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THERMAL IMAGING PRODUCTS
ThermoScreen
Micro
EL
Introduction
Overview
Applications
How
It Works
Example
Defects
 Short
Detection
Model
Board Comparison
EL
Software
System Components
Specifications
R&D
THERMOELECTRIC PRODUCTS
HP20 TE Controller
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 sales@optotherm.com
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 EL Infrared Circuit Board
Inspection System
Shorts Detection
Short circuits
on a PCBA can be very difficult to troubleshoot. While ICT may
indicate that a short circuit exists, often it cannot locate the precise
location of the defect. Technicians and engineers can spend many hours
locating a single shorts, particularly interlayer and low resistance shorts.
The InfraSight EL
320 thermal imaging camera's
high sensitivity, combined with sophisticated noise reduction and infrared image
enhancement software algorithms, provide the ability to detect and locate
shorts that dissipate less than 1 milliwatt of power and that exhibit
temperature rises of only 0.03°C.
The
process of finding shorts involves powering a board for a short period of
time (e.g., 5 to 10 seconds) using the I/O module's relays to automatically
control power to the board during the test. EL detects and locates
localized areas of temperature increase that result from heat dissipated
within the short due to I2R losses. High resistance shorts
(greater than 10 ohms) usually exhibit temperature increases of at least
1°C. Low resistance shorts dissipate smaller amounts of power (heat)
than do high resistance shorts and are somewhat more difficult to detect.
A 0.5 ohm short, for example, may only exhibit a temperature increase of
0.2°C.
EL
short detection is performed using a software process called
image subtraction. When operating in image subtraction mode, a
reference thermal images is captured immediately prior to powering the
board. This reference image is subtracted from each thermal image that
is captured of the board when it is under power. These "subtracted"
images are then displayed on the screen and represent temperature changes
from the moment power was applied to the board. Using this approach,
temperature changes as small as 0.03°C are sufficient to identify a short.
And to prevent damaging sensitive components near the short, board power can
be automatically disconnected using the I/O module's relays when a short
circuit produces a significant temperature rise.
Example
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Low resistance
and power-to-ground shorts are often the only areas that heat up on a
board during a short detection test. The low resistance short
picture below was located by applying 500 milliamps of current for 5
seconds. |
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The precise
location of the short was determined by overlaying a transparent visual
picture of the board on the thermal image. |
Short Detection Settings
Test Averaging
enables you to detect shorts with a resistance under 1 ohm. Because
low resistance shorts do not dissipate much power and heat, a series of
tests are averaged together to increase test sensitivity.
The Auto Stop
feature opens the I/O module relay, cutting off power to the board, as soon
as the temperature on the short increases above a user-defined threshold.
This safety feature can prevent damaging the board, while still locating the
short.
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