Model 1375 Thermistor Detector

The Servo Model 1375 Immersed Thermistor IR Detector is designed for use in sophisticated infrared applications that require superior long wavelength capabilities from an uncooled detector.

Description

The thermistor detector is a thermal detector where the absorption of optical or infrared energy leads to a temperature rise. Since the thermistor has a very large negative temperature coefficient of about 4%/^oC, a large voltage responsivity results when the detector is appropriately biased. The thermistor detector can also be used over the entire wavelength range of UV to far IR since the temperature rise is dependent on the energy absorbed and not the photon wavelength directly.

The Model 1375 Immersed Thermistor IR Detectors have been developed to satisfy the requirements of a broad range of applications requiring high reliability and ruggedness. Active element size, resistance,time constant, immersion lens material and capsule configurationcan be tailored to specific application needs. Normal tolerances are ± 10% on active element size, ± 200 Ohms on resistance (with a ± 5% resistance match between the active and compensator elements), and ± 20% on the time constant. Applications include Railroad Hot-Box Detection Systems, Industrial temperature Measurement, Earth Sensors for Space Applications and Radiometers. 

Standard Configurations:

Effective Element Size: 0.4 m x 0.4 mm, ± 10%

Nominal Element Resistance: 0.25 Megohms, ± 20% (BTL #2 material)

Time Constant: 2.0 to 3.0 milliseconds (1/e)

Responsivity (@600C, 15 Hz BW): 100 volts/watt, open circuit

N.E.P. (@600C, 1Hz BW): 8x10-9 watts/cps^1/2

Wavelength Response: Determined by lens and AR coating

Immersion Lens Material: Germanium hemisphere

Operating Bias: Approx. 20 volts/element (specified with each unit)

Bolometer Field of View: ± 30^o min., to half power points for f/l system

Anti-reflection Coatings: Finished detector can be coated for specified peak wavelength

Packaging: Stainless Steel

Custom Designs

Servo Corporation has extensive experience in the development of custom designed components, assemblies and arrays to meet any particular detector and optical system requirements. SERVOTHERM immersed thermistor IR detectors offer the optimum balance of performance characteristics within the present state-of-the-art.

In custom designed detectors, the key variables are element size, time constant and resistance. Once these parameters are specified, all remaining characteristics can be established. Immersed thermistor IR detectors have an effective element size which is larger than the actual element size. The increase in effective size is determined by the index of refraction of the immersion material and its geometry.