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To my understanding, ambient temperature is the temperature of the surrounding area while the unit being worked on is powered. While operating temperature is the temperature of the unit itself under heat and power.

I have seen many different explanations online, and most seem to contradict themselves. If the operating temperature of a unit has a maximum of 100°C, then does that mean the chip/components inside the unit can only operate at a max of 100°C? So that should be taken into consideration when adjusting the temperature of the oven. If so, is the only difference between ambient temperature and storage temperature that there is power being delivered to the unit?

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Generally the "Operating Temperature" is listed as a MAXIMUM or a range. That means you should not operate the equipment or device outside those bounds or you risk damage or the device not performing according to specs. In my opinion "Ambient" is the same although different manufacturers may have different definitions for this. Here it pays to read their documentation carefully if you are going to be approaching these limits.

"Storage Temp." is also often given as a range and states the limits at which the device or equipment should be stored. Outside that range may cause damage.

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I'm not sure there is a universally accepted definition, especially considering the wide range of possible equipment etc. There are probably military standards that nail it down in that domain.

Without further information, I would interpret "operating temperature" as ambient temperature during operation and storage temperature as ambient temperature during storage (not powered).

If the unit is not powered, typically the internal temperature would be the same as the ambient. When powered, the internal temperature would typically be higher and more variable (some components heat more than others).

There's a lot more nuance possible, because things like lifetime can vary strongly with temperature so storing a device at the maximum storage temperature may greatly shorten its lifetime.

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Operating temperature (range) usually means the range of temperatures over which a unit or component has to 1) work and 2) meet all of it's performance parameters. This can be fairly narrow temperature range, 10 deg C to 25 deg C, or a much wider temperature range.

Integrated circuits, for instance, usually come in 3 temperature ranges - Commercial: 0 ° to 70 °C; Industrial: −40 ° to 85 °C; and Military: −55 ° to 125 °C. A component is guaranteed to meet all the performance numbers specified in the data sheet for the specified temperature range. These are all considered "operating" temperature ranges.

When it comes to systems, the situation is usually a bit different. Even for military systems such as airborn radars, the operating temperature is usually more limited than the full mil temp range for parts. -10 deg C to +65 deg C might be a typical operating temperature range for such a system.

The operating temperature range is usually specified by the specification/requirements document for the system.

In this area, ambient and operating temperatures are usually synonymous, as it doesn't make much sense to differentiate between the two. If I have an assembly that is going to be cooled by air being blown through the chassis, the temperature range of that air (the ambient) is the operating temperature range for that assembly. Similarly, if I have an assembly that is going to be be cooled by conduction and bolted to a heat sink of some sort, the temperature of that heat sink is the ambient temperature for that assembly, and also is the operating temperature range.

Now just because you might have a relatively benign operating temperature range for your assembly does not mean that the temperature range for internal boards and components on boards is the same benign range. In almost all cases, the board/components is going to be operating at a higher temperature than the external environment.

Take the earlier example of an assembly mounted to a heat sink. Say that the maximum temperature of that heat sink is 65 deg C. There might be a 10 deg C temperature rise from that heat sink interface to a place inside the chassis. Then there might be another 10 deg C rise from the chassis to the board, and another 10 deg C rise across the board to some component. So that component, an amplifier lets say, needs to be able to operate up to (65+10+10+10)=95 deg C. So we see that the operating temp range for a part (like our amplifier) is usually much wider than the operating (ambient) temp range for the assembly.

Also, just stumbled upon this old post: Ambient temperature vs operating temperature?

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  • \$\begingroup\$ The post that you linked is a little confusing. The answer states that the "Ambient temperature is the temperature of the air around the chip." While the "Operating temperature is the temperature of the chip (die) itself." So in this case the ambient temperature and the operating temperature are different. \$\endgroup\$ – Jaki Fingler Mar 31 at 19:53
  • \$\begingroup\$ I don't agree with some of the things in that old post. Just linked to it as aa FYI. \$\endgroup\$ – SteveSh Mar 31 at 19:57

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