Abstract
When electric potential on plant surface is to be measured, a potentiometer with high input impedance is required, because electric potential is very little. A chopper amplifier for a potentiometer with a new DC-AC converter using metal oxide semiconductor field effect transistor (MOSFET) was developed by the authors. The dynamic characteristic of the MOSFETs can be controlled by applying voltage to the substrates, so the MOSFETs are tried on the new amplifier as DC-AC converter. The four electrode type p-MOSFET is used for this chopper amplifier which has the electrode of the sauce, the gate, the drain and the substrate. In this chopper amplifier, the back of two MOSFETs are put together. The substrates of them were connected by each other, and are given square wave voltage. Then the input signal voltage is chopped into square wave and amplified differentially. The trial DC amplifier had very high impedance, more than 3.5 × 1010 Ω and 57 pF in parallel. The electric potential on a living plant surface is desired to be measured with no contact and no infiltrating for the sake of its reproducibility. Therefore conductive sponges were used as electrodes of this potentiometer, because they were made of carbon for a little polarization potential and they adhered easily to plants. Although the output impedance of the standard power source was very high, the input-output characteristic of this potentiometer had a good correlation for input voltage between -1.0 V and + 1.0 V. Surface electric potential voltages of some vegetables and fruits were measured by this potentiometer, and both electric potential voltages changed with time and their preservation ways were examined. From the results, the followings were obtained ;
1. A high impedance potentiometer was designed and constructed for measuring surface potential voltage of living plant tissue.
2. Electrical potential measurement was obtained noninvasively by using the sponge electrode.
3. Correlation between freshness and electric potential voltage on a living plant surface was recognized by the measurements.
4. Preservation in the refrigerator was effective not only for external appearance but for biological and physiological phenomena as well.
