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In several datasheets for electronic components, I have seen a ∝ symbol used as a prefix for a time unit, usually seconds, writing as ∝s. As far as I know ∝ is not a valid SI prefix, so what does it mean? What unit is ∝s?

Comparing different datasheets, I assume it should be rather equivalent to micro prefix, but I'm really not sure.

You can see this use for example in the BT136 datasheet describing "Gate controlled turn-on time" and defining unit as ∝s.

JRE
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Pep
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    Shows up perfectly fine here as µs (Safari, macOS), even with the embedded viewer on that site, or by downloading the PDF and opening it in Preview. – jcaron May 25 '23 at 17:30
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    You just have a problem with your PDF reader, and this is not about electronics. – Massimo Ortolano May 25 '23 at 21:37
  • The PDF also shows fine with μs on Firefox/Linux. Sounds like a Microsoft fail (though I doubt it's an issue in up-to-date versions of Windows and browsers). Really, character encodings should be a non-issue nowadays... http://utf8everywhere.org/ – leftaroundabout May 26 '23 at 11:40
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    Irrespective of the root cause, I think it's useful that this has been brought to the community's attention. – Mark Morgan Lloyd May 27 '23 at 06:59

2 Answers2

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In the common ISO 8859-1 encoding, µ is encoded as 0xB5.

In the Windows Symbol typeface, ∝ is encoded as 0xB5.

The Symbol font has been commonly used for Greek letters; µ is the only Greek letter that is available elsewhere. This appears to be a common mistake.

CL.
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    That's a common issue with Ω (Greek capital omega) for Ohm, with so many documents and datasheets showing a W instead - generating confusion, sometimes. Then it's far better IMHO using the lowercase `u`, even though improperly used – LuC May 24 '23 at 10:12
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    I downloaded the datasheet as a PDF (rather than viewing in the Alldatasheet.com viewer) and the symbol renders correctly. (Most likely the font is embedded in the PDF.) – Theodore May 24 '23 at 20:56
  • The issue (∝ shows where µ should) occurs independently of browser and OS: it's specific to using the obsolete PDF viewer (pdfjsview) at https://pdf1.alldatasheet.com/pdfjsview/web/viewer.html (which is used or not depending on browser). The issue occurs neither in the [pure html version](https://html.alldatasheet.com/html-pdf/16751/PHILIPS/BT136/244/1/BT136.html), nor if [the pdf itself](https://pdf1.alldatasheet.com/datasheet-pdf/download/16751/PHILIPS/BT136.html) is viewed, or downloaded and viewed. – fgrieu May 26 '23 at 19:32
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It is most likely an encoding error in the PDF file. It is simply the wrong symbol.

Here's a section of the BT136 datasheet showing the dynamic characteristics:

enter image description here

It shows ∝s for several things, among them \$dV_{com}/dt\$.

Figure 12 also refers to \$dV_{com}/dt\$, but it uses units of microseconds (us.)

enter image description here

Figure 12 uses the common (also incorrect) convention of using a lower case "u" for micro rather than the correct µ symbol. The dynamic characteristics table probably had the correct symbol in whatever program was used to write the datasheet, but it got mangled in the conversion to PDF.

JRE
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