Abstract: Arrangement for controlling the cuff pressure in the indirect, non-invasive, continuous measurement of blood pressure in a finger by using a photo-electric plethysmograph in a fluid-filled pressure cuff, an electronic control circuit and an electric pressure valve, the cuff pressure being controlled by the plethysmographic signal in closed-loop operation by means of a servo-reference level, so that the arterial volume is maintained at a pre-adjusted value. For initial adjustment, the cuff pressure or the servo-reference level as initial adjustment quantity is automatically changed continuously in the control range by means of a control waveform supplied to the electronic control circuit, that thereby the peak-through amplitude of the pulsatile plethysmographic signal or cuff pressure signal is detected time and again, and compared with the preceding peak-through amplitude.

Abstract: A bias control circuit for a light-emitting diode having compensation of the light output at changing temperature, in which the light-emitting diode (led) used as temperature sensor is taken up together with a series resistor (R3) in a series circuit to which a fixed supply voltage is applied. A further series circuit of two resistors (R1, R2) having strongly different values is connected parallel across the series resistor (R3) and a differential amplifier (A1) is provided, the one and the other input of which are connected respectively to the junction of the two resistors (R1, R2) and to a setting voltage (Vi), and the output of which is connected to a control means (Tr1) taken up in series with the one series circuit.