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Comp science student and Embedded

That's what the 4mA lower limit is for. 4mA at 8V is over

30mW. That's _tons_ of power. You can run quite a bit of analog circuitry and a pretty decent 8/16-bit processor with that much power. I've worked on microprocessor designs where the availble power was more like 3mW.

Tell that to the millions of measurement devices out there that run on 3.6mA at 9V. Most 4mA devices have analog outputs that actually go down to 3.8-3.9 before the process value limits, and then there's usually a hardware "alarm" state that can be configured to be either low (3.6mA) or high (22-24ma). So the worst case power is usually figured to be at 3.6mA of loop current.

He doesn't. 8-9V is a typical minimum voltage for a 4-20mA device. Not everyting is a Pentium VIII Core Octa running MS Vista Ultimate Premium you know.

[For some high-power devices, there is a separate pair for power, but the vast majority of 4-20 devices are two-wire.] 
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Grant
Reply to
Grant Edwards
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We weren't talking about LEDs. We were talking about sensors (pressure, temperature, flow, etc.).

Some do. Many, many of them don't. A lot of process control products run on few milliwats.

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Grant
Reply to
Grant Edwards

Got it. The part that wasn't obvious to a foriegner was that you were a PO employee and this was training provided to their technical staff.

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Grant
Reply to
Grant Edwards

John Atanasoff of Iowa State University (nee College) and his grad student Clifford Berry built the first automatic electronic computer during the winter of '37-'38. It wasn't a "stored program" computer in that the programming was done with patch cords rather that with instructions stored in addressable memory. They also invented the regenerative capacitor memory cell (basicaly what we call DRAM today).

The ENIAC built in 1943 was held to be derived from the work of Atanosoff.

The Z1, built at the same time as the Atanasoff-Berry computer can probably lay clain to be the first programmable binary computer, but it was an electrically driven mechanical computer rather than an electronic one.

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Reply to
Grant Edwards

Peripherally. Much of the UK work was handed over to bootstrap the US efforts in case the unsinkable aircraft carrier got boarded.

Also the Internet was not solely a US invention the note I have from the

1973 NATO meeting clearly show that some of the significant input came from the UK, Canada and the French. It was just that the US had a network to trial it on. 
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\/\/\/\/\ Chris Hills  Staffs  England     /\/\/\/\/
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Reply to
Chris H

Also Germans. Check Konrad Zuse. Some people are provincial.

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 [mail]: Chuck F (cbfalconer at maineline dot net) 
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            Try the download section.
Reply to
CBFalconer

The 4-20 mA is a specification for the signalling path. Volts are not involved, except to drive the appropriate mA over the connection. Power is a separate matter.

The only concern you have for volts is the ohmic resistance of the path, voltage dropping components (such as diodes), possibly inductance, etc. The sender controls the current, the receiver detects the current. Just apply Ohms law.

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 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: 
            Try the download section.
Reply to
CBFalconer

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