S25 TO-5

S25 Detector circuit overlay

S25 TO-5 Thermopile Detector

A single-channel silicon-based thermopile that offers the smallest single element active area size at 0.25mm x 0.25mm in a TO-5 package. Delivers a fast 18ms 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 with lower output that has a higher cost.


  1. See Standard Windows and Filters (PDF) for list of optical filter options
  2. Internal aperture precisely defines active area for applications with FOV and/or spot size requirements. See Aperture Options (PDF) for available sizes.
  3. See Thermopile Configuration Table for more options.

For more detailed information see the datasheet S25 TO-5 (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.
Element Area   .0625   A mm2  
Number of Junctions   20       Per element.
Number of Channels   1       Per detector package.
Output Voltage 35 40 45 Vs μV DC,  H=330μW/cm2 (3)
Signal-to-Noise Ratio 1,636 2,062 2,616 SNR √Hz DC, SNR=Vs/Vn
Responsivity 169.7 193.9 218.2 V/W DC, =Vs/HA  (2)
Resistance 18 23 28 R Detector element
Temperature Coefficient of   -.04     %/°C Best linear fit, 0° to 85°C (1)
Temperature Coefficient of  R   -.11     %/°C Best fit, 0° to 85°C (1)
Noise Voltage 17.2 19.4 21.4 Vn nV/√Hz Vn2=4kTR
Noise Equivalent Power .08 .10 .13 NEP nW/√Hz DC,  NEP= VnHA/Vs (2)
Detectivity 2.0 2.5 3.2 D* 108√Hz/W DC,  D*=Vs/ VnH√A  (2)
Time Constant   18   Τ ms Chopped, -3dB point (1)
Field of View   69°/76°   FOV Degrees See Assembly Drawings for FOV Description.
Package Type   TO-5       Standard package hole size:Ø.150"
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/cm2

(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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