way , the ph data is correctly identified with the position in the field from which the soil sample was taken , and not with the position of the apparatus 100 when the measurement is made , which is later in time , when it will have moved some distance from the sample collection location . referring to fig4 an alternative embodiment of an apparatus for automatically measuring soil ph having a plurality of probe assemblies 110 and corresponding shanks 150 and removable plates 180 is shown . as will be readily apparent to those skilled in the art , by placing multiple probes on a single apparatus , a wider strip of field can be measured at a given sampling density , reducing the number of passes needed to measure a given area . optionally , probe assemblies 110 and shanks 150 are slideably mounted on chassis 120 to permit a variable sampling density . in one embodiment , shanks 150 are independently adjustable , to allow each probe assembly to measure the ph of soil of an independently selected depth . in another embodiment , shanks 150 and probe assemblies 110 are positioned in at least two rows perpendicular to the direction of motion , so that at least two probe assemblies will measure soil from the same strip of soil . in this embodiment , shanks 150 can be adjusted so that shanks in more rearward rows run deeper than those in more forward rows , so that ph measurements can be simultaneously collected for a three dimensional map . in the preferred embodiment , the more rearward rows of probe assemblies can be positioned a distance behind the more forward rows of probe assemblies corresponding to an integral multiple of the sampling interval , such that deeper measurements are made at nearly the same position at which the shallower measurements are made . referring now to fig5 typical sampling densities which can be achieved according to the standard soil mapping methods and the present invention are compared . a field 500 is shown , in which the ph was measured using both the prior art method and the present invention . manually collected measurements 520 show the positions of data points in a ph map created by the prior art method , wherein the sampling density is one measurement per 0 . 5 acres . automatically collected measurements 540 show the positions of measurements made with the apparatus 100 and methods of the present invention , using a single - probe apparatus 100 . while the invention has been illustrated and described in detail in the drawings and foregoing description , the same is to be considered as illustrative and not restrictive in character , it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected .
an apparatus for automatically measuring soil ph at a relatively large number of places in a field , and automatically creating a soil ph map by simultaneously measuring the position of the apparatus and storing the ph data in association with the location from which the corresponding soil sample was taken . the apparatus includes a wheeled chassis , a shank for exposing soil at a controlled depth , a sampling tray for collecting soil , a probe for measuring the ph of the soil , a water supply for cleaning the probe between measurements , a devise for measuring the location of the apparatus , and a computer for controlling the measurement cycle and recording the data .