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.
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 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.