Abstract: Method and apparatus for measuring suspended substance concentrations, wherein the method includes measuring the concentration of suspended substances mixed with a liquid by detecting pressure difference between two points distantly located in the depth direction of the liquid, calculating the average density of the liquid between the two points from the pressure difference, and then calculating difference between the average density and a predetermined reference density of the liquid as an index for determining the suspended substance concentration, whereby real time, continuous measurement and easy maintenance and control with high accuracy and wide measuring range are attained.

Abstract: A pressure receiving element for receiving an external pressure is attached to one end of a body and a temperature compensating diaphragm is attached to the other end of the body. A coupling shaft disposed in the body is fixed at both ends to the pressure receiving element and the diaphragm, respectively. A liquid is sealed in the body and means is provided for detecting displacement or force applied to the coupling shaft in accordance with a pressure received by the pressure receiving element. The diaphragm has corrugations of concentric circles and the crests of a plurality of them are made flat and one of the flat crests is fixed to the body. The effective area of the diaphragm inside of the flat crest that is fixed to the body is selected substantially to be equal to the effective area of the pressure receiving element.