Abstract: An electronic control circuit for carbonated beverage dispensing machines employs the low voltage AC supply for the solenoid dispensing valves as a source of clipped, balanced ac which is applied to one or more water-imersed sensors. One sensor senses ice mass size and the other senses carbonated water supply level. The balanced ac prevents electroplating by the sensors. Peak detector circuits associated with the sensors produce dc control signals whose levels increase and decrease respectively as the control shut-off point is reached. These dc control signals are applied to Schmitt circuits, the output of one of which is used to control the carbonated water supply pump and the other of which inversely controls the refrigerant compressor. In addition, the balanced ac signal is used to clock a counter which is held at full count.

Abstract: An improved electronic coin validator responsive to detect a plurality of different denominations of valid coins. The validator is constructed around a microcomputer (60). A single coil (30) in the tank circuit of an oscillator is used to determined content. The output of the oscillator is rectified (111, 112) and filtered (115, 116) to give an output signal (120) having a magnitude proportional to the envelope of the oscillator output. An improved diameter detection arrangement using only two LED/optodetector pairs (32, 132, 35, 135) is used to determined diameter by determining the actual average velocity of the coin as it travels down the runway by the sensors and thus to calculate a chord length using the calculated average velocity and a time period (T3) measured as the coin passed the sensors. A plurality of vend prices may be set by the state of a plurality of dip switches (69) and the microcomputer also provides control signals (150, 156) to a laundry machine.

Abstract: A multiplexed circuit for selecting one of a plurality of vertically spaced resistance temperature devices (RTDs) in a fluid storage tank. An electronic multiplexer is used to select a particular one of a plurality of vertically spaced RTDs to be connected to circuitry for reading the output value of same. The device is used in connection with an intelligent field interface device (FID) at the tank. The FID contains a table storing values for expected ranges of output values from the RTDs. When a value actually read is out of range, the FID causes the multiplexer to select another RTD for reading. The arrangement also allows reading of temperatures at various levels within the tank, irrespective of the actual fluid level.

Abstract: Apparatus for operating a motor driven device and testing the state of a limit switch in series with the motor, in the environment of a field interface device in a tank farm is disclosed. During operation of a relatively high power relay (115), a latched (145) signal ties one side (130) of the two-wire circuit to ground through a low impedance (139). When testing of the state of a series limit switch (119) is needed, the same supply voltage is switched onto one side of the two-wire circuit (147) but the low side of the two-wire circuit is grounded through a relatively high impedance (135, 136) to prevent sufficient current for operating the relay coil (117) from flowing. The presence or absence of current through the high impedance is detected through a coupling device (137) which provides a logical one or zero on an output line (68) to determine whether the limit switch is open or closed.

Abstract: An intelligent field interface device for use in a fluid storage facility is disclosed. A bidirectional standard serial communication bus (20) provides communication between a plurality of the interface devices (17) and a central location (18). Surge and lightning protection (50, 51) as well as a high degree of electrical and magnetic isolation (45) are provided between the power supplies of the system. Each device includes a local one chip microcomputer (35) which has a field set address (56) and communicates through optoisolation (27) with the bus through a UART (28). Analog multiplexing (40) of RTD outputs (176-179) or outputs of other transducers (162) is provided to a local to analog to digital converter (36) so that all measured tank parameters may be transmitted digitally back to the control location. An arrangement for both testing and operating a motor operated valve (110) through a two-wire circuit (141, 132) including a limit switch (119) is also shown.