Under control of a computer, the Scanivalve can be directed to take
pressure readings of all the ports or an individual port. The input pressures
range from 0-26 psi which correspond to a head ranging from 0-60 feet of water.
Calibration of the Scanivalve was performed using a standard Dead Weight tester.
Results showed an accuracy of 
1 inch of
water head (see Figure 5).
The Scanivalve pressure transducer output is an analog voltage ranging from 0-10 V
dc. This voltage is converted to 12 binary bits using a Vector Graphics analog to
digital converter. "Port" identification is effected through an optical encoder
having a BCD (Binary Code Decimal) output.
3.2.2 Sand Measurement in Well Discharge
Sand Measurement in the well discharge is performed by a HIAC unit
particle counter. In this system, particles of material in a sample stream of water
pass through a 20 to 1000 micron sensor and are scanned by a collimated light beam.
A photodiode coupled with advanced electronic circuitry counts individual particles.
Resulting calculations of mechanical grading analysis and particle flow rates in parts
per million (ppm) are easily determined.
Figure 4
Figure 5
The particle counter sensor is located close to the well (see
Figure 6). A small flow is diverted from the well above the
regulating butterfly valve. Output from the sensor is relayed to the HIAC particle
counter where a BCD output of channel number and cumulative particle counts is read
by the computer. Range is satisfactory for the size of particles produced from
typical aquifers.
Figure 6
Figure 7
3.2.3. Computer Instrument Interface
During any one data logging cycle, over 1100 bit of information on
pressure and particle counts are relayed by a data multiplexer to the computer for
storage and analysis. The multiplexer interfaces input data in an orderly fashion,
enabling the computer to "read" all information through one 8-bit parallel input
port (see Figure 7).
3.2.4. Control Computer
The heart of the data acquisition system is a 32K byte microcomputer
manufactured by Northstar. The peripheral devices include two "mini-floppy" dual
density single-sided disk drives with a 256K storage capability. Communication to the
computer is through a SOROQ video display station. Hard copy output and graphic
plotting of results is accomplished using an Integral Data Systems dot matrix
printer.
A real time clock circuit external to the computer was built to
keep track of "time of day" necessary for the automatic data logging operation.
