| 摘要 |
PURPOSE:To hold the fertilizer concentration of a culture solution constant by providing an AC bridge circuit which includes a couple of the 1st electrodes at an interval in the flow passage of the culture solution and a couple of the 2nd electrodes in a small chamber, and a phase detector for detecting an unbalance output of the AC bridge circuit. CONSTITUTION:The culture solution is circulated between a culture solution tank 1 and a culture rack and plants are cultivated while the fertilizer concentration of the culture solution is monitored. When the liquid level in the culture solution tank 1 falls as the culture solution is consumed, a liquid level detector 4 operates to open the 1st solenoid valve 7, so that water begins to be supplied. Then when the liquid level rises up to a specific level and the liquid level detector 4 turns off, the 1st solenoid valve 7 is closed and the supply of the water is stopped. On the other hand, when the culture concentration of the culture solution drops below the reference concentration of the culture solution in the small chamber 9, a phase detector 19 generates an output to open the 2nd solenoid valve 8, thereby supplying an undiluted fertilizer solution from an undiluted fertilizer solution tank 6. |
