BUYING THERMAL? This is a must read before you spend your money and information few resellers will want to discuss outside of what is printed on a box or brochure. FYRLYT digs deeper than this and positions its products and advice on core facts and established principles.
With the release of the FTV 384M-15 monocular and our remote mount FTV 640 we have have received many questions about mK (milliKelvin ratings of sensors). It would seem many are basing their purchasing decision based on this specification.
We also note there is a marketing trend with some brands and resellers that is of concern in our opinion re mK ratings. Much like over rated lumen ratings with lights, mK has seemingly become the favoured 'term' to convince consumers about the superiority of one product or brand over another.
There are basic engineering principles that no slick marketing or sales hype can change and if you want to base a decision on truth you need to get the facts.
Cooled versus uncooled sensors
When purchasing a thermal camera or monocular, it's crucial for consumers to be informed about the limitations of uncooled sensors and the potential overrating of their mK (milliKelvin) ratings. While mK ratings are often touted as a measure of thermal sensitivity, they can be misleading, particularly for uncooled sensors.
Uncooled sensors, the most common type in consumer-grade thermal cameras, operate at ambient temperature without the need for cooling. However, this design comes with inherent limitations in sensitivity compared to cooled sensors, which actively utilise cooling mechanisms to achieve superior performance.
The mK rating, often emphasised in marketing materials, represents the smallest temperature difference a thermal camera can detect. A lower mK rating indicates higher sensitivity, meaning the camera can distinguish finer temperature variations. However, it's important to note that mK ratings are often hypothetical and may not reflect real-world performance.
In uncooled sensors, the mK rating is typically measured under ideal conditions, such as controlled laboratory settings. However, in real-world scenarios, factors like ambient temperature, humidity, and object emissivity can significantly impact the actual sensitivity of the camera.
Cooled sensors, on the other hand, offer superior sensitivity and are less susceptible to environmental influences. However, they are SIGNIFICANTLY more expensive due to their complex cooling mechanisms.
For consumers, it's essential to understand that the mK rating of an uncooled sensor may not accurately represent its real-world performance. While a lower mK rating might suggest higher sensitivity, the actual temperature discrimination capabilities can be affected by environmental factors.
Therefore, consumers should exercise caution when relying solely on mK ratings to compare thermal cameras. Instead, they should consider factors like overall image quality, field of view, and intended use cases to make an informed decision.
A deep dive into the theory...
We will guess few salespeople or resellers will either know this or wish to discuss it. If they refute it? We would suggest looking for advice elsewhere.
The NETD of an uncooled sensor is typically higher than that of a cooled sensor, meaning that it requires a larger temperature difference to produce a detectable signal. This is because uncooled sensors are more susceptible to noise from the sensor itself and the environment.
Another relevant formula is the Detectivity, which is a measure of the sensor's ability to detect a small target against a background of noise. The Detectivity of an uncooled sensor is also typically lower than that of a cooled sensor, meaning that it is less likely to detect a small target in a noisy environment.
These formulas can be used to compare the theoretical performance of different sensor types, but it is important to note that real-world performance can be affected by a variety of factors, such as the specific sensor design, the operating environment, and the signal processing algorithms.
Here is an example of how to use the NETD formula to compare the theoretical performance of an uncooled sensor to a cooled sensor:
NETD = 4√fΔf / (GK * τ) where:
f is the bandwidth of the sensor Δf is the noise bandwidth of the sensor G is the gain of the sensor K is Boltzmann's constant τ is the integration time of the sensor
Let's say that we have an uncooled sensor with a bandwidth of 100 MHz, a noise bandwidth of 10 kHz, a gain of 100, and an integration time of 1 ms. Let's also say that we have a cooled sensor with the same specifications.
Plugging these values into the formula, we get:
NETD_uncooled = 4√(100 MHz * 10 kHz) / (100 * 1.38 × 10^-23 J/K * 1 ms) ≈ 0.25 K
NETD_cooled = 4√(100 MHz * 10 kHz) / (100 * 1.38 × 10^-23 J/K * 10 ms) ≈ 0.05 K
As you can see, the NETD of the uncooled sensor is five times higher than the NETD of the cooled sensor. This means that the uncooled sensor requires a temperature difference that is five times larger than the cooled sensor in order to produce a detectable signal.