Thermopiles are thermocouples arrays that are wired in series and used in motion sensing applications. They are relatively simple in design and are built to perform non-contact temperature measurements. Thermopiles or thermocouple arrays are thermal flux meters that consist of a thin, continuous layer of conductor and semiconductor material. Typically, this material is covered on one or more surfaces with a thin deposit of copper. A 32 x 32 array of tiny thermopiles senses thermal energy and detects infrared (IR) radiation. The remote measurement of multiple points allows the thermocouple array to build a multi-dimensional image. Thermopile sensors detect the absolute amount of emitted thermal energy and generate a proportional thermoelectric voltage. A thermopile sensor uses standard connectors and can measure a wide range of temperatures. Thermopiles are relatively inexpensive and often available as a thermopile detector.
Metal type is an important consideration when selecting thermopiles. Base metal thermopiles can measure different temperature ranges, depending on the sensor material. Each type or designation represents a specific metal type and temperature range. Type E (chromel/constantan) has a typical temperature range of -270° C to 1000° C. Type J (iron/constantan) has a temperature range of -210° C to 1200° C. Type K (chromel/alumel) has a temperature range of -270° C to 1372° C. Type N (nicrosil/nisil) has a temperature range of -270° C to 1300° C. Type T (copper/constantan) has a temperature range of -270° to 400° C. For noble and refractory metals, choices include type B (platinum 30%/rhodium) with a temperature range of 0° C to 1820° C; Type S (platinum 10%/ rhodium) with a temperature range of -50° C to 1768° C; Type R (platinum 13%/rhodium) with a temperature range of -50° C to 1768° C; and Type W (tungsten/rhenium) with a temperature range of 0° C to 2300° C.