DCIS, SMART, HART (followup)

reference post: http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=WDI6b.7843%24J6.2057%40pd7tw3no [edited]
3 - The mA signal is passed through a 250 Ohm resistor to produce a 1-5 V signal for the op amps. Thus there is a minimum of 1 watt power consumption. This is sufficient to exceed most sources of interference.
Walter.
sorry walter for this ghost query, but i fail to understand why a 4 to 20 mA current flowing through 250 ohm, would waste 1000mW 'minimum'. if power consumption is I.R and not I*I.R, i need your tution. i figure the power wasted across resistor as 4mW(4*4*millie*millie*250) to 100mW(20*20*millie*millie*250) please correct wrongness in my understanding.
D'jay
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D'jay,
Sorry, I obviously made a mistake. What time of night was that posted?
The minimum power across the range resistor is 4 mA * 1 V = 4 mW. The maximum power in the whole loop is typically 24 VDC * 20 mA = 480 mW.
4 mW is still much greater than the amount of power involved in a thermocouple signal which might be milli volt^2 * meg Ohm.
What is "ghost query"? I'm not familiar with the term./
Walter.

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