Continuous monitoring of plant and processes is widely practised but the use of thermal imagers in such systems has always been restricted by camera cost. A radiometric thermal imager can be regarded as equivalent to multiple single point radiometers or a matrix of thermocouples but with the advantages of far denser coverage, non-contact measurement, simpler installation and data processing; in addition several of the advantages of conventional machine vision systems such as shape and position recognition can be provided. IRISYS has developed a multipoint radiometer utilising its low-cost infrared array technology. This unit provides continuous real-time temperature monitoring of 256 data points at an affordable price; it is housed in a small, light-weight, sealed and robust metal case and generates RS232 or Ethernet data output. This paper reviews the radiometer technology and its application to single and multi-camera systems.