at any location on any one of the four sides walls of the conduit as well as outside the conduit the prior art on the other hand has only two possible mounting configurations e g up down and left right instead of measuring the amount of energy or light blocked by flowing material as prior art sensors mass flow sensor 10 of the present invention measures the amount of energy reflected by the flowing material in this respect detectors 58 60 receive energy reflected back from the conveyed material passing through the flow passage of conduit 20 and convert the energy into a corresponding electrical signal indicative of the amount of energy detected as explained below by measuring the amount of energy reflected back to the detectors the mass flow sensor of the present invention offers the significant improvements previously discussed namely reduction in the requirement of constructions materials minimization of installation complexity and improvement in system accuracy the mass flow sensor of the present invention may also include a means of temperature control as previously described the mass flow sensor uses leds as light sources and photodiodes as detectors while stability of both is very important to sensor accuracy temperature affects their operation therefore a temperature control system may be used to maintain constant temperature inside the mass flow sensor keeping the sensor temperature constant improves sensor accuracy the temperature control system not shown generally comprises a temperature sensor a reference voltage a voltage comparator a solid state relay and a thermo electric module the particular method of maintaining constant temperature inside the sensor i e heating cooling or a combination of both is not critical so long as the temperature inside the.