Reflective (mirror) and refractive (lens)
optics are used in non-contact temperature
sensors to isolate and define radiation from
the measured target.
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.
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.
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.
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 400C (750F). Minimum target areas are as
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
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.
on Target. A variety of optical aiming
techniques are used with non-contact
- Simple bead-and-groove gun sights
- Integrated or detachable optical view
- Through-the-lens sighting
- Integrated or detachable light beam
variety of outputs are typically available in
a radiation thermometer.
Output. non-contact temperature sensors
convert the intercepted thermal radiation into
an electrical signal proportional to the
spectral radiance emitted from the target
Output. An electronic network converts the
thermal radiance signal into an electrical
current/voltage proportional to temperature.
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.
Value or Peak Hold. The highest
temperature reading over the specific
measuring period is displayed. Reset is
triggered by an external signal.
Value or Valley Hold. The lowest
temperature reading during a specific
measurement period is displayed period is
displayed. Reset is triggered by an external
to Peak. The difference between the
maximum and the minimum temperature readings
during a specific measurement period is
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.
An output signal (relay) is activated when
the signal reaches a preset temperature value.
Two independent set points--HI/LO--are
Coolable Jackets. Water cooling extends
ambient temperature range up to 400C (752F) or
Purge Fittings. Lens barrels or
attachments with fittings for compressed air
are designed to direct a clean air flow across
the lens surface. They keep the optical sight
paths free of vapor, fumes, and dust.
cavities controlled at a homogeneously
distributed temperature serve as blackbody
simulators for the calibration of radiation
thermometers. To accommodate the variety of
instruments, the calibrators provide an
effective aperture of ~ 1 in. (25 mm), which
is wider than most targets. Each calibrator is
optimized for a specific operating temperature
- Stirred Water bath: 30--100°C
- Aluminum core: 50--400°C (122--752°F)
- Stainless steel core: 350--1000°C
- Portable, battery operated field
calibrator: fixed temperature choices from
40°C to 100°C (104--212°F)
Instruments. These devices are generally
used for continuous process monitoring and
control. They are available in low- and
high-temperature models, each with its own
Instruments. Portables are typically
favored for process checks,
preventive/predictive maintenance, thermal
surveys, R&D, and temporary temperature
monitoring. The low- and high-temperature
versions differ in performance.