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Microprocessor Instrumentation Systems

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Although an earlier version of the Point Load Tester was manufactured with a digital display readout in engineering units, its measurement system used an analogue design that was unable to correct for small variations in the loading frame that occur under load.  In addition, the operator was required to manually record the displayed results and more time was lost transcribing these results into computer database records in the office.

In conjunction with a local distributor, a redesign of the system was undertaken incorporating a Phillips microprocessor, to evaluate the potential of this type of design.  The features built into this instrument can be readily incorporated into the majority of measurement systems and may be used as a guide to the potential of the concept.

  • Load calibration linearized over 5kN range segments

  • Load output in kN-force or lb-force units

  • Alpha-numeric display of instrument serial no identification, load values, operating modes, configuration options, previous peak load values, lo-battery state warnings

  • Membrane keypad front panel switches

  • Automatic zero at beginning of each test

  • Auto-off configuration for power saving

  • Auto-shutdown from computer interface option

  • Auto-rotation option for instrument menu selection

  • Automatic recording of the last five peak load test values for operator recall as required

  • On-line remote display of all instrument functions with the option of recording peak value test results directly to data file

  • Tab separated data file format directly compatible with commercial spreadsheet applications


The AMEC transport assembly operates under the supervision of the control system to lift the array of eight sensors that determine the change in vertical position of magnetic targets embedded in fill material surrounding a 76mm diameter access tube.

A Phillips microprocessor was used to control the operation of the stepping motor that rotates a precision ball-screw to lift the sensor array in steps of 0.016mm.  The state of each of the eight sensors is checked at each step increment and the 'step count' recorded as each sensor is triggered by its respective target.

The transport assembly communicates with the control system via an IC interface transferring all scan information to the main system at the completion of each scan.  In addition, status information on the quality of the scan, the state of the sensor array and the system temperature is monitored and transferred to be recorded as part of the total scan data package.  The transport processor also has a number of independent diagnostic features available to facilitate field service requirements.


The control section of the AMEC system is based on the Phillips microprocessor chosen for its on-board UART and analogue-to-digital port capacity.  This device was coupled with a battery backed RAM module incorporating integrated clock and calendar alarm features.   This allowed the entire AMEC system to stay in a low power sleep mode until woken to complete its measurement cycle.

In addition to its supervisory role of the transport assembly, the control system processor monitors power supply levels, system power consumption and provides data storage, data retrieval, data transmission, system diagnostics, program options, site identification and serial communication functions with the outside world.

The control system can also interface to a maximum of eight vibrating wire piezometers for measurement of ground water levels in the vicinity of the settlement position.  The incorporation of this feature into the control system case meant that a second data-logger was not required at considerable cost saving.   The control system has been designed to operate from a number of power sources including external batteries, solar power and 120/240V AC supplies.