S25 TO-18

S25 Detector circuit overlay

A single-channel silicon-based thermopile that offers the smallest single element active area size at 0.25mm x 0.25mm in a small TO-18 package. Delivers a very fast 12ms time constant in Argon encapsulation gas and even faster with Neon gas at 9ms. Delivers a very low Temperature Coefficient of Responsivity of -0.04%/°C.

Excellent for non-contact temperature measurement when extremely small spot size is a design requirement.

Small active area, fast time constant in a small package with lower output that has a higher cost.


  1. See Standard Windows and Filters (PDF) for list of optical filter options
  2. See Thermopile Configuration Table for more options.

For more detailed information see the datasheet S25 TO-18 (PDF).

Specifications apply at 23°C with KBr Window and Argon encapsulating gas.

Parameter Min Typical Max Symbol Units Comments
Active Area size   .25 x .25   AA mm Hot junction size, per element.
Number of Junctions   20       Per element.
Output Voltage   24   Vs μV DC, H=330μW/cm2 (3)
Responsivity   111.5   V/W DC, =Vs/HA (2)
Temperature Coefficient of   -.04     %/°C Best linear fit, 0° to 85°C (1)
Noise Voltage 17.2 19.4 21.4 Vn nV/√Hz Vn2=4kTR
Detectivity   1.44   D* 108√Hz/W DC, D*=Vs/ VnH√A (2)
Field of View   88°/103°   FOV Degrees See Assembly Drawings for FOV Description.
Operating Temperature -50   100 Ta °C  

General Specifications:
Flat spectral response from 100nm to > 100µm. Linear signal output from 10-6 to 0.1W/cm2.
Maximum incident radiance 0.1W/cm2 , damage threshold ≥ .5W/cm2Notes:
(1) Parameter is not 100% tested. 90% of all units meet these specifications.
(2) A is detector area in cm2.
(3)Test Conditions: 500K Blackbody source; Detector active surface 10cm from 0.6513cm Diameter Blackbody Aperture.* Protected by U.S. Patent No. 5, 059,543 and U.S. Patent No. 5,100,479

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