Skin potential measuring sensor

skin potential measuring sensor

The invention relates to a skin potential sensor comprising a measuring electrode to be placed on the skin and a signal transmission element connected thereto.

When measuring skin potential and transmitting measured values ​​analogously, a special cable is required to minimize capacitive and inductive interference induced by the environment. If unshielded electrode cabling is used, error signals are induced in the cables from external sources of electromagnetic interference. The error signals may be larger than the skin potential signal itself. Due to interference protection, the cables must therefore be individually shielded and therefore the cable system becomes complicated, heavy and expensive. The movement and bending of the shielded cable, in turn, causes interference when the cable sheath moves relative to the cable conductor and the insulator 15 (so-called cable microphone). When a high-impedance signal is transmitted in a long conductor, the cable resistance, capacitance, and inductance cause changes in signal amplitude as well as frequency response. Different skin potential signals can also interfere with each other in the cable system (so-called translucency).

The object of the invention is to provide a skin potential sensor which eliminates the drawbacks associated with current skin potential sensors and in particular the problems caused by error signals and interference protection. In particular, it is an object of the invention to provide a skin potential sensor which can be connected directly to a digital data processing system via a digital data transmission system.

The object of the invention is achieved by a skin potential sensor which is characterized by what is stated in the claims.

In the skin potential sensor according to the invention, measuring, processing and digitizing parts of the signal are placed in the immediate vicinity of the measuring electrode in order to convert the signal given by the measuring electrode into digital. By placing the signal measuring, signal processing and digitizing parts 35 in the immediate vicinity of the electrode according to the invention, the measured analog skin potential signal can be converted directly to digital without transmission cables. When the measurement is made directly from the electrode, the numerical signal can be reliably transmitted in conventional cables and the errors caused by the cables can be eliminated. Therefore, expensive special cables are not required.

The signal transmission means is arranged to transmit the measured signal in digital form via a data transmission network to the main processor. Thus, the skin potential sensor can be connected directly to a digital data processing system.

In one embodiment of the invention, in a system formed by several sensors, the measurements of the measurement signals of the different sensors are arranged to take place simultaneously. Simultaneous measurements allow numerical calculation of different signals (e.g., summation and difference). Numerical further processing enables the generation of new signals computationally (without additional electronics) from signals measured from several different sensors. If measurements are not taken simultaneously, the calculated signal may be severely distorted.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 shows a block diagram of a digital skin potential sensor according to the invention, Figure 2 shows an application of digital skin potential sensor 25 electronics, and Figure 3 shows a block diagram of a multi-sensor system.

In the block diagram of Figure 1, part 1 is a measuring electrode on the skin surface. From the measuring electrode, the signal is applied to a part 2, which includes a buffer amplifier which prevents the loading of the high-impedance electrode signal. Part 3 includes high-pass and low-pass filtering of the signal, which filters out interference signals outside the measuring range as well as the electrode offset voltage. Part 4 confirms the signal large enough. Part 5 converts the analog signal to digital 35 and Part 6 includes digital signal processing and an interface to the communication network. Part 7 contains the cabling of the data transmission network.

In the circuit according to Figure 2, the operational amplifier A1 forms a buffer amplifier which prevents the loading of the high impedance signal.

The gain of the buffer amplifier is +1. Capacitor C1 and resistor R1 form a high-pass filter. Resistor R2 and capacitor C2 form a low-pass filter. Filters eliminate interference outside the measuring range. The operational amplifier A2, together with the resistors R3 and R4, forms an amplifying non-inverting amplifier with which the signal is amplified sufficiently. The gain of the amplifier stage can be calculated from the formula G = (1 + R3 / R4). IC1 is an A / D converter that converts an analog signal to digital. Resistor R5 fine-tunes the gain and R6 fine-tunes the zero level. IC2 is a microprocessor that controls the conversion and possibly analyzes the signal. IC3 forms buffer stages on the communication bus.

In the block diagram of Figure 3, several skin potential sensors are connected to each other. Parts 8 and 9 are digital skin potential sensors, part 10 is a potential equalizing ground potential and part 11 is a mains control unit controlling the network, which may have a display 12 and a keyboard 13.

The main processor unit controls the digital sensors via the data transmission network and collects the data provided by them. The collected and possibly analyzed data can also be transferred to other systems via the communication section 14.

The invention is not limited to the applications presented, but may vary within the scope of the inventive idea formed by the claims.