Optics. Reflective (mirror) and refractive (lens) optics are used in non-contact temperature sensors to isolate and define radiation from the measured target.
Field of View. The field of view (FOV) is expressed in degrees solid angle or radians. The FOV allows easy calculation of the minimum target size for each working distance. A convenient measure is the distance-to-target ratio, e.g., 20:1, indicating a minimum target of 1 inch at a 20 inch measuring distance.
Focusing on Target. Optics in non-contact temperature sensors are generally of the fixed-focus type. Focusing at longer measuring distances is not required if the target area is larger than the entrance aperture (lens diameter) of the instrument.
Small Targets. For miniature objects, fixed-focus close-up optics are used, and the minimum target size is specified. Targets as small as 0.5 mm can be isolated.
Fiber Optics. Fiber optics permit a physical separation of the lens assembly from the detector and signal processing electronics in restricted spaces or hostile environments. The useful measuring range of fiber optics starts at 400°C (750°F). Minimum target areas are as defined above.
Target Scanning. Reflective surface mirrors are used to change the viewing angle of the measuring sensor if direct viewing is difficult or impractical. An oscillating mirror can be employed to deflect the intercepted radiation and to scan a predetermined temperature profile across a target area. A sequence of scanned temperature profiles taken at pre-set spatial intervals over the target can be displayed as a thermal image or in the form of a thermal map.
Aiming on Target. A variety of optical aiming techniques are used with non-contact temperature sensors:
Simple bead-and-groove gun sights,
Integrated or detachable optical view finders,
Integrated or detachable light beam markers.
Signal Processing. A variety of outputs are typically available in a radiation thermometer.
Direct Output. Non-contact temperature sensors convert the intercepted thermal radiation into an electrical signal proportional to the spectral radiance emitted from the target surface.
Linearized Output. An electronic network converts the thermal radiance signal into an electrical current/voltage proportional to temperature.
Sample and Hold. The momentary temperature reading, selected by an external trigger, is held (frozen) until replaced by a new value in the next sampling cycle.
Maximum Value or Peak Hold. The highest temperature reading over the specific measuring period is displayed. Reset is triggered by an external signal.
Minimum Value or Valley Hold. The lowest temperature reading during a specific measurement period is displayed period is displayed. Reset is triggered by an external signal.
Peak to Peak. The difference between the maximum and the minimum temperature readings during a specific measurement period is displayed.
Speed of Response. Short response time is needed to follow rapidly changing dynamic temperature processes. Long response time integrates all signal variations during a specific measurement period and enhances temperature resolution in order to average changing values or to improve measurement precision.
Alarms. An output signal (relay) is activated when the signal reaches a preset temperature value. Two independent set points--HI/LO--are generally provided.