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When users buy uncooled infrared thermal imaging thermometer (hereinafter referred to as "instrument"), they often don't know the relevant indicators of the instrument. Here are the user's needs and the relevant indicators of the instrument.
The core indicators of conventional instruments generally include pixel size, array size, focal length, F value, NETD, MRTD. In the process of model selection, users need to convert their needs into the core technical indicators of the instrument itself, which is also a problem that sales engineers and users need to repeatedly confirm.
To make this matter clear, we have to stand on the user's perspective and the professional perspective of the instrument, analyze the three concepts of spatial resolution, temperature resolution and field angle, and restore these three concepts to the professional perspective of the instrument.
The following is the explanation of related terms:
- Spatial resolution: the physical size of the target that needs the minimum resolution, which can be in millimeters (mm) or milliradians (mrad). For example, the size of hair is generally between 0.02mm-0.12mm.
- Temperature resolution: the temperature difference between the interested target and the background, such as 1 ℃.
- Field angle: according to the distance between the instrument and the target and the target area to be detected, the field angle can be converted.
- Array size: at present, the focal plane of the instrument is array, such as 384 × 288，640 × 480, 640 × 512, 1280 × 1024, whose value represents the number of pixel points in both vertical and horizontal directions.
- Pixel size: the size of each pixel. The conventional size is 17 μ m，12 μ m。
- Focal length: it belongs to the core parameter of optical lens and directly affects the action distance.
- F value: the ratio of the effective aperture of the lens to the focal length. The square of this value is inversely proportional to the energy.
- NETD: full English Name: noise equivalent temperature difference, translated as "noise equivalent temperature difference".
- NETD: full English Name: noise equivalent temperature difference, translated as "noise equivalent temperature difference".
The following is a diagram of the correlation between user needs and the core technical indicators of the instrument:
How to select instruments scientifically and quantitatively
- Select the instrument through the spatial resolution: the spatial resolution is only related to the pixel size and focal length, and the ratio of pixel size and focal length is the spatial resolution. According to the "Johnson criterion", the spatial resolution required by users can be divided into three application scenarios, namely detection, recognition and confirmation. Users need to divide the spatial resolution of the instrument by a weight, and then confirm whether it meets the requirements. The weight values of the three cases of "Johnson criterion" are 6, 6 and 12 respectively.
- Select the instrument through temperature resolution: it is related to pixel size, F value and NETD. Before the core component (detector) of the instrument leaves the factory, the pixel size and NETD values are confirmed. At present, the pixel size has two specifications: 17 μ M and 12 μ m. NETD is basically 50mk and 60mk. If you want to increase the temperature resolution, you need to reduce the F value of the optical system, and the square of this value is inversely proportional to the temperature resolution.
- Select the instrument through the field angle: it is related to the pixel size, focal length and area array size. In the case of price sensitivity, you can choose instruments with small array, such as 384 × 288, and then confirm the two indicators of pixel size and focal length. If you are sensitive to performance, you can choose an instrument with a larger array, such as 640 × 480、1280 × 1024, and then confirm other indicators.
Huajingkang model selection scheme
The company has relatively perfect selection tools for users. Users can select instruments in any way, as shown in the table below.
Click download:华景康作用距离计算.xlsx
