Probe for transcutaneous measurement of blood oxygen content - has combined heating element and temp. sensor connected to measuring bridge

摘要

The measuring probe to give instantaneous measurements of the oxygen content of the blood of a patient, has a head (1) with a temperature dependent resistive element through it which acts both as a heater and as a temperature sensor. This head is connected to a measuring system where the resistance of this element is equalised with a standard resistance so that a heating current is generated which matches a predetermined value. The measuring system is a d.c. bridge across which a diagonal voltage is obtained which is proportional to the difference between the resistances of the element and the standard resistance. This voltage is passed to an amplifier circuit which controls the voltage applied to the element.