If the GD9000 specification sheet shows CO₂ concentration in both ppm and %VOL, the different-looking numbers can be confusing. They express the same volume ratio using different scales, so they can be converted. Unit conversion is useful for comparing values, but it does not by itself tell you the instrument’s accuracy or suitability for a site.
How to convert between ppm and %VOL
ppm expresses a proportion in parts per million, while %VOL is the percentage of the mixture’s volume occupied by the target gas. One percent is one hundredth; expressed in parts per million, it is 10,000 ppm. So multiply %VOL by 10,000 to get ppm, and divide ppm by 10,000 to get %VOL.
Here are some examples: 0.5%VOL × 10,000 = 5,000 ppm. 2%VOL is 20,000 ppm, while 800 ppm ÷ 10,000 = 0.08%VOL. The values before and after conversion are not different concentrations; they are two expressions of the same ratio. This calculation applies when the gas is the same and the units are ppm and %VOL. Conversion does not change the sample composition; it expresses the same ratio on another scale. A display may round the number of digits when the unit changes, so preserve the original unit and displayed precision when comparing records.
Imagine a real-world comparison: an indoor report lists CO₂ at 900 ppm, while a candidate instrument specification is in %VOL. Then 900 ÷ 10,000 = 0.09%VOL. This calculation is valid only when both values represent CO₂ concentration. ppm for CO and %VOL for CO₂ refer to different gases, so the same calculation cannot be used to compare them as the same concentration.
The GD9000 CO₂ range also illustrates the conversion
The published GD9000 user manual lists a CO₂ measurement range of 0.00–5.00%VOL, with 0–50,000 ppm in parentheses. Converting the upper endpoint gives 5.00 × 10,000 = 50,000 ppm, so the endpoints correspond. When reading specifications, first confirm that the gas name and measured quantity are the same, even if the units look different.
Preserve the original unit when copying a number from a document or display. For example, writing `0.8%VOL (converted: 8,000 ppm)` lets you trace both the original scale and the converted value. If you record only `8,000`, it may be unclear later whether the unit was ppm or something else. Keeping the gas name and unit close to the value helps people compare records.
The same display increment does not mean the same accuracy
Resolution is the smallest increment distinguishable on the display; accuracy describes how close a measurement is to a reference value. Range is the concentration interval the instrument is designed to display. These are different specifications. A display with two decimal places means its scale is divided to that place; it does not guarantee an error smaller than that increment.
Suppose, hypothetically, Model A displays increments of 0.01%VOL and Model B increments of 100 ppm. Using the conversion above, 0.01%VOL equals 100 ppm, so their display increments are equivalent after conversion. That information alone cannot establish which model is more accurate. Check the accuracy specifications and test conditions separately.
Check whether the required concentration interval fits the range
The measurement range is the interval a model is designed to display. The published GD9000 specification measures CO₂ up to 5.00%VOL, but that upper limit does not tell you how well it distinguishes small changes at lower concentrations. For example, if you want to monitor indoor conditions, check not only whether the lower concentration interval of interest is within the display range but also the display increment and accuracy information for that interval. If you need to monitor higher concentrations in a process, first check that expected values will not exceed the upper limit. With the same CO₂ instrument, one application may prioritize reading changes at low concentrations while another needs a range that covers higher concentrations. When requirements differ, “wider range” alone is not enough to choose a product.
%LEL cannot be converted with the same calculation
%LEL is the concentration of a flammable gas expressed relative to that gas’s lower explosive limit. Its reference differs from units that directly express a volume ratio in a mixture, such as ppm or %VOL. Therefore, you cannot multiply or divide %LEL by 10,000 to convert it to ppm or %VOL. Interpreting it requires the gas-specific lower explosive limit and the instrument’s calibration and correction conditions.
If you want to compare the units in GD9000 materials with the CO₂ concentration interval you need, tell AI Safety Korea Co., Ltd. the original values and your use case. You can discuss the conversion separately from the model’s range and accuracy specifications.