Minimum Specifications and Spots

 L3Harris | Minimum Specifications and Spots

Tubes with a model code UM (Unlimited FOM Military) and UA (Unlimited FOM Aviation) have differing tolerances for dark spots.
  • UM tubes limit spots that are >.003" to Zone 2 and 3. Spots that are >.003" are not permitted in Zone 1.
  • UA tubes limit spots that are >.003" to Zone 3. Spots >.003" are not permitted in Zone 1 or 2.
Dark spots </= .003" are permitted in both UM and UA tubes and are not countable in any Zone. Spots that are  </= .003"are colloquially referred to as peppering. Niether UM or UA tubes permit spots larger than .009".

 

Military Spec

Performance summary:

L3 Unfilmed White Phosphor | 18UM:

  • SNR: 24.1 minimum
  • FOM: 1540 minimum
  • Center Resolution: 64 lp/mm minimum

L3 Unfilmed White Phosphor | 1610 tubes (2376+ FOM models of PVS-31A, 1531):

  • SNR: 33 minimum
  • FOM: 2376 minimum
  • Center Resolution: 72 lp/mm minimum

Spot summary: 

No spots >.003" are allowable in Zone 1. Max spot size of .009". While spot sizes and quantities per zone are listed below, there's a max of 4 spots allowed per tube which are limited to Zone 2 and Zone 3. 

Spot Size Zone 1 Zone 2 Zone 3
(Inches) Limit Limit Limit
>.012 0 0 0
>.009 0 0 0
>.006-.009 0 1 1
>.003-.006 0 2 2
Bright Spots 0 0 0
Dark spots </= .003” are acceptable

 

 

Aviation Spec

Performance summary:

L3 Unfilmed White Phosphor | 20UA:

  • SNR: 28 minimum
  • FOM: 1792 minimum
  • Center Resolution: 64 lp/mm minimum

L3 Unfilmed White Phosphor | High FOM, 36 SNR min:

  • SNR: 36 minimum
  • FOM: 2304 minimum
  • Center Resolution: 64 lp/mm minimum
  • Exceeds 24UA
Spot summary: No spots that are >.003" are allowable in Zone 1 or Zone 2. Max of 3 spots >.003" per tube which are limited to Zone 3.

 

Spot Size Zone 1 Zone 2 Zone 3
(Inches) Limit Limit Limit
>.012 0 0 0
>.009 0 0 0
>.006-.009 0 0 1
>.003-.006 0 0 2
Bright Spots 0 0 0
Dark spots </= .003” are acceptable

 

A final note-

As manufacturing capability has improved and technology has continued to advance, many tubes now well exceed their model minimums for FOM, SNR, and Center Resolution. While spots are a normal by-product of the intensifier tube manufacturing process, they are becoming smaller and less frequent.

Model minimums only define the minimum performance threshold that a tube must meet (UM and UA tubes have no defined maximum). As a result, it is possible for a 18UM tube to exceed the performance of a 20UA tube (or 24UA) both for FOM and cosmetics.