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Voltage, Current, and Light Intensity Interface Board
This product is designed to monitor the voltage and current produced by a wind generator, solar panel, or other DC generator - or the voltage and current consumed by a DC load; it also has an interface for light intensity sensor.The Wind Data Logger has four 0 to 5 volt analog input channels. The Voltage, Current, and Light Intensity Interface Board conditions the following inputs:
- Voltage Monitor: 15 to 40 volts DC (24 volt nominal version -- 12 volt nominal version coming soon)
- Current Monitor: -20 to 20 amps (60 amp momentary survival)
- Light Intensity: 0 to 1800 watts per square meter using Davis Instruments 6450 Solar Radiation Sensor
Features
- 3"x3"x1" circuit board with four 1/8" mounting holes.
- Current and voltage input connector accommodates 10 AWG to 30 AWG wire (in, ground, out)
- Current and voltage input protected from accidental shorts
The board connects to the "Temperature Sensor" jack on the Wind Data Logger using a standard CAT5 patch cable. A second jack is provided for passing the temperature sensor signal through the board. The third jack on the board is used by the solar radiation sensor. The signal from this board show up on the Wind Data Logger LCD and in the columns of data recorded on the memory card.
Technical Details and Theory of Operations
Bill of Materials
There are three separate sections of the circuit board. The voltage monitoring circuitry, the current sensor, and the light sensor power supply.
24V Voltage Monitoring Circuitry
The voltage monitoring circuitry is the most complicated section. The incoming voltage is run through a 50mA self-resetting fuse to protect the circuit board in the event of a short. It is then fed into a voltage divider. For the 24 volt version, the voltage divider is dividing the voltage by 8 using 91k and 13k 0.1% resistors. The output of the voltage divider is run into a op-amp buffer to provide a low impedance drive. The output of the buffer amp is run into a voltage difference amplifier that subtracts 1.8 volts. The 1.8 volt offset is to set 14.4 volts of input to be equal to 0 volts output -- effectively shifting the range of the 0-5 volt Wind Data Logger input to 14.4 to 40 volts (14.4/8-1.8=0). The final stage of amplification is used to multiply the signal by 1.56 so that 14.4 to 40 volts covers the 0 to 5 volt range of the Wind Data Logger ADC. The transfer function for the voltage section is:
where Vout is the output voltage and Vin is the input voltage to the board
Current Sensor
The current sensor is a wonderful single chip hall effect current sensor. The chip has a range of -20A to 20A which yields a ratiometric output from 0.5V to 4.5V. Each amp through the chip yields a 100mV change in output. 0 amps through the sensor produces 2.5 volts. The transfer function of the current sensor is:
where Vout is the current sensor voltage output and Ip is the current through the sensor.
Light Sensor Interface
The light sensor is a Davis Instruments 6450 Solar Radiation Sensor / Pyrnamometer. The sensor needs 3V +- 10% and ground and it provides a voltage that is proportional to the light intensity. Each watt per square meter of solar radiation generates 1.67mV (0.00167V) of output. The output can be fed directly into the Wind Data Logger, so all that is needed is a power supply for the sensor. The LM1117-3.3 and two 100uF capacitors provide a regulated 3.3 volt supply to the sensor.More information on the Davis Instruments 6450 can be found at: