What is the relation between TemperatureLinearResolution and SensorGainMode (temperature range) for the FLIR Ax5 series?

The SensorGainMode register is associated with temperature ranges:

HighGainMode = –25 to +135°C

LowGainMode = –40 to +550°C

TemperatureLinearResolution can be either High (0.04 K factor) or Low (0.4 K factor).

Any combination between SensorGainMode and TemperatureLinearResolution is possible:

HighGainMode with High (resolution)

HighGainMode with Low (resolution)

LowGainMode with High (resolution)

LowGainMode with Low (resolution)

However, the signal is 14 bit, which limits some combinations, i.e.:

LowGainModewith High (resolution)

14 bit = 16 384

16 384 × 0.04 = 655.36 K

655.36 K – 273.15 = 382.21°C.

Even though the SensorGainMode is set to LowGainMode (–40 to +550°C), the camera signal will saturate around 382°C.

Now that the interaction between Temperature Linear and Sensor Gain Mode has been explained, let's turn to theSensorGainMode differences:

Each SensorGainMode option is independent: there is no correlation between these modes. As an example, the camera can be extremely accurate using the HighGainMode, but it can measure veryinaccurate values in theLowGainMode.

Every SensorGainMode is created separately and has different RBF values. By coincidence your camera can output the exact same values using both LowGainMode and HighGainMode, but this is not likely to happen.

Usually the HighGainMode will give better performance for scenes with lower temperatures, since the 14-bit signal is divided across the whole range (–25 – 135°C). So the 16 384 bits are distributed across the 160°C range (that is not the exact range, but illustrates what is happening).

The result is a digital resolution close to 0.01 (160 divided by 16 384).

On the other hand the LowGainMode (–40 to +550°C) will have a range of about 590°C, with a digital resolution of about 0.04.

This comparison of digital resolution is not directly related to the signal output of the camera, but serves to illustrate image generation. The signal resolution is limited to the TemperatureLinearResolution (High 0.04 K or Low 0.4 K).

With that being said, the HighGainMode will output an image with smaller temperature differences (better thermal sensitivity) if compared with the LowGainMode.