NT-MDT

Surface potential jump

Technical specifications of surface potential jump:

Range of measured surface potential	± 4800 mV
Sensitivity of surface potential measurement	± 10 mV
Diameter of an electrode	10-15 mm

Surface potential jump meter consists of a sensor of surface electrical potential with electrode of comparison, which are situated on the LB trough frame and a board of surface electrical potential measurement located in the U2 block. The block-diagram of surface electrical potential meter is shown in Fig.1. The electrical circuit of the board of surface electrical potential measuring is shown in Appendix I.

Surface potential jump meter operates the following way. Water phase is connected by galvanization to the “ground” of the system. An electromagnet coil induces an oscillatory movement of vibrating electrode with diameter of 10 - 15 mm. The coil with resistance of 160 Ohm is fed on by generator with frequency that is approximately equal to 150 Hz. The inherent mechanic oscillations of vibrating electrode are about 300 Hz. The armature with the electrode is attracted to the electromagnet coil at any direction of current in it. That is why the mechanic system of the vibrating electrode doubles the frequency. This system is applied to decrease the interference caused by the supplying generator.

Fig.1. Block-diagram of Surface potential jump meter

If the Volt potential of the vibrating electrode and water phase are not equal then at vibrating electrode oscillations alternating current is induced in the external circuit because of the charge redistribution when the capacitance is changing. This current is amplified by current - voltage conversion system and resonance amplifier at frequency of 300 Hz and passes to the phase detector with reference signal of doubled generator frequency. Direction of the signal produced can be changed by phase regulator. After phase detector the signal flows to an integrator with time constant of 1/3 sec. From integrator output the signal passes to a converting input current - voltage of converter. The phase of the reference signal supplying the phase detector is chosen so that a negative feed back is induced, i.e. the Volt potentials at vibrating capacitor plates are equal.
The signal from the integrator output flows to ADC with input resistance of more than 100 kW. The value of Surface potential jump difference on a monomolecular layer is determined as difference the signal at presence of a monolayer and the signal on clean water surface.